Description
bool 
pcntl_setpriority ( int priority [, int pid])
     pcntl_setpriority() sets the priority of
     pid to priority.  If
     pid is not specified, the pid of the current
     process is used.
    
     priority is generally a value in the range
     -20 to 20. The default priority
     is 0 while a lower numerical value causes more
     favorable scheduling.  Because priority levels can differ between
     system types and kernel versions, please see your system's setpriority(2)
     man page for specific details.
    
     如果成功则返回 TRUE,失败则返回 FALSE。