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perlos2




SYNOPSIS

       One can read this document in the following formats:

               man perlos2
               view perl perlos2
               explorer perlos2.html
               info perlos2

       to list some (not all may be available simultaneously), or
       it may be read as is: either as README.os2, or pod/per­
       los2.pod.

       To read the .INF version of documentation (very recom­
       mended) outside of OS/2, one needs an IBM's reader (may be
       available on IBM ftp sites (?)  (URL anyone?)) or shipped
       with PC DOS 7.0 and IBM's Visual Age C++ 3.5.

       A copy of a Win* viewer is contained in the "Just add OS/2
       Warp" package

         ftp://ftp.software.ibm.com/ps/products/os2/tools/jaow/jaow.zip

       in ?:\JUST_ADD\view.exe. This gives one an access to EMX's
       .INF docs as well (text form is available in /emx/doc in
       EMX's distribution).  There is also a different viewer
       named xview.

       Note that if you have lynx.exe or netscape.exe installed,
       you can follow WWW links from this document in .INF for­
       mat. If you have EMX docs installed correctly, you can
       follow library links (you need to have "view emxbook"
       working by setting "EMXBOOK" environment variable as it is
       described in EMX docs).


DESCRIPTION

       Target

       The target is to make OS/2 one of the best supported plat­
       form for using/building/developing Perl and Perl applica­
       tions, as well as make Perl the best language to use under
       OS/2. The secondary target is to try to make this work
       under DOS and Win* as well (but not too hard).

       The current state is quite close to this target. Known
       limitations:

       ·    Some *nix programs use fork() a lot; with the mostly
            useful flavors of perl for OS/2 (there are several
            built simultaneously) this is supported; but some
            flavors do not support this (e.g., when Perl is
            called from inside REXX).  Using fork() after useing
            only way I know is via "OS2::REXX" and "SOM" exten­
            sions (see OS2::REXX, Som).  However, we do not have
            access to convenience methods of Object-REXX. (Is it
            possible at all? I know of no Object-REXX API.)  The
            "SOM" extension (currently in alpha-text) may eventu­
            ally remove this shortcoming; however, due to the
            fact that DII is not supported by the "SOM" module,
            using "SOM" is not as convenient as one would like
            it.

       Please keep this list up-to-date by informing me about
       other items.

       Other OSes

       Since OS/2 port of perl uses a remarkable EMX environment,
       it can run (and build extensions, and - possibly - be
       built itself) under any environment which can run EMX. The
       current list is DOS, DOS-inside-OS/2, Win0.3*, Win0.95 and
       WinNT. Out of many perl flavors, only one works, see
       "perl_.exe".

       Note that not all features of Perl are available under
       these environments. This depends on the features the
       extender - most probably RSX - decided to implement.

       Cf. Prerequisites.

       Prerequisites

       EMX   EMX runtime is required (may be substituted by RSX).
             Note that it is possible to make perl_.exe to run
             under DOS without any external support by binding
             emx.exe/rsx.exe to it, see emxbind. Note that under
             DOS for best results one should use RSX runtime,
             which has much more functions working (like "fork",
             "popen" and so on). In fact RSX is required if there
             is no VCPI present. Note the RSX requires DPMI.
             Many implementations of DPMI are known to be very
             buggy, beware!

             Only the latest runtime is supported, currently
             "0.9d fix 03". Perl may run under earlier versions
             of EMX, but this is not tested.

             One can get different parts of EMX from, say

               http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/
               http://powerusersbbs.com/pub/os2/dev/   [EMX+GCC Development]
               http://hobbes.nmsu.edu/pub/os2/dev/emx/v0.9d/

             work with VCPI only, as EMX would, it requires DMPI.

             Having RSX and the latest sh.exe one gets a fully
             functional *nix-ish environment under DOS, say,
             "fork", `` and pipe-"open" work. In fact, MakeMaker
             works (for static build), so one can have Perl
             development environment under DOS.

             One can get RSX from, say

               ftp://ftp.cdrom.com/pub/os2/emx09c/contrib
               ftp://ftp.uni-bielefeld.de/pub/systems/msdos/misc
               ftp://ftp.leo.org/pub/comp/os/os2/leo/devtools/emx+gcc/contrib

             Contact the author on "rainer@mathematik.uni-biele­
             feld.de".

             The latest sh.exe with DOS hooks is available in

               http://www.ilyaz.org/software/os2/

             as sh_dos.zip or under similar names starting with
             "sh", "pdksh" etc.

       HPFS  Perl does not care about file systems, but the perl
             library contains many files with long names, so to
             install it intact one needs a file system which sup­
             ports long file names.

             Note that if you do not plan to build the perl
             itself, it may be possible to fool EMX to truncate
             file names. This is not supported, read EMX docs to
             see how to do it.

       pdksh To start external programs with complicated command
             lines (like with pipes in between, and/or quoting of
             arguments), Perl uses an external shell. With EMX
             port such shell should be named sh.exe, and located
             either in the wired-in-during-compile locations
             (usually F:/bin), or in configurable location (see
             "PERL_SH_DIR").

             For best results use EMX pdksh. The standard binary
             (5.2.14 or later) runs under DOS (with RSX) as well,
             see

               http://www.ilyaz.org/software/os2/

       Starting Perl programs under OS/2 (and DOS and...)

       Start your Perl program foo.pl with arguments "arg1 arg2
       arg3" the same way as on any other platform, by

               foo arg1 arg2 arg3

       Note that because of stupid OS/2 limitations the full path
       of the perl script is not available when you use
       "extproc", thus you are forced to use "-S" perl switch,
       and your script should be on the "PATH". As a plus side,
       if you know a full path to your script, you may still
       start it with

               perl ../../blah/foo.cmd arg1 arg2 arg3

       (note that the argument "-my_opts" is taken care of by the
       "extproc" line in your script, see ""extproc" on the first
       line").

       To understand what the above magic does, read perl docs
       about "-S" switch - see perlrun, and cmdref about
       "extproc":

               view perl perlrun
               man perlrun
               view cmdref extproc
               help extproc

       or whatever method you prefer.

       There are also endless possibilities to use executable
       extensions of 4os2, associations of WPS and so on... How­
       ever, if you use *nixish shell (like sh.exe supplied in
       the binary distribution), you need to follow the syntax
       specified in "Switches" in perlrun.

       Note that -S switch supports scripts with additional
       extensions .cmd, .btm, .bat, .pl as well.

       Starting OS/2 (and DOS) programs under Perl

       This is what system() (see "system" in perlfunc), `` (see
       "I/O Operators" in perlop), and open pipe (see "open" in
       perlfunc) are for. (Avoid exec() (see "exec" in perlfunc)
       unless you know what you do).

       Note however that to use some of these operators you need
       to have a sh-syntax shell installed (see "Pdksh", "Fre­
       quently asked questions"), and perl should be able to find
       it (see "PERL_SH_DIR").

