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(PHP 4 >= 4.1.0, PHP 5, PHP 7, PHP 8)
pcntl_waitpid — Waits on or returns the status of a forked child
$process_id,&$status,$flags = 0,&$resource_usage = []
Suspends execution of the current process until a child as specified by
the process_id argument has exited, or until a signal is
delivered whose action is to terminate the current process or to call a
signal handling function.
If a child as requested by process_id has already exited
by the time of the call (a so-called "zombie" process), the function
returns immediately. Any system resources used by the child are freed.
Please see your system's waitpid(2) man page for specific details as to
how waitpid works on your system.
process_id
The value of process_id can be one of the following:
< -1 |
wait for any child process whose process group ID is equal to
the absolute value of process_id.
|
-1 |
wait for any child process; this is the same behaviour that the pcntl_wait() function exhibits. |
0 |
wait for any child process whose process group ID is equal to that of the calling process. |
> 0 |
wait for the child whose process ID is equal to the value of
process_id.
|
Note:
Specifying
-1as theprocess_idis equivalent to the functionality pcntl_wait() provides (minusflags).
status
pcntl_waitpid() will store status information
in the status parameter which can be
evaluated using the following functions:
pcntl_wifexited(),
pcntl_wifstopped(),
pcntl_wifsignaled(),
pcntl_wexitstatus(),
pcntl_wtermsig() and
pcntl_wstopsig().
flags
The value of flags is the value of zero
or more of the following two global constants
OR'ed together:
WNOHANG |
return immediately if no child has exited. |
WUNTRACED |
return for children which are stopped, and whose status has not been reported. |
resource_usage
The resource_usage parameter is set to an
associative array containing resource usage statistics
from the child process. For information on the contents see
getrusage().
This is only supported if the wait4(2) system call is
available on the system; otherwise the parameter is left untouched.
If no child process was reaped, that is if the function returns
0 or -1, the parameter is set to
an empty array.
pcntl_waitpid() returns the process ID of the
child which exited, -1 on error or zero if WNOHANG was used and no
child was available
Example #1 pcntl_waitpid() example
<?php
function checkChild(int $pid, bool $wait): void
{
$flags = ($wait ? 0 : WNOHANG);
$deadPid = pcntl_waitpid($pid, $status, $flags, $rusage);
if ($deadPid === -1) {
$errNo = pcntl_get_last_error();
$errMsg = pcntl_strerror($errNo);
print "PARENT pcntl_waitpid FAILED ({$errNo}): {$errMsg}\n";
} elseif ($deadPid === 0) {
print "PARENT pcntl_waitpid: No exited children.\n";
} elseif (pcntl_wifexited($status)) {
print "PARENT pcntl_waitpid: Child PID {$deadPid} exited with status: "
. pcntl_wexitstatus($status) . "\n";
var_dump($rusage);
} else {
print "PARENT pcntl_waitpid: Child PID {$deadPid} was terminated by signal: "
. pcntl_wtermsig($status) . "\n";
}
}
$parentPid = getmypid();
$forkedPid = pcntl_fork();
if ($forkedPid == -1) {
die('Could not fork');
} else if ($forkedPid) {
// Parent process
print "PARENT {$parentPid} has forked {$forkedPid}\n";
print "PARENT is checking for exited children\n";
checkChild($forkedPid, false);
// Prevents children remaining as a "zombie process"
print "PARENT is waiting for a child to exit\n";
checkChild($forkedPid, true);
print "PARENT is checking for exited children\n";
checkChild($forkedPid, false);
print "PARENT is exiting\n";
} else {
// Child process
$pid = getmypid();
print "CHILD {$pid} is sleeping\n";
sleep(10);
print "CHILD is exiting\n";
exit(7);
}
