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20. Signals: Fundamental Concepts > The Signal Mask (Blocking Signal Delivery)

The Signal Mask (Blocking Signal Delivery)

For each process, the kernel maintains a signal mask—a set of signals whose delivery to the process is currently blocked. If a signal that is blocked is sent to a process, delivery of that signal is delayed until it is unblocked by being removed from the process signal mask. (In How the UNIX Signal Model Maps to Threads, we’ll see that the signal mask is actually a per-thread attribute, and that each thread in a multithreaded process can independently examine and modify its signal mask using the pthread_sigmask() function.)

A signal may be added to the signal mask in the following ways:

  • When a signal handler is invoked, the signal that caused its invocation can be automatically added to the signal mask. Whether or not this occurs depends on the flags used when the handler is established using sigaction().


  

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