       The cases when the shell is used are:

       1   One-argument system() (see "system" in perlfunc),
           exec() (see "exec" in perlfunc) with redirection or

       5   If the executable called by sys­
           tem()/exec()/pipe-open()/`` is a script without
           "magic" line, and $ENV{EXECSHELL} is set to shell;

       6   If the executable called by sys­
           tem()/exec()/pipe-open()/`` is not found (is not this
           remark obsolete?);

       7   For globbing (see "glob" in perlfunc, "I/O Operators"
           in perlop) (obsolete? Perl uses builtin globbing nowa­
           days...).

       For the sake of speed for a common case, in the above
       algorithms backslashes in the command name are not consid­
       ered as shell metacharacters.

       Perl starts scripts which begin with cookies "extproc" or
       "#!" directly, without an intervention of shell.  Perl
       uses the same algorithm to find the executable as pdksh:
       if the path on "#!" line does not work, and contains "/",
       then the directory part of the executable is ignored, and
       the executable is searched in . and on "PATH".  To find
       arguments for these scripts Perl uses a different algo­
       rithm than pdksh: up to 3 arguments are recognized, and
       trailing whitespace is stripped.

       If a script does not contain such a cooky, then to avoid
       calling sh.exe, Perl uses the same algorithm as pdksh: if
       $ENV{EXECSHELL} is set, the script is given as the first
       argument to this command, if not set, then "$ENV{COMSPEC}
       /c" is used (or a hardwired guess if $ENV{COMSPEC} is not
       set).

       When starting scripts directly, Perl uses exactly the same
       algorithm as for the search of script given by -S command-
       line option: it will look in the current directory, then
       on components of $ENV{PATH} using the following order of
       appended extensions: no extension, .cmd, .btm, .bat, .pl.

       Note that Perl will start to look for scripts only if OS/2
       cannot start the specified application, thus "system
       'blah'" will not look for a script if there is an exe­
       cutable file blah.exe anywhere on "PATH".  In other words,
       "PATH" is essentially searched twice: once by the OS for
       an executable, then by Perl for scripts.

       Note also that executable files on OS/2 can have an arbi­
       trary extension, but .exe will be automatically appended
       if no dot is present in the name.  The workaround is as
       simple as that:  since blah. and blah denote the same file
       (at list on FAT and HPFS file systems), to start an exe­
       cutable residing in file n:/bin/blah (no extension) give
       Perl binary distributions come with a testperl.cmd script
       which tries to detect common problems with misconfigured
       installations.  There is a pretty large chance it will
       discover which step of the installation you managed to
       goof.  ";-)"

       I cannot run external programs

       ·   Did you run your programs with "-w" switch? See "2
           (and DOS) programs under Perl" in Starting OS.

       ·   Do you try to run internal shell commands, like `copy
           a b` (internal for cmd.exe), or `glob a*b` (internal
           for ksh)? You need to specify your shell explicitly,
           like `cmd /c copy a b`, since Perl cannot deduce which
           commands are internal to your shell.

       I cannot embed perl into my program, or use perl.dll from
       my program.

       Is your program EMX-compiled with "-Zmt -Zcrtdll"?
           Well, nowadays Perl DLL should be usable from a dif­
           ferently compiled program too...  If you can run Perl
           code from REXX scripts (see OS2::REXX), then there are
           some other aspect of interaction which are overlooked
           by the current hackish code to support differently-
           compiled principal programs.

           If everything else fails, you need to build a stand-
           alone DLL for perl. Contact me, I did it once. Sockets
           would not work, as a lot of other stuff.

       Did you use ExtUtils::Embed?
           Some time ago I had reports it does not work.  Nowa­
           days it is checked in the Perl test suite, so grep ./t
           subdirectory of the build tree (as well as *.t files
           in the ./lib subdirectory) to find how it should be
           done "correctly".

       `` and pipe-"open" do not work under DOS.

       This may a variant of just "I cannot run external pro­
       grams", or a deeper problem. Basically: you need RSX (see
       "Prerequisites") for these commands to work, and you may
       need a port of sh.exe which understands command arguments.
       One of such ports is listed in "Prerequisites" under RSX.
       Do not forget to set variable ""PERL_SH_DIR"" as well.

       DPMI is required for RSX.


       Use one of

         system 'cmd', '/c', 'find "pattern" file';
         `cmd /c 'find "pattern" file'`

       This would start find.exe via cmd.exe via "sh.exe" via
       "perl.exe", but this is a price to pay if you want to use
       non-conforming program.


INSTALLATION

       Automatic binary installation

       The most convenient way of installing a binary distribu­
       tion of perl is via perl installer install.exe. Just fol­
       low the instructions, and 99% of the installation blues
       would go away.

       Note however, that you need to have unzip.exe on your
       path, and EMX environment running. The latter means that
       if you just installed EMX, and made all the needed changes
       to Config.sys, you may need to reboot in between. Check
       EMX runtime by running

               emxrev

       Binary installer also creates a folder on your desktop
       with some useful objects.  If you need to change some
       aspects of the work of the binary installer, feel free to
       edit the file Perl.pkg.  This may be useful e.g., if you
       need to run the installer many times and do not want to
       make many interactive changes in the GUI.

       Things not taken care of by automatic binary installation:

       "PERL_BADLANG" may be needed if you change your codepage
                      after perl installation, and the new value
                      is not supported by EMX. See "PERL_BAD­
                      LANG".

       "PERL_BADFREE" see "PERL_BADFREE".

       Config.pm      This file resides somewhere deep in the
                      location you installed your perl library,
                      find it out by

                        perl -MConfig -le "print $INC{'Config.pm'}"

                      While most important values in this file
                      are updated by the binary installer, some
                      of them may need to be hand-edited. I know
                      no such data, please keep me informed if

       Note that the extraction with the stored paths is still
       necessary (default with unzip, specify "-d" to pkunzip).
       However, you need to know where to extract the files. You
       need also to manually change entries in Config.sys to
       reflect where did you put the files. Note that if you have
       some primitive unzipper (like "pkunzip"), you may get a
       lot of warnings/errors during unzipping. Upgrade to
       "(w)unzip".

       Below is the sample of what to do to reproduce the config­
       uration on my machine.  In VIEW.EXE you can press
       "Ctrl-Insert" now, and cut-and-paste from the resulting
       file - created in the directory you started VIEW.EXE from.

       For each component, we mention environment variables
       related to each installation directory.  Either choose
       directories to match your values of the variables, or cre­
       ate/append-to variables to take into account the directo­
       ries.

       Perl VIO and PM executables (dynamically linked)
            unzip perl_exc.zip *.exe *.ico -d f:/emx.add/bin
            unzip perl_exc.zip *.dll -d f:/emx.add/dll

          (have the directories with "*.exe" on PATH, and "*.dll"
          on LIBPATH);

       Perl_ VIO executable (statically linked)
            unzip perl_aou.zip -d f:/emx.add/bin

          (have the directory on PATH);

       Executables for Perl utilities
            unzip perl_utl.zip -d f:/emx.add/bin

          (have the directory on PATH);

       Main Perl library
            unzip perl_mlb.zip -d f:/perllib/lib

          If this directory is exactly the same as the prefix
          which was compiled into perl.exe, you do not need to
          change anything. However, for perl to find the library
          if you use a different path, you need to "set PERL­
          LIB_PREFIX" in Config.sys, see "PERLLIB_PREFIX".

