在PHP中，睡眠和睡眠行为在内部表现不同吗？

Question

I have a socket server listening to a connection for incoming data and writing outgoing data during pauses in input. Since this is in a loop I am making a sleep call in order to allow other processes to have some CPU time while my process is not expecting input right away.

I know sleep does this, but does usleep also return execution to the OS? I am suspicious because I know that, traditionally, the sleep syscall only accepts seconds, and a VERY old book I have read about C programming ten years ago said that to "sleep" for shorter intervals involves hacks like making an infinite loop to essentially simulate the sleep call but not cede CPU time to other processes. (This book may have been wrong, or may no longer be accurate, I'm just telling you what it said.)

I am using Linux, PHP versions 5.6 and 7.1

thank you

Answer 1

It is platform-dependent, but on Linux you can use this simple script to test:

$start = microtime(true);

while(true){
        while(microtime(true) - $start < .9){}
}

//while(true){
//      usleep(900000);
//}

Run it with php test.php & top -d 0.1 the first time to observe what a false sleep looks like, kill the spawned php process after done inspecting top , comment out the first while loop and uncomment the second one, re-run the script and note the CPU usage.

Thanks to Halcyon for giving me the idea to test it myself.