进程互斥问题？

Question

<?php
ini_set('display_errors',1);

ini_set('display_startup_errors',1);

error_reporting(-1);

$file = "/www/tp/signal.txt";
$key  = ftok($file, "x");
$semaphore = sem_get($file, 1, 0666, false);
sem_acquire($semaphore);
echo "hello world";
sleep(20);

我写了一个简单的互斥信号量程序，在两个终端中打开，在没有主动释放信号量的同时，当一个进程结束为什么另一个进程没有被阻塞而是拿到了信号量？进程结束会主动释放信号量吗(程序里没有释放信号量的操作)？希望有大佬帮忙解答一下，为什么两个进程都正常运行了，谢谢！

Answer 1

sem_acquire

sem_acquire() by default blocks (if necessary) until the semaphore can be acquired. A process attempting to acquire a semaphore which it has already acquired will block forever if acquiring the semaphore would cause its maximum number of semaphore to be exceeded.

After processing a request, any semaphores acquired by the process but not explicitly released will be released automatically and a warning will be generated.

请求处理完会自动释放。

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操作系统层面上，参见sem_close：

All open named semaphores are automatically closed on process termination, or upon execve(2).