       Additional Perl modules
            unzip perl_ste.zip -d f:/perllib/lib/site_perl/5.8.3/

          Same remark as above applies.  Additionally, if this
          directory is not one of directories on @INC (and @INC
            unzip perl_man.zip -d f:/perllib/man

          This directory should better be on "MANPATH". You need
          to have a working man to access these files.

       Manpages for Perl modules
            unzip perl_mam.zip -d f:/perllib/man

          This directory should better be on "MANPATH". You need
          to have a working man to access these files.

       Source for Perl documentation
            unzip perl_pod.zip -d f:/perllib/lib

          This is used by the "perldoc" program (see perldoc),
          and may be used to generate HTML documentation usable
          by WWW browsers, and documentation in zillions of other
          formats: "info", "LaTeX", "Acrobat", "FrameMaker" and
          so on.  [Use programs such as pod2latex etc.]

       Perl manual in .INF format
            unzip perl_inf.zip -d d:/os2/book

          This directory should better be on "BOOKSHELF".

       Pdksh
            unzip perl_sh.zip -d f:/bin

          This is used by perl to run external commands which
          explicitly require shell, like the commands using redi­
          rection and shell metacharacters. It is also used
          instead of explicit /bin/sh.

          Set "PERL_SH_DIR" (see "PERL_SH_DIR") if you move
          sh.exe from the above location.

          Note. It may be possible to use some other sh-compati­
          ble shell (untested).

       After you installed the components you needed and updated
       the Config.sys correspondingly, you need to hand-edit Con­
       fig.pm. This file resides somewhere deep in the location
       you installed your perl library, find it out by

         perl -MConfig -le "print $INC{'Config.pm'}"

       You need to correct all the entries which look like file
       paths (they currently start with "f:/").

       Warning

       The automatic and manual perl installation leave precom­

         view perl
         view perl perlfunc
         view perl less
         view perl ExtUtils::MakeMaker

       (currently the last two may hit a wrong location, but this
       may improve soon). Under Win* see "SYNOPSIS".

       If you want to build the docs yourself, and have OS/2
       toolkit, run

               pod2ipf > perl.ipf

       in /perllib/lib/pod directory, then

               ipfc /inf perl.ipf

       (Expect a lot of errors during the both steps.) Now move
       it on your BOOKSHELF path.

       Plain text

       If you have perl documentation in the source form, perl
       utilities installed, and GNU groff installed, you may use

               perldoc perlfunc
               perldoc less
               perldoc ExtUtils::MakeMaker

       to access the perl documentation in the text form (note
       that you may get better results using perl manpages).

       Alternately, try running pod2text on .pod files.

       Manpages

       If you have man installed on your system, and you
       installed perl manpages, use something like this:

               man perlfunc
               man 3 less
               man ExtUtils.MakeMaker

       to access documentation for different components of Perl.
       Start with

               man perl

       Note that dot (.) is used as a package separator for docu­
       mentation for packages, and as usual, sometimes you need
       to give the section - 3 above - to avoid shadowing by the
       do like this

               cd f:/perllib/lib/pod
               pod2html

       After this you can direct your browser the file perl.html
       in this directory, and go ahead with reading docs, like
       this:

               explore file:///f:/perllib/lib/pod/perl.html

       Alternatively you may be able to get these docs prebuilt
       from CPAN.

       GNU "info" files

       Users of Emacs would appreciate it very much, especially
       with "CPerl" mode loaded. You need to get latest
       "pod2texi" from "CPAN", or, alternately, the prebuilt info
       pages.

       PDF files

       for "Acrobat" are available on CPAN (may be for slightly
       older version of perl).

       "LaTeX" docs

       can be constructed using "pod2latex".


BUILD

       Here we discuss how to build Perl under OS/2. There is an
       alternative (but maybe older) view on
       <http://www.shadow.net/~troc/os2perl.html>.

       The short story

       Assume that you are a seasoned porter, so are sure that
       all the necessary tools are already present on your sys­
       tem, and you know how to get the Perl source distribution.
       Untar it, change to the extract directory, and

         gnupatch -p0 < os2\diff.configure
         sh Configure -des -D prefix=f:/perllib
         make
         make test
         make install
         make aout_test
         make aout_install

       This puts the executables in f:/perllib/bin.  Manually
       move them to the "PATH", manually move the built perl*.dll
       You need to have the latest EMX development environment,
       the full GNU tool suite (gawk renamed to awk, and GNU
       find.exe earlier on path than the OS/2 find.exe, same with
       sort.exe, to check use

         find --version
         sort --version

       ). You need the latest version of pdksh installed as
       sh.exe.

       Check that you have BSD libraries and headers installed,
       and - optionally - Berkeley DB headers and libraries, and
       crypt.

       Possible locations to get the files:

         ftp://hobbes.nmsu.edu/os2/unix/
         ftp://ftp.cdrom.com/pub/os2/unix/
         ftp://ftp.cdrom.com/pub/os2/dev32/
         ftp://ftp.cdrom.com/pub/os2/emx09c/

       It is reported that the following archives contain enough
       utils to build perl: gnufutil.zip, gnusutil.zip, gnutu­
       til.zip, gnused.zip, gnupatch.zip, gnuawk.zip, gnu­
       make.zip, gnugrep.zip, bsddev.zip and ksh527rt.zip (or a
       later version).  Note that all these utilities are known
       to be available from LEO:

         ftp://ftp.leo.org/pub/comp/os/os2/leo/gnu

       Note also that the db.lib and db.a from the EMX distribu­
       tion are not suitable for multi-threaded compile (even
       single-threaded flavor of Perl uses multi-threaded C RTL,
       for compatibility with XFree86-OS/2). Get a corrected one
       from

         http://www.ilyaz.org/software/os2/db_mt.zip

       If you have exactly the same version of Perl installed
       already, make sure that no copies or perl are currently
       running.  Later steps of the build may fail since an older
       version of perl.dll loaded into memory may be found.

       Also make sure that you have /tmp directory on the current
       drive, and . directory in your "LIBPATH". One may try to
       correct the latter condition by

         set BEGINLIBPATH .\.

       if you use something like CMD.EXE or latest versions of
       4os2.exe.  (Setting BEGINLIBPATH to just "." is ignored by

       Getting perl source

       You need to fetch the latest perl source (including devel­
       opers releases). With some probability it is located in

         http://www.cpan.org/src/5.0
         http://www.cpan.org/src/5.0/unsupported

       If not, you may need to dig in the indices to find it in
       the directory of the current maintainer.

       Quick cycle of developers release may break the OS/2 build
       time to time, looking into

         http://www.cpan.org/ports/os2/

       may indicate the latest release which was publicly
       released by the maintainer. Note that the release may
       include some additional patches to apply to the current
       source of perl.

       Extract it like this

         tar vzxf perl5.00409.tar.gz

       You may see a message about errors while extracting Con­
       figure. This is because there is a conflict with a simi­
       larly-named file configure.

       Change to the directory of extraction.

