假定信号在close系统调用设置errno变量到其返回之前这一极小的时间片段内生成。
Suppose a signal is generated during the very small time gap between setting the errno variable by the close system call and its return.
同步调用可以通过编程来实现，但带有超时设置，如果调用在一定的时间内未返回，调用Web Services可能取消锁定，从而从系统退出。
Synchronous calls can be programmed, but with timeouts so that if the call can't come back in a certain time, the calling Web service can be unlocked to exit from the system.
truss返回系统调用的列表、执行调用耗费的总时间、调用的次数和任何发现的问题。
Truss returns a list of the system calls, the total time spent executing the call, the number of calls, and any errors found.
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