(PHP 5)
pcntl_getpriority — 获取任意进程的优先级
$pid = getmypid()
[, int $process_identifier = PRIO_PROCESS
]] )
pcntl_getpriority() 获取进程号为
pid的进程的优先级。由于不同的系统类型以及内核版本下
优先级可能不同，因此请参考您系统的getpriority（2）手册以获取详细的规范。
pid
如果没有指定，默认是当前进程的进程号。
process_identifier
PRIO_PGRP（译注：获取进程组优先级）, PRIO_USER
（译注：获取用户进程优先级）或 PRIO_PROCESS（译注：默认值;获取进程优先级）三者之一。
pcntl_getpriority() 返回进程的优先级或在错误时返回 FALSE 。 值越小代表优先级越高。
jonathan at jcdesigns dot com (2008-05-15 02:12:47)
This function is ideal for checking if a given process is running, I have seen solutions that involve running the system utilites like PS and parsing the answer, which should work fine, but this allows you to check a given PID with a single call
function CheckPID( $PID )
{
// Check if the passed in PID represents a vlaid process in the system
// Returns true if it does
// Turn off non-fatal runtime warning for a moment as we know we
// will get one if the PID does not represent a valid process
$oldErrorLevel = error_reporting(0);
error_reporting( $oldErrorLevel & ~E_WARNING );
$res = pcntl_getpriority($PID);
error_reporting( $oldErrorLevel);
return ! ( $res === false);
}