       Application of the patches

       You need to apply the patches in ./os2/diff.* like this:

         gnupatch -p0 < os2\diff.configure

       You may also need to apply the patches supplied with the
       binary distribution of perl.  It also makes sense to look
       on the perl5-porters mailing list for the latest
       OS/2-related patches (see
       <http://www.xray.mpe.mpg.de/mail­
       ing-lists/perl5-porters/>).  Such patches usually contain
       strings "/os2/" and "patch", so it makes sense looking for
       these strings.

       Hand-editing

       You may look into the file ./hints/os2.sh and correct any­
       thing wrong you find there. I do not expect it is needed
       anywhere.
       Now

         make

       At some moment the built may die, reporting a version mis­
       match or unable to run perl.  This means that you do not
       have . in your LIBPATH, so perl.exe cannot find the needed
       perl67B2.dll (treat these hex digits as line noise).
       After this is fixed the build should finish without a lot
       of fuss.

       Testing

       Now run

         make test

       All tests should succeed (with some of them skipped).  If
       you have the same version of Perl installed, it is crucial
       that you have "." early in your LIBPATH (or in BEGINLIB­
       PATH), otherwise your tests will most probably test the
       wrong version of Perl.

       Some tests may generate extra messages similar to

       A lot of "bad free"
           in database tests related to Berkeley DB. This should
           be fixed already.  If it persists, you may disable
           this warnings, see "PERL_BADFREE".

       Process terminated by SIGTERM/SIGINT
           This is a standard message issued by OS/2 applica­
           tions. *nix applications die in silence. It is consid­
           ered to be a feature. One can easily disable this by
           appropriate sighandlers.

           However the test engine bleeds these message to screen
           in unexpected moments. Two messages of this kind
           should be present during testing.

       To get finer test reports, call

         perl t/harness

       The report with io/pipe.t failing may look like this:

         Failed Test  Status Wstat Total Fail  Failed  List of failed
         ------------------------------------------------------------
         io/pipe.t                    12    1   8.33%  9
         7 tests skipped, plus 56 subtests skipped.
         Failed 1/195 test scripts, 99.49% okay. 1/6542 subtests failed, 99.98% okay.

               4   Checks "atime" and "mtime" of "stat()" -
                   unfortunately, HPFS provides only 2sec time
                   granularity (for compatibility with FAT?).

       Installing the built perl

       If you haven't yet moved "perl*.dll" onto LIBPATH, do it
       now.

       Run

         make install

       It would put the generated files into needed locations.
       Manually put perl.exe, perl__.exe and perl___.exe to a
       location on your PATH, perl.dll to a location on your LIB­
       PATH.

       Run

         make installcmd INSTALLCMDDIR=d:/ir/on/path

       to convert perl utilities to .cmd files and put them on
       PATH. You need to put .EXE-utilities on path manually.
       They are installed in "$prefix/bin", here $prefix is what
       you gave to Configure, see Making.

       If you use "man", either move the installed */man/ direc­
       tories to your "MANPATH", or modify "MANPATH" to match the
       location.  (One could have avoided this by providing a
       correct "manpath" option to ./Configure, or editing ./con­
       fig.sh between configuring and making steps.)

       "a.out"-style build

       Proceed as above, but make perl_.exe (see "perl_.exe") by

         make perl_

       test and install by

         make aout_test
         make aout_install

       Manually put perl_.exe to a location on your PATH.

       Note. The build process for "perl_" does not know about
       all the dependencies, so you should make sure that any­
       thing is up-to-date, say, by doing

         make perl_dll


       Problems with tr or sed

       reported with very old version of tr and sed.

       Some problem (forget which ;-)

       You have an older version of perl.dll on your LIBPATH,
       which broke the build of extensions.

       Library ... not found

       You did not run "omflibs". See Prerequisites.

       Segfault in make

       You use an old version of GNU make. See Prerequisites.

       op/sprintf test failure

       This can result from a bug in emx sprintf which was fixed
       in 0.9d fix 03.


Specific (mis)features of OS/2 port

       "setpriority", "getpriority"

       Note that these functions are compatible with *nix, not
       with the older ports of '94 - 95. The priorities are abso­
       lute, go from 32 to -95, lower is quicker. 0 is the
       default priority.

       WARNING.  Calling "getpriority" on a non-existing process
       could lock the system before Warp3 fixpak22.  Starting
       with Warp3, Perl will use a workaround: it aborts getpri­
       ority() if the process is not present.  This is not possi­
       ble on older versions "2.*", and has a race condition any­
       way.

       "system()"

       Multi-argument form of "system()" allows an additional
       numeric argument. The meaning of this argument is
       described in OS2::Process.

       When finding a program to run, Perl first asks the OS to
       look for executables on "PATH" (OS/2 adds extension .exe
       if no extension is present).  If not found, it looks for a
       script with possible extensions added in this order: no
       extension, .cmd, .btm, .bat, .pl.  If found, Perl checks
       the start of the file for magic strings "#!" and "extproc
       ".  If found, Perl uses the rest of the first line as the
       beginning of the command line to run this script.  The

         system qw(C:/emx.add/bin/bash.exe -x -c C:/emx/bin/foo.cmd bar baz)

       One additional translation is performed: instead of
       /bin/sh Perl uses the hardwired-or-customized shell (see
       ""PERL_SH_DIR"").

       The above search for "interpreter" is recursive: if bash
       executable is not found, but bash.btm is found, Perl will
       investigate its first line etc.  The only hardwired limit
       on the recursion depth is implicit: there is a limit 4 on
       the number of additional arguments inserted before the
       actual arguments given to system().  In particular, if no
       additional arguments are specified on the "magic" first
       lines, then the limit on the depth is 4.

       If Perl finds that the found executable is of PM type when
       the current session is not, it will start the new process
       in a separate session of necessary type.  Call via
       "OS2::Process" to disable this magic.

       WARNING.  Due to the described logic, you need to explic­
       itly specify .com extension if needed.  Moreover, if the
       executable perl5.6.1 is requested, Perl will not look for
       perl5.6.1.exe.  [This may change in the future.]

       "extproc" on the first line

       If the first chars of a Perl script are "extproc ", this
       line is treated as "#!"-line, thus all the switches on
       this line are processed (twice if script was started via
       cmd.exe).  See "DESCRIPTION" in perlrun.

       Additional modules:

       OS2::Process, OS2::DLL, OS2::REXX, OS2::PrfDB,
       OS2::ExtAttr. These modules provide access to additional
       numeric argument for "system" and to the information about
       the running process, to DLLs having functions with REXX
       signature and to the REXX runtime, to OS/2 databases in
       the .INI format, and to Extended Attributes.

       Two additional extensions by Andreas Kaiser, "OS2::UPM",
       and "OS2::FTP", are included into "ILYAZ" directory, mir­
       rored on CPAN.  Other OS/2-related extensions are avail­
       able too.

       Prebuilt methods:

       "File::Copy::syscopy"
           used by "File::Copy::copy", see File::Copy.
           means has drive letter and is_rooted.

       "Cwd::sys_is_rooted(name)"
           means has leading "[/\\]" (maybe after a drive-let­
           ter:).

       "Cwd::sys_is_relative(name)"
           means changes with current dir.

       "Cwd::sys_cwd(name)"
           Interface to cwd from EMX. Used by "Cwd::cwd".

