php_sem_ffi.php

<?php

$ffi = FFI::cdef(<<<'EOD'
    void *sem_open(const char *name, int oflag, int mode, int value);
    int sem_post(void *sem);
    int sem_wait(void *sem);
    int sem_getvalue(void *sem, int *sval);
    int sem_unlink(const char *name);
    int sem_close(void *sem);
EOD
);

$pid = getmypid();

$O_CREAT = 0x0040;
$sem = $ffi->sem_open('test_sem', $O_CREAT, 0644, 1);
$sem_val = $ffi->new('int');

while (true) {
    $ffi->sem_getvalue($sem, FFI::addr($sem_val));
    $ffi->sem_wait($sem);
    printf("%d acquired lock, sem_val was %d\n", $pid, $sem_val->cdata);
    $ffi->sem_post($sem);
}