(PECL sync >= 1.0.0)
SyncReaderWriter::readlock — Waits for a read lock
$wait = -1): boolObtains a read lock on a SyncReaderWriter object.
waitThe number of milliseconds to wait for a lock. A value of -1 is infinite.
成功时返回 true， 或者在失败时返回 false。
示例 #1 SyncReaderWriter::readlock() example
<?php
$readwrite = new SyncReaderWriter("FileCacheLock");
$readwrite->readlock();
/* ... */
$readwrite->readunlock();
?>