       "Cwd::sys_abspath(name, dir)"
           Really really odious function to implement. Returns
           absolute name of file which would have "name" if CWD
           were "dir".  "Dir" defaults to the current dir.

       "Cwd::extLibpath([type])"
           Get current value of extended library search path. If
           "type" is present and positive, works with "END_LIB­
           PATH", if negative, works with "LIBPATHSTRICT", other­
           wise with "BEGIN_LIBPATH".

       "Cwd::extLibpath_set( path [, type ] )"
           Set current value of extended library search path. If
           "type" is present and positive, works with <END_LIB­
           PATH>, if negative, works with "LIBPATHSTRICT", other­
           wise with "BEGIN_LIBPATH".

       "OS2::Error(do_harderror,do_exception)"
           Returns   "undef" if it was not called yet, otherwise
           bit 1 is set if on the previous call do_harderror was
           enabled, bit 2 is set if on previous call do_exception
           was enabled.

           This function enables/disables error popups associated
           with hardware errors (Disk not ready etc.) and soft­
           ware exceptions.

           I know of no way to find out the state of popups
           before the first call to this function.

       "OS2::Errors2Drive(drive)"
           Returns "undef" if it was not called yet, otherwise
           return false if errors were not requested to be writ­
           ten to a hard drive, or the drive letter if this was
           requested.

           This function may redirect error popups associated
           with hardware errors (Disk not ready etc.) and soft­
           ware exceptions to the file POPUPLOG.OS2 at the root
           directory of the specified drive.  Overrides
                   MAX_PATH_LENGTH, MAX_TEXT_SESSIONS, MAX_PM_SESSIONS,
                   MAX_VDM_SESSIONS, BOOT_DRIVE, DYN_PRI_VARIATION,
                   MAX_WAIT, MIN_SLICE, MAX_SLICE, PAGE_SIZE,
                   VERSION_MAJOR, VERSION_MINOR, VERSION_REVISION,
                   MS_COUNT, TIME_LOW, TIME_HIGH, TOTPHYSMEM, TOTRESMEM,
                   TOTAVAILMEM, MAXPRMEM, MAXSHMEM, TIMER_INTERVAL,
                   MAX_COMP_LENGTH, FOREGROUND_FS_SESSION,
                   FOREGROUND_PROCESS

       OS2::BootDrive()
           Returns a letter without colon.

       "OS2::MorphPM(serve)", "OS2::UnMorphPM(serve)"
           Transforms the current application into a PM applica­
           tion and back.  The argument true means that a real
           message loop is going to be served.  OS2::MorphPM()
           returns the PM message queue handle as an integer.

           See "Centralized management of resources" for addi­
           tional details.

       "OS2::Serve_Messages(force)"
           Fake on-demand retrieval of outstanding PM messages.
           If "force" is false, will not dispatch messages if a
           real message loop is known to be present.  Returns
           number of messages retrieved.

           Dies with "QUITing..." if WM_QUIT message is obtained.

       "OS2::Process_Messages(force [, cnt])"
           Retrieval of PM messages until window cre­
           ation/destruction.  If "force" is false, will not dis­
           patch messages if a real message loop is known to be
           present.

           Returns change in number of windows.  If "cnt" is
           given, it is incremented by the number of messages
           retrieved.

           Dies with "QUITing..." if WM_QUIT message is obtained.

       "OS2::_control87(new,mask)"
           the same as _control87(3) of EMX.  Takes integers as
           arguments, returns the previous coprocessor control
           word as an integer.  Only bits in "new" which are pre­
           sent in "mask" are changed in the control word.

       OS2::get_control87()
           gets the coprocessor control word as an integer.

       "OS2::set_control87_em(new=MCW_EM,mask=MCW_EM)"
           The variant of OS2::_control87() with default values

       Prebuilt variables:

       $OS2::emx_rev
           numeric value is the same as _emx_rev of EMX, a string
           value the same as _emx_vprt (similar to "0.9c").

       $OS2::emx_env
           same as _emx_env of EMX, a number similar to 0x8001.

       $OS2::os_ver
           a number "OS_MAJOR + 0.001 * OS_MINOR".

       $OS2::is_aout
           true if the Perl library was compiled in AOUT format.

       $OS2::can_fork
           true if the current executable is an AOUT EMX exe­
           cutable, so Perl can fork.  Do not use this, use the
           portable check for $Config::Config{dfork}.

       $OS2::nsyserror
           This variable (default is 1) controls whether to
           enforce the contents of $^E to start with
           "SYS0003"-like id.  If set to 0, then the string value
           of $^E is what is available from the OS/2 message
           file.  (Some messages in this file have an
           "SYS0003"-like id prepended, some not.)

       Misfeatures

       ·   Since flock(3) is present in EMX, but is not func­
           tional, it is emulated by perl.  To disable the emula­
           tions, set environment variable "USE_PERL_FLOCK=0".

       ·   Here is the list of things which may be "broken" on
           EMX (from EMX docs):

           ·   The functions recvmsg(3), sendmsg(3), and socket­
               pair(3) are not implemented.

           ·   sock_init(3) is not required and not implemented.

           ·   flock(3) is not yet implemented (dummy function).
               (Perl has a workaround.)

           ·   kill(3):  Special treatment of PID=0, PID=1 and
               PID=-1 is not implemented.

           ·   waitpid(3):
           this already).

           This may lead to problems later in case the socket is
           accessed via the "usual" file-system calls using the
           "initial" name.

       ·   Apparently, IBM used a compiler (for some period of
           time around '95?) which changes FP mask right and
           left.  This is not that bad for IBM's programs, but
           the same compiler was used for DLLs which are used
           with general-purpose applications.  When these DLLs
           are used, the state of floating-point flags in the
           application is not predictable.

           What is much worse, some DLLs change the floating
           point flags when in _DLLInitTerm() (e.g., TCP32IP).
           This means that even if you do not call any function
           in the DLL, just the act of loading this DLL will
           reset your flags.  What is worse, the same compiler
           was used to compile some HOOK DLLs.  Given that HOOK
           dlls are executed in the context of all the applica­
           tions in the system, this means a complete unpre­
           dictablity of floating point flags on systems using
           such HOOK DLLs.  E.g., GAMESRVR.DLL of DIVE origin
           changes the floating point flags on each write to the
           TTY of a VIO (windowed text-mode) applications.

           Some other (not completely debugged) situations when
           FP flags change include some video drivers (?), and
           some operations related to creation of the windows.
           People who code OpenGL may have more experience on
           this.

           Perl is generally used in the situation when all the
           floating-point exceptions are ignored, as is the
           default under EMX.  If they are not ignored, some
           benign Perl programs would get a "SIGFPE" and would
           die a horrible death.

           To circumvent this, Perl uses two hacks.  They help
           against one type of damage only: FP flags changed when
           loading a DLL.

           One of the hacks is to disable floating point excep­
           tions on Perl startup (as is the default with EMX).
           This helps only with compile-time-linked DLLs changing
           the flags before main() had a chance to be called.

           The other hack is to restore FP flags after a call to
           dlopen().  This helps against similar damage done by
           DLLs _DLLInitTerm() at runtime.  Currently no way to
           switch these hacks off is provided.
                created using modified "tmpnam", so there may be
                a race condition.

