=head1 NAME
-perlfork - Perl's fork() emulation (EXPERIMENTAL, subject to change)
+perlfork - Perl's fork() emulation
=head1 SYNOPSIS
- WARNING: As of the 5.6.1 release, the fork() emulation continues
- to be an experimental feature. Use in production applications is
- not recommended. See the "BUGS" and "CAVEATS AND LIMITATIONS"
- sections below.
+ NOTE: As of the 5.8.0 release, fork() emulation has considerably
+ matured. However, there are still a few known bugs and differences
+ from real fork() that might affect you. See the "BUGS" and
+ "CAVEATS AND LIMITATIONS" sections below.
Perl provides a fork() keyword that corresponds to the Unix system call
of the same name. On most Unix-like platforms where the fork() system
waiting pseudo-process that called exec(), not the real process it is
waiting for after the exec().
+When exec() is called inside a pseudo-process then DESTROY methods and
+END blocks will still be called after the external process returns.
+
=item exit()
exit() always exits just the executing pseudo-process, after automatically
wait()-ing for any outstanding child pseudo-processes. Note that this means
that the process as a whole will not exit unless all running pseudo-processes
-have exited.
+have exited. See below for some limitations with open filehandles.
=item Open handles to files, directories and network sockets
One can avoid this by opening files that need distinct seek pointers
separately in the child.
+On some operating systems, notably Solaris and Unixware, calling C<exit()>
+from a child process will flush and close open filehandles in the parent,
+thereby corrupting the filehandles. On these systems, calling C<_exit()>
+is suggested instead. C<_exit()> is available in Perl through the
+C<POSIX> module. Please consult your systems manpages for more information
+on this.
+
=item Forking pipe open() not yet implemented
The C<open(FOO, "|-")> and C<open(BAR, "-|")> constructs are not yet
else {
# child
while (<STDIN>) { print; }
- close STDIN;
exit(0);
}
else {
# child
print "pipe_from_fork\n";
- close STDOUT;
exit(0);
}
=item *
-Perl's regular expression engine currently does not play very nicely
-with the fork() emulation. There are known race conditions arising
-from the regular expression engine modifying state carried in the opcode
-tree at run time (the fork() emulation relies on the opcode tree being
-immutable). This typically happens when the regex contains paren groups
-or variables interpolated within it that force a run time recompilation
-of the regex. Due to this major bug, the fork() emulation is not
-recommended for use in production applications at this time.
-
-=item *
-
Having pseudo-process IDs be negative integers breaks down for the integer
C<-1> because the wait() and waitpid() functions treat this number as
being special. The tacit assumption in the current implementation is that
=item *
+In certain cases, the OS-level handles created by the pipe(), socket(),
+and accept() operators are apparently not duplicated accurately in
+pseudo-processes. This only happens in some situations, but where it
+does happen, it may result in deadlocks between the read and write ends
+of pipe handles, or inability to send or receive data across socket
+handles.
+
+=item *
+
This document may be incomplete in some respects.
=back
https://perl5.git.perl.org / perl5.git / blobdiff