pthread_rwlock_rdlock may fail if the maximum number of read locks (implementation defined) for the lock has been exceeded.

如果超过了最大读锁数量（由实现定义），pthread_rwlock_rdlock 可能会失败。

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Conversely, if an exclusive lock was able to be acquired, concurrent applications would not be able to access the file and could fail with a lock time-out.

相反地，如果能够获得互斥型锁，那么并发应用程序就无法访问文件，并因为锁超时失败。

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A lock can fail, for example, if files on the target volume are currently opened by other programs.

锁定会有失败的情况，例如，当目标卷上的文件正被其他的程序打开。

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