       "ctermid"
                a dummy implementation.

       "stat"   "os2_stat" special-cases /dev/tty and /dev/con.

       "mkdir", "rmdir"
                these EMX functions do not work if the path con­
                tains a trailing "/".  Perl contains a workaround
                for this.

       "flock"  Since flock(3) is present in EMX, but is not
                functional, it is emulated by perl.  To disable
                the emulations, set environment variable
                "USE_PERL_FLOCK=0".

       Identifying DLLs

       All the DLLs built with the current versions of Perl have
       ID strings identifying the name of the extension, its ver­
       sion, and the version of Perl required for this DLL.  Run
       "bldlevel DLL-name" to find this info.

       Centralized management of resources

       Since to call certain OS/2 API one needs to have a cor­
       rectly initialized "Win" subsystem, OS/2-specific exten­
       sions may require getting "HAB"s and "HMQ"s.  If an exten­
       sion would do it on its own, another extension could fail
       to initialize.

       Perl provides a centralized management of these resources:

       "HAB"
           To get the HAB, the extension should call "hab =
           perl_hab_GET()" in C.  After this call is performed,
           "hab" may be accessed as "Perl_hab".  There is no need
           to release the HAB after it is used.

           If by some reasons perl.h cannot be included, use

             extern int Perl_hab_GET(void);

           instead.

       "HMQ"
           There are two cases:

           *   the extension needs an "HMQ" only because some API
               will not work otherwise.  Use "serve = 0" below.

           NOTE.  If during a shutdown there is a message queue
           which did not disable WM_QUIT, and which did not pro­
           cess the received WM_QUIT message, the shutdown will
           be automatically cancelled.  Do not call
           perl_hmq_GET(1) unless you are going to process mes­
           sages on an orderly basis.

       * Treating errors reported by OS/2 API
           There are two principal conventions (it is useful to
           call them "Dos*" and "Win*" - though this part of the
           function signature is not always determined by the
           name of the API) of reporting the error conditions of
           OS/2 API.  Most of "Dos*" APIs report the error code
           as the result of the call (so 0 means success, and
           there are many types of errors).  Most of "Win*" API
           report success/fail via the result being
           "TRUE"/"FALSE"; to find the reason for the failure one
           should call WinGetLastError() API.

           Some "Win*" entry points also overload a "meaningful"
           return value with the error indicator; having a 0
           return value indicates an error.  Yet some other
           "Win*" entry points overload things even more, and 0
           return value may mean a successful call returning a
           valid value 0, as well as an error condition; in the
           case of a 0 return value one should call WinGetLastEr­
           ror() API to distinguish a successful call from a
           failing one.

           By convention, all the calls to OS/2 API should indi­
           cate their failures by resetting $^E.  All the Perl-
           accessible functions which call OS/2 API may be broken
           into two classes: some die()s when an API error is
           encountered, the other report the error via a false
           return value (of course, this does not concern Perl-
           accessible functions which expect a failure of the
           OS/2 API call, having some workarounds coded).

           Obviously, in the situation of the last type of the
           signature of an OS/2 API, it is must more convenient
           for the users if the failure is indicated by die()ing:
           one does not need to check $^E to know that something
           went wrong.  If, however, this solution is not desir­
           able by some reason, the code in question should reset
           $^E to 0 before making this OS/2 API call, so that the
           caller of this Perl-accessible function has a chance
           to distinguish a success-but-0-return value from a
           failure.  (One may return undef as an alternative way
           of reporting an error.)

           The macros to simplify this type of error propagation
           "SaveCroakWinError(expr,die,name1,name2)"
               Returns "expr", sets $^E from WinGetLastError() if
               "expr" is false, and die()s if "die" and $^E are
               true.  The message to die is the concatenated
               strings "name1" and "name2", separated by ": "
               from the contents of $^E.

           "WinError_2_Perl_rc"
               Sets "Perl_rc" to the return value of WinGet­
               LastError().

           "FillWinError"
               Sets "Perl_rc" to the return value of WinGet­
               LastError(), and sets $^E to the corresponding
               value.

           "FillOSError(rc)"
               Sets "Perl_rc" to "rc", and sets $^E to the corre­
               sponding value.

       * Loading DLLs and ordinals in DLLs
           Some DLLs are only present in some versions of OS/2,
           or in some configurations of OS/2.  Some exported
           entry points are present only in DLLs shipped with
           some versions of OS/2.  If these DLLs and entry points
           were linked directly for a Perl executable/DLL or from
           a Perl extensions, this binary would work only with
           the specified versions/setups.  Even if these entry
           points were not needed, the load of the executable (or
           DLL) would fail.

           For example, many newer useful APIs are not present in
           OS/2 v2; many PM-related APIs require DLLs not avail­
           able on floppy-boot setup.

           To make these calls fail only when the calls are exe­
           cuted, one should call these API via a dynamic linking
           API.  There is a subsystem in Perl to simplify such
           type of calls.  A large number of entry points avail­
           able for such linking is provided (see "entries_ordi­
           nals" - and also "PMWIN_entries" - in os2ish.h).
           These ordinals can be accessed via the APIs:

             CallORD(), DeclFuncByORD(), DeclVoidFuncByORD(),
             DeclOSFuncByORD(), DeclWinFuncByORD(), AssignFuncPByORD(),
             DeclWinFuncByORD_CACHE(), DeclWinFuncByORD_CACHE_survive(),
             DeclWinFuncByORD_CACHE_resetError_survive(),
             DeclWinFunc_CACHE(), DeclWinFunc_CACHE_resetError(),
             DeclWinFunc_CACHE_survive(), DeclWinFunc_CACHE_resetError_survive()

           See the header files and the C code in the supplied
           OS/2-related modules for the details on usage of these

       The main workhorse. This is a chimera executable: it is
       compiled as an "a.out"-style executable, but is linked
       with "omf"-style dynamic library perl.dll, and with
       dynamic CRT DLL. This executable is a VIO application.

       It can load perl dynamic extensions, and it can fork().

       Note. Keep in mind that fork() is needed to open a pipe to
       yourself.

       perl_.exe

       This is a statically linked "a.out"-style executable. It
       cannot load dynamic Perl extensions. The executable sup­
       plied in binary distributions has a lot of extensions pre­
       built, thus the above restriction is important only if you
       use custom-built extensions. This executable is a VIO
       application.

       This is the only executable with does not require OS/2.
       The friends locked into "M$" world would appreciate the
       fact that this executable runs under DOS, Win0.3*, Win0.95
       and WinNT with an appropriate extender. See "Other OSes".

       perl__.exe

       This is the same executable as perl___.exe, but it is a PM
       application.

       Note. Usually (unless explicitly redirected during the
       startup) STDIN, STDERR, and STDOUT of a PM application are
       redirected to nul. However, it is possible to see them if
       you start "perl__.exe" from a PM program which emulates a
       console window, like Shell mode of Emacs or EPM. Thus it
       is possible to use Perl debugger (see perldebug) to debug
       your PM application (but beware of the message loop lock­
       ups - this will not work if you have a message queue to
       serve, unless you hook the serving into the getc() func­
       tion of the debugger).

