请教一个SIGNAL的小问题

rainysky

如果我已经在一个信号处理函数里面，对于同类型的信号是自动BLOCK的，对吗？我在信号处理函数里面UNBLOCK这个信号，是否可以做到？一但UNBLOCK了，是不是可能造成这个信号处理函数嵌套调用？
呵呵，懒得自己写程序自己试了，请达人帮下忙？

rainysky

晕，还要自己顶。大概知道什么情况了。

What happens if another signal arrives when your signal handler function is running?

When the handler for a particular signal is invoked, that signal is normally blocked until the handler returns. That means that if two signals of the same kind arrive close together, the second one will be held until the first has been handled. (The handler can explicitly unblock the signal using sigprocmask, if you want to allow more signals of this type to arrive; see section Process Signal Mask.)

However, your handler can still be interrupted by delivery of another kind of signal. To avoid this, you can use the sa_mask member of the action structure passed to sigaction to explicitly specify which signals should be blocked while the signal handler runs. These signals are in addition to the signal for which the handler was invoked, and any other signals that are normally blocked by the process. See section Blocking Signals for a Handler.

Portability Note: Always use sigaction to establish a handler for a signal that you expect to receive asynchronously, if you want your program to work properly on System V Unix. On this system, the handling of a signal whose handler was established with signal automatically sets the signal's action back to SIG_DFL, and the handler must re-establish itself each time it runs. This practice, while inconvenient, does work when signals cannot arrive in succession. However, if another signal can arrive right away, it may arrive before the handler can re-establish itself. Then the second signal would receive the default handling, which could terminate the process.

lanying_wzw

答案是肯定的，不过一般没有这样的需求