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PHP : Function Reference : POSIX Functions : posix_mkfifo

posix_mkfifo

Create a fifo special file (a named pipe) (PHP 4, PHP 5)
bool posix_mkfifo ( string pathname, int mode )


Code Examples / Notes » posix_mkfifo

tech

This is still not a solution: if I listen to commands on a pipe and output status on a separate pipe, PHP will block on both opens because something else has not already connected to this pipe.  Because I can't do a low-level fcntl() to to set O_NONBLOCK or something like it, this always locks up and is really stupid.  The only way I can get it to work is to spawn seperate subshells with system() and have them cat, or echo respectively and then the pipes work properly...usually?  Its alot of trouble that we can't set the blocking on the open!!

uther pendragon

Note (quoted from `man 7 pipe` on debian linux):
"On some systems (but not Linux), pipes are bidirectional:  data  can  be  transmitted  in  both directions  between  the pipe ends.  According to POSIX.1-2001, pipes only need to be unidirectional.  Portable applications should avoid reliance on bidirectional pipe semantics."
Linux pipes are NOT bidirectional.
Also, it appears to me that the use of fifo (named) pipes in php is pretty pointless as there appears to be NO way of determining whether opening (let alone reading) from it will block.  stream_select SHOULD be able to accomplish this, unfortunatly you cannot get to this point because even trying to OPEN a pipe for read will block until there is a writer.
I even tried to use popen("cat $name_of_pipe", 'r'), and even it blocked until it was opened for write by another process.


enric jaen

A way to have a non-blocking pipe reader is to check first if the pipe exists. If so, then read from the pipe, otherwise do other stuff. This will work assuming that the writer creates the pipe, writes on it, and after that deletes the pipe.
This is a blocking writer:
<?php
  $pipe="/tmp/pipe";
  $mode=0600;
  if(!file_exists($pipe)) {
     // create the pipe
     umask(0);
     posix_mkfifo($pipe,$mode);
  }
  $f = fopen($pipe,"w");
  fwrite($f,"hello");  //block until there is a reader
  unlink($pipe); //delete pipe
?>
And this is the non-blocking reader:
<?php
  $pipe="/tmp/pipe";
  if(!file_exists($pipe)) {
     echo "I am not blocked!";
  }
  else {
     //block and read from the pipe
     $f = fopen($pipe,"r");
     echo fread($f,10);
  }
?>


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posix_access
posix_ctermid
posix_get_last_error
posix_getcwd
posix_getegid
posix_geteuid
posix_getgid
posix_getgrgid
posix_getgrnam
posix_getgroups
posix_getlogin
posix_getpgid
posix_getpgrp
posix_getpid
posix_getppid
posix_getpwnam
posix_getpwuid
posix_getrlimit
posix_getsid
posix_getuid
posix_initgroups
posix_isatty
posix_kill
posix_mkfifo
posix_mknod
posix_setegid
posix_seteuid
posix_setgid
posix_setpgid
posix_setsid
posix_setuid
posix_strerror
posix_times
posix_ttyname
posix_uname
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