       Another way to see the output of a PM program is to run it
       as

         pm_prog args 2>&1 | cat -

       with a shell different from cmd.exe, so that it does not
       create a link between a VIO session and the session of
       "pm_porg".  (Such a link closes the VIO window.)  E.g.,
       this works with sh.exe - or with Perl!

         open P, 'pm_prog args 2>&1 |' or die;

       perl___.exe

       This is an "omf"-style executable which is dynamically
       linked to perl.dll and CRT DLL. I know no advantages of
       this executable over "perl.exe", but it cannot fork() at
       all. Well, one advantage is that the build process is not
       so convoluted as with "perl.exe".

       It is a VIO application.

       Why strange names?

       Since Perl processes the "#!"-line (cf.  "DESCRIPTION" in
       perlrun, "Switches" in perlrun, "Not a perl script" in
       perldiag, "No Perl script found in input" in perldiag), it
       should know when a program is a Perl. There is some naming
       convention which allows Perl to distinguish correct lines
       from wrong ones. The above names are almost the only names
       allowed by this convention which do not contain digits
       (which have absolutely different semantics).

       Why dynamic linking?

       Well, having several executables dynamically linked to the
       same huge library has its advantages, but this would not
       substantiate the additional work to make it compile. The
       reason is the complicated-to-developers but very quick and
       convenient-to-users "hard" dynamic linking used by OS/2.

       There are two distinctive features of the dyna-linking
       model of OS/2: first, all the references to external func­
       tions are resolved at the compile time; second, there is
       no runtime fixup of the DLLs after they are loaded into
       memory.  The first feature is an enormous advantage over
       other models: it avoids conflicts when several DLLs used
       by an application export entries with the same name.  In
       such cases "other" models of dyna-linking just choose
       between these two entry points using some random criterion
       - with predictable disasters as results.  But it is the
       second feature which requires the build of perl.dll.

       The address tables of DLLs are patched only once, when
       they are loaded. The addresses of the entry points into
       DLLs are guaranteed to be the same for all the programs
       which use the same DLL.  This removes the runtime fixup -
       once DLL is loaded, its code is read-only.

       While this allows some (significant?) performance advan­
       tages, this makes life much harder for developers, since
       the above scheme makes it impossible for a DLL to be
       "linked" to a symbol in the .EXE file.  Indeed, this would
       (as well as complexity of the compilation). Since inter­
       preter is in a DLL, the C RTL is basically forced to
       reside in a DLL as well (otherwise extensions would not be
       able to use CRT).  There are some advantages if you use
       different flavors of perl, such as running perl.exe and
       perl__.exe simultaneously: they share the memory of
       perl.dll.

       NOTE.  There is one additional effect which makes DLLs
       more wasteful: DLLs are loaded in the shared memory
       region, which is a scarse resource given the 512M barrier
       of the "standard" OS/2 virtual memory.  The code of .EXE
       files is also shared by all the processes which use the
       particular .EXE, but they are "shared in the private
       address space of the process"; this is possible because
       the address at which different sections of the .EXE file
       are loaded is decided at compile-time, thus all the pro­
       cesses have these sections loaded at same addresses, and
       no fixup of internal links inside the .EXE is needed.

       Since DLLs may be loaded at run time, to have the same
       mechanism for DLLs one needs to have the address range of
       any of the loaded DLLs in the system to be available in
       all the processes which did not load a particular DLL yet.
       This is why the DLLs are mapped to the shared memory
       region.

       Why chimera build?

       Current EMX environment does not allow DLLs compiled using
       Unixish "a.out" format to export symbols for data (or at
       least some types of data). This forces "omf"-style compile
       of perl.dll.

       Current EMX environment does not allow .EXE files compiled
       in "omf" format to fork(). fork() is needed for exactly
       three Perl operations:

       ·   explicit fork() in the script,

       ·   "open FH, "|-""

       ·   "open FH, "-|"", in other words, opening pipes to
           itself.

       While these operations are not questions of life and
       death, they are needed for a lot of useful scripts. This
       forces "a.out"-style compile of perl.exe.


ENVIRONMENT

       Here we list environment variables with are either OS/2-
       and DOS- and Win*-specific, or are more important under

       Should be used if the perl library is moved from the
       default location in preference to "PERL(5)LIB", since this
       would not leave wrong entries in @INC.  For example, if
       the compiled version of perl looks for @INC in f:/perl­
       lib/lib, and you want to install the library in
       h:/opt/gnu, do

         set PERLLIB_PREFIX=f:/perllib/lib;h:/opt/gnu

       This will cause Perl with the prebuilt @INC of

         f:/perllib/lib/5.00553/os2
         f:/perllib/lib/5.00553
         f:/perllib/lib/site_perl/5.00553/os2
         f:/perllib/lib/site_perl/5.00553
         .

       to use the following @INC:

         h:/opt/gnu/5.00553/os2
         h:/opt/gnu/5.00553
         h:/opt/gnu/site_perl/5.00553/os2
         h:/opt/gnu/site_perl/5.00553
         .

       "PERL_BADLANG"

       If 0, perl ignores setlocale() failing. May be useful with
       some strange locales.

       "PERL_BADFREE"

       If 0, perl would not warn of in case of unwarranted
       free(). With older perls this might be useful in conjunc­
       tion with the module DB_File, which was buggy when dynami­
       cally linked and OMF-built.

       Should not be set with newer Perls, since this may hide
       some real problems.

       "PERL_SH_DIR"

       Specific for EMX port. Gives the directory part of the
       location for sh.exe.

       "USE_PERL_FLOCK"

       Specific for EMX port. Since flock(3) is present in EMX,
       but is not functional, it is emulated by perl.  To disable
       the emulations, set environment variable
       "USE_PERL_FLOCK=0".
       well-tested EMX layer by some code which should be best
       characterized as a "quick hack".

       In addition to possible bugs and an inability to follow
       changes to the translation policy with off/on switches of
       TERMIO translation, this introduces a serious incompatible
       change: before sysread() on text-mode filehandles would go
       through the translation layer, now it would not.

       Priorities

       "setpriority" and "getpriority" are not compatible with
       earlier ports by Andreas Kaiser. See "setpriority, getpri­
       ority".

       DLL name mangling: pre 5.6.2

       With the release 5.003_01 the dynamically loadable
       libraries should be rebuilt when a different version of
       Perl is compiled. In particular, DLLs (including perl.dll)
       are now created with the names which contain a checksum,
       thus allowing workaround for OS/2 scheme of caching DLLs.

       It may be possible to code a simple workaround which would

       ·   find the old DLLs looking through the old @INC;

       ·   mangle the names according to the scheme of new perl
           and copy the DLLs to these names;

       ·   edit the internal "LX" tables of DLL to reflect the
           change of the name (probably not needed for Perl
           extension DLLs, since the internally coded names are
           not used for "specific" DLLs, they used only for
           "global" DLLs).

       ·   edit the internal "IMPORT" tables and change the name
           of the "old" perl????.dll to the "new" perl????.dll.

