diff options
Diffstat (limited to 'contrib/perl5/pod/perlipc.pod')
| -rw-r--r-- | contrib/perl5/pod/perlipc.pod | 91 |
1 files changed, 62 insertions, 29 deletions
diff --git a/contrib/perl5/pod/perlipc.pod b/contrib/perl5/pod/perlipc.pod index 2f99d10..8760257 100644 --- a/contrib/perl5/pod/perlipc.pod +++ b/contrib/perl5/pod/perlipc.pod @@ -58,7 +58,7 @@ You may also choose to assign the strings C<'IGNORE'> or C<'DEFAULT'> as the handler, in which case Perl will try to discard the signal or do the default thing. -On most UNIX platforms, the C<CHLD> (sometimes also known as C<CLD>) signal +On most Unix platforms, the C<CHLD> (sometimes also known as C<CLD>) signal has special behavior with respect to a value of C<'IGNORE'>. Setting C<$SIG{CHLD}> to C<'IGNORE'> on such a platform has the effect of not creating zombie processes when the parent process fails to C<wait()> @@ -126,7 +126,7 @@ or even the more elaborate: use POSIX ":sys_wait_h"; sub REAPER { my $child; - while ($child = waitpid(-1,WNOHANG)) { + while (($child = waitpid(-1,WNOHANG)) > 0) { $Kid_Status{$child} = $?; } $SIG{CHLD} = \&REAPER; # still loathe sysV @@ -152,6 +152,10 @@ Here's an example: }; if ($@ and $@ !~ /alarm clock restart/) { die } +If the operation being timed out is system() or qx(), this technique +is liable to generate zombies. If this matters to you, you'll +need to do your own fork() and exec(), and kill the errant child process. + For more complex signal handling, you might see the standard POSIX module. Lamentably, this is almost entirely undocumented, but the F<t/lib/posix.t> file from the Perl source distribution has some @@ -276,7 +280,7 @@ same effect as opening a pipe for reading: While this is true on the surface, it's much more efficient to process the file one line or record at a time because then you don't have to read the -whole thing into memory at once. It also gives you finer control of the +whole thing into memory at once. It also gives you finer control of the whole process, letting you to kill off the child process early if you'd like. @@ -307,8 +311,7 @@ To catch it, you could use this: Both the main process and any child processes it forks share the same STDIN, STDOUT, and STDERR filehandles. If both processes try to access -them at once, strange things can happen. You'll certainly want to any -stdio flush output buffers before forking. You may also want to close +them at once, strange things can happen. You may also want to close or reopen the filehandles for the child. You can get around this by opening your pipe with open(), but on some systems this means that the child process cannot outlive the parent. @@ -450,8 +453,8 @@ doesn't actually work: open(PROG_FOR_READING_AND_WRITING, "| some program |") -and if you forget to use the B<-w> flag, then you'll miss out -entirely on the diagnostic message: +and if you forget to use the C<use warnings> pragma or the B<-w> flag, +then you'll miss out entirely on the diagnostic message: Can't do bidirectional pipe at -e line 1. @@ -473,7 +476,6 @@ Here's an example of using open2(): use FileHandle; use IPC::Open2; $pid = open2(*Reader, *Writer, "cat -u -n" ); - Writer->autoflush(); # default here, actually print Writer "stuff\n"; $got = <Reader>; @@ -1022,7 +1024,7 @@ something to the server before fetching the server's response. The web server handing the "http" service, which is assumed to be at its standard port, number 80. If your the web server you're trying to connect to is at a different port (like 1080 or 8080), you should specify -as the named-parameter pair, C<PeerPort =E<gt> 8080>. The C<autoflush> +as the named-parameter pair, C<< PeerPort => 8080 >>. The C<autoflush> method is used on the socket because otherwise the system would buffer up the output we sent it. (If you're on a Mac, you'll also need to change every C<"\n"> in your code that sends data over the network to @@ -1140,7 +1142,7 @@ well. As always, setting up a server is little bit more involved than running a client. The model is that the server creates a special kind of socket that does nothing but listen on a particular port for incoming connections. -It does this by calling the