IPC::Run::Win32Helper
IPC::Run::Win32HelperUser Contributed Perl DocumentatIPC::Run::Win32Helper(3)
NAME
IPC::Run::Win32Helper - helper routines for IPC::Run on Win32 plat-
forms.
SYNOPSIS
use IPC::Run::Win32Helper; # Exports all by default
DESCRIPTION
IPC::Run needs to use sockets to redirect subprocess I/O so that the
select() loop will work on Win32. This seems to only work on WinNT and
Win2K at this time, not sure if it will ever work on Win95 or Win98.
If you have experience in this area, please contact me at bar-
ries@slaysys.com, thanks!.
FUNCTIONS
optimize()
Most common incantations of "run()" (not "harness()", "start()",
or "finish()") now use temporary files to redirect input and out-
put instead of pumper processes.
Temporary files are used when sending to child processes if input
is taken from a scalar with no filter subroutines. This is the
only time we can assume that the parent is not interacting with
the child’s redirected input as it runs.
Temporary files are used when receiving from children when output
is to a scalar or subroutine with or without filters, but only if
the child in question closes its inputs or takes input from unfil-
tered SCALARs or named files. Normally, a child inherits its
STDIN from its parent; to close it, use "0<&-" or the "noinherit
=" 1> option. If data is sent to the child from CODE refs, file-
handles or from scalars through filters than the child’s outputs
will not be optimized because "optimize()" assumes the parent is
interacting with the child. It is ok if the output is filtered or
handled by a subroutine, however.
This assumes that all named files are real files (as opposed to
named pipes) and won’t change; and that a process is not communi-
cating with the child indirectly (through means not visible to
IPC::Run). These can be an invalid assumptions, but are the 99%
case. Write me if you need an option to enable or disable opti-
mizations; I suspect it will work like the "binary()" modifier.
To detect cases that you might want to optimize by closing inputs,
try setting the "IPCRUNDEBUG" environment variable to the special
"notopt" value:
C:> set IPCRUNDEBUG=notopt
C:> my_app_that_uses_IPC_Run.pl
optimizer() rationalizations
Only for that limited case can we be sure that it’s ok to batch
all the input in to a temporary file. If STDIN is from a SCALAR
or from a named file or filehandle (again, only in "run()"), then
outputs to CODE refs are also assumed to be safe enough to batch
through a temp file, otherwise only outputs to SCALAR refs are
batched. This can cause a bit of grief if the parent process ben-
efits from or relies on a bit of "early returns" coming in before
the child program exits. As long as the output is redirected to a
SCALAR ref, this will not be visible. When output is redirected
to a subroutine or (deprecated) filters, the subroutine will not
get any data until after the child process exits, and it is likely
to get bigger chunks of data at once.
The reason for the optimization is that, without it, "pumper" pro-
cesses are used to overcome the inconsistancies of the Win32 API.
We need to use anonymous pipes to connect to the child processes’
stdin, stdout, and stderr, yet select() does not work on these.
select() only works on sockets on Win32. So for each redirected
child handle, there is normally a "pumper" process that connects
to the parent using a socket--so the parent can select() on that
fd--and to the child on an anonymous pipe--so the child can
read/write a pipe.
Using a socket to connect directly to the child (as at least one
MSDN article suggests) seems to cause the trailing output from
most children to be lost. I think this is because child processes
rarely close their stdout and stderr explicitly, and the winsock
dll does not seem to flush output when a process that uses it
exits without explicitly closing them.
Because of these pumpers and the inherent slowness of Win32 Cre-
ateProcess(), child processes with redirects are quite slow to
launch; so this routine looks for the very common case of read-
ing/writing to/from scalar references in a run() routine and con-
verts such reads and writes in to temporary file reads and writes.
Such files are marked as FILE_ATTRIBUTE_TEMPORARY to increase
speed and as FILE_FLAG_DELETE_ON_CLOSE so it will be cleaned up
when the child process exits (for input files). The user’s
default permissions are used for both the temporary files and the
directory that contains them, hope your Win32 permissions are
secure enough for you. Files are created with the Win32API::File
defaults of FILE_SHARE_READ│FILE_SHARE_WRITE.
Setting the debug level to "details" or "gory" will give detailed
information about the optimization process; setting it to "basic"
or higher will tell whether or not a given call is optimized.
Setting it to "notopt" will highligh those calls that aren’t opti-
mized.
win32_parse_cmd_line
@words = win32_parse_cmd_line( q{foo bar ’baz baz’ "bat bat"} ) ;
returns 4 words. This parses like the bourne shell (see the bit
about shellwords() in Text::ParseWords), assuming we’re trying to
be a little cross-platform here. The only difference is that "\"
is *not* treated as an escape except when it precedes punctuation,
since it’s used all over the place in DOS path specs.
TODO: globbing? probably not (it’s unDOSish).
TODO: shebang emulation? Probably, but perhaps that should be part
of Run.pm so all spawned processes get the benefit.
LIMITATIONS: shellwords dies silently on malformed input like
a\"
win32_spawn
Spawns a child process, possibly with STDIN, STDOUT, and STDERR
(file descriptors 0, 1, and 2, respectively) redirected.
LIMITATIONS.
Cannot redirect higher file descriptors due to lack of support for
this in the Win32 environment.
This can be worked around by marking a handle as inheritable in
the parent (or leaving it marked; this is the default in perl),
obtaining it’s Win32 handle with "Win32API::GetOSFHandle(FH)" or
"Win32API::FdGetOsFHandle($fd)" and passing it to the child using
the command line, the environment, or any other IPC mechanism
(it’s a plain old integer). The child can then use "OsFHan-
dleOpen()" or "OsFHandleOpenFd()" and possibly "<open FOO
""&BAR">> or "<open FOO ""&$fd>> as need be. Ach, the pain!
Remember to check the Win32 handle against INVALID_HANDLE_VALUE.
AUTHOR
Barries Slaymaker <barries@slaysys.com>. Funded by Perforce Software,
Inc.
COPYRIGHT
Copyright 2001, Barrie Slaymaker, All Rights Reserved.
You may use this under the terms of either the GPL 2.0 ir the Artistic
License.
perl v5.8.8 2006-05-10 IPC::Run::Win32Helper(3)