       DLL name mangling: 5.6.2 and beyond

       In fact mangling of extension DLLs was done due to misun­
       derstanding of the OS/2 dynaloading model.  OS/2 (effec­
       tively) maintains two different tables of loaded DLL:

       Global DLLs
           those loaded by the base name from "LIBPATH"; includ­
           ing those associated at link time;

       specific DLLs
           loaded by the full name.


       Unless "LIBPATHSTRICT" is set to "T" (and the kernel is
       after 2000/09/01), such DLLs are considered to be global.
       When loading a global DLL it is first looked in the table
       of already-loaded global DLLs.  Because of this the fact
       that one executable loaded a DLL from "BEGINLIBPATH" and
       "ENDLIBPATH", or . from "LIBPATH" may affect which DLL is
       loaded when another executable requests a DLL with the
       same name.  This is the reason for version-specific man­
       gling of the DLL name for perl DLL.

       Since the Perl extension DLLs are always loaded with the
       full path, there is no need to mangle their names in a
       version-specific ways: their directory already reflects
       the corresponding version of perl, and @INC takes into
       account binary compatibility with older version.  Starting
       from 5.6.2 the name mangling scheme is fixed to be the
       same as for Perl 5.005_53 (same as in a popular binary
       release).  Thus new Perls will be able to resolve the
       names of old extension DLLs if @INC allows finding their
       directories.

       However, this still does not guarantee that these DLL may
       be loaded.  The reason is the mangling of the name of the
       Perl DLL.  And since the extension DLLs link with the Perl
       DLL, extension DLLs for older versions would load an older
       Perl DLL, and would most probably segfault (since the data
       in this DLL is not properly initialized).

       There is a partial workaround (which can be made complete
       with newer OS/2 kernels): create a forwarder DLL with the
       same name as the DLL of the older version of Perl, which
       forwards the entry points to the newer Perl's DLL.  Make
       this DLL accessible on (say) the "BEGINLIBPATH" of the new
       Perl executable.  When the new executable accesses old
       Perl's extension DLLs, they would request the old Perl's
       DLL by name, get the forwarder instead, so effectively
       will link with the currently running (new) Perl DLL.

       This may break in two ways:

       ·   Old perl executable is started when a new executable
           is running has loaded an extension compiled for the
           old executable (ouph!).  In this case the old exe­
           cutable will get a forwarder DLL instead of the old
           perl DLL, so would link with the new perl DLL.  While
           not directly fatal, it will behave the same as new
           executable.  This beats the whole purpose of explic­
           itly starting an old executable.

       ·   A new executable loads an extension compiled for the
           old executable when an old perl executable is running.

       them on "SET ..." lines.  From Perl they may be accessed
       by Cwd::extLibpath and Cwd::extLibpath_set.

       DLL forwarder generation

       Assume that the old DLL is named perlE0AC.dll (as is one
       for 5.005_53), and the new version is 5.6.1.  Create a
       file perl5shim.def-leader with

         LIBRARY 'perlE0AC' INITINSTANCE TERMINSTANCE
         DESCRIPTION '@#perl5-porters@perl.org:5.006001#@ Perl module for 5.00553 -> Perl 5.6.1 forwarder'
         CODE LOADONCALL
         DATA LOADONCALL NONSHARED MULTIPLE
         EXPORTS

       modifying the versions/names as needed.  Run

        perl -wnle "next if 0../EXPORTS/; print qq(  \"$1\") if /\"(\w+)\"/" perl5.def >lst

       in the Perl build directory (to make the DLL smaller
       replace perl5.def with the definition file for the older
       version of Perl if present).

        cat perl5shim.def-leader lst >perl5shim.def
        gcc -Zomf -Zdll -o perlE0AC.dll perl5shim.def -s -llibperl

       (ignore multiple "warning L4085").

       Threading

       As of release 5.003_01 perl is linked to multithreaded C
       RTL DLL.  If perl itself is not compiled multi­
       thread-enabled, so will not be perl's malloc(). However,
       extensions may use multiple thread on their own risk.

       This was needed to compile "Perl/Tk" for XFree86-OS/2
       out-of-the-box, and link with DLLs for other useful
       libraries, which typically are compiled with "-Zmt -Zcrt­
       dll".

       Calls to external programs

       Due to a popular demand the perl external program calling
       has been changed wrt Andreas Kaiser's port.  If perl needs
       to call an external program via shell, the f:/bin/sh.exe
       will be called, or whatever is the override, see
       "PERL_SH_DIR".

       Thus means that you need to get some copy of a sh.exe as
       well (I use one from pdksh). The path F:/bin above is set
       up automatically during the build to a correct value on
       the builder machine, but is overridable at runtime,
       (to pretend that the "pid" did not change). This means
       that 1 extra copy of sh.exe is made active via
       fork()/exec(), which may lead to some resources taken from
       the system (even if we do not count extra work needed for
       fork()ing).

       Note that this a lesser issue now when we do not spawn
       sh.exe unless needed (metachars found).

       One can always start cmd.exe explicitly via

         system 'cmd', '/c', 'mycmd', 'arg1', 'arg2', ...

       If you need to use cmd.exe, and do not want to hand-edit
       thousands of your scripts, the long-term solution proposed
       on p5-p is to have a directive

         use OS2::Cmd;

       which will override system(), exec(), ``, and
       "open(,'...|')". With current perl you may override only
       system(), readpipe() - the explicit version of ``, and
       maybe exec(). The code will substitute the one-argument
       call to system() by "CORE::system('cmd.exe', '/c',
       shift)".

       If you have some working code for "OS2::Cmd", please send
       it to me, I will include it into distribution. I have no
       need for such a module, so cannot test it.

       For the details of the current situation with calling
       external programs, see "2 (and DOS) programs under Perl"
       in Starting OS.  Set us mention a couple of features:

       ·   External scripts may be called by their basename.
           Perl will try the same extensions as when processing
           -S command-line switch.

       ·   External scripts starting with "#!" or "extproc " will
           be executed directly, without calling the shell, by
           calling the program specified on the rest of the first
           line.

       Memory allocation

       Perl uses its own malloc() under OS/2 - interpreters are
       usually malloc-bound for speed, but perl is not, since its
       malloc is lightning-fast.  Perl-memory-usage-tuned bench­
       marks show that Perl's malloc is 5 times quicker than EMX
       one.  I do not have convincing data about memory foot­
       print, but a (pretty random) benchmark showed that Perl's
       one is 5% better.
       support of threads is very preliminary.

       Most notable problems:

       "COND_WAIT"
           may have a race condition (but probably does not due
           to edge-triggered nature of OS/2 Event semaphores).
           (Needs a reimplementation (in terms of chaining wait­
           ing threads, with the linked list stored in per-thread
           structure?)?)

       os2.c
           has a couple of static variables used in OS/2-specific
           functions.  (Need to be moved to per-thread structure,
           or serialized?)

       Note that these problems should not discourage experiment­
       ing, since they have a low probability of affecting small
       programs.


BUGS

       This description was not updated since 5.6.1, see
       os2/Changes for more info.


AUTHOR

       Ilya Zakharevich, cpan@ilyaz.org


SEE ALSO

       perl(1).

perl v5.8.1                 2003-09-02                 PERLOS2(1)
  
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