C<IO::Socket::INET-E<gt>new()> method with +It does this by calling the C<< IO::Socket::INET->new() >> method with slightly different arguments than the client did. =over @@ -1159,7 +1161,7 @@ server. (Under Unix, ports under 1024 are restricted to the superuser.) In our sample, we'll use port 9000, but you can use any port that's not currently in use on your system. If you try to use one already in used, you'll get an "Address already in use" -message. Under Unix, the C<netstat -a> command will show +message. Under Unix, the C<netstat -a> command will show which services current have servers. =item Listen @@ -1303,16 +1305,16 @@ you weren't wanting it to. Here's a small example showing shared memory usage. - use IPC::SysV qw(IPC_PRIVATE IPC_RMID S_IRWXU S_IRWXG S_IRWXO); + use IPC::SysV qw(IPC_PRIVATE IPC_RMID S_IRWXU); $size = 2000; - $key = shmget(IPC_PRIVATE, $size, S_IRWXU|S_IRWXG|S_IRWXO) || die "$!"; - print "shm key $key\n"; + $id = shmget(IPC_PRIVATE, $size, S_IRWXU) || die "$!"; + print "shm key $id\n"; $message = "Message #1"; - shmwrite($key, $message, 0, 60) || die "$!"; + shmwrite($id, $message, 0, 60) || die "$!"; print "wrote: '$message'\n"; - shmread($key, $buff, 0, 60) || die "$!"; + shmread($id, $buff, 0, 60) || die "$!"; print "read : '$buff'\n"; # the buffer of shmread is zero-character end-padded. @@ -1320,16 +1322,16 @@ Here's a small example showing shared memory usage. print "un" unless $buff eq $message; print "swell\n"; - print "deleting shm $key\n"; - shmctl($key, IPC_RMID, 0) || die "$!"; + print "deleting shm $id\n"; + shmctl($id, IPC_RMID, 0) || die "$!"; Here's an example of a semaphore: use IPC::SysV qw(IPC_CREAT); $IPC_KEY = 1234; - $key = semget($IPC_KEY, 10, 0666 | IPC_CREAT ) || die "$!"; - print "shm key $key\n"; + $id = semget($IPC_KEY, 10, 0666 | IPC_CREAT ) || die "$!"; + print "shm key $id\n"; Put this code in a separate file to be run in more than one process. Call the file F<take>: @@ -1337,8 +1339,8 @@ Call the file F<take>: # create a semaphore $IPC_KEY = 1234; - $key = semget($IPC_KEY, 0 , 0 ); - die if !defined($key); + $id = semget($IPC_KEY, 0 , 0 ); + die if !defined($id); $semnum = 0; $semflag = 0; @@ -1346,14 +1348,14 @@ Call the file F<take>: # 'take' semaphore # wait for semaphore to be zero $semop = 0; - $opstring1 = pack("sss", $semnum, $semop, $semflag); + $opstring1 = pack("s!s!s!", $semnum, $semop, $semflag); # Increment the semaphore count $semop = 1; - $opstring2 = pack("sss", $semnum, $semop, $semflag); + $opstring2 = pack("s!s!s!", $semnum, $semop, $semflag); $opstring = $opstring1 . $opstring2; - semop($key,$opstring) || die "$!"; + semop($id,$opstring) || die "$!"; Put this code in a separate file to be run in more than one process. Call this file F<give>: @@ -1363,22 +1365,53 @@ Call this file F<give>: # that the second process continues $IPC_KEY = 1234; - $key = semget($IPC_KEY, 0, 0); - die if !defined($key); + $id = semget($IPC_KEY, 0, 0); + die if !defined($id); $semnum = 0; $semflag = 0; # Decrement the semaphore count $semop = -1; - $opstring = pack("sss", $semnum, $semop, $semflag); + $opstring = pack("s!s!s!", $semnum, $semop, $semflag); - semop($key,$opstring) || die "$!"; + semop($id,$opstring) || die "$!"; The SysV IPC code above was written long ago, and it's definitely clunky looking. For a more modern look, see the IPC::SysV module which is included with Perl starting from Perl 5.005. +A small example demonstrating SysV message queues: + + use IPC::SysV qw(IPC_PRIVATE IPC_RMID IPC_CREAT S_IRWXU); + + my $id = msgget(IPC_PRIVATE, IPC_CREAT | S_IRWXU); + + my $sent = "message"; + my $type = 1234; + my $rcvd; + my $type_rcvd; + + if (defined $id) { + if (msgsnd($id, pack("l! a*", $type_sent, $sent), 0)) { + if (msgrcv($id, $rcvd, 60, 0, 0)) { + ($type_rcvd, $rcvd) = unpack("l! a*", $rcvd); + if ($rcvd eq $sent) { + print "okay\n"; + } else { + print "not okay\n"; + } + } else { + die "# msgrcv failed\n"; + } + } else { + die "# msgsnd failed\n"; + } + msgctl($id, IPC_RMID, 0) || die "# msgctl failed: $!\n"; + } else { + die "# msgget failed\n"; + } + =head1 NOTES Most of these routines quietly but politely return C<undef> when they |
