Threads: Further Details

33.2 Threads and Signals

The differences between the signal and thread models mean that combining signals and threads is complex, and should be avoided whenever possible.

signal 在设计的时候根本没有考虑 thread 的使用，不要混用两者

• Signal actions are process-wide. If any unhandled signal whose default action is stop or terminate is delivered to any thread in a process, then all of the threads in the process are stopped or terminated.
• Signal dispositions are process-wide;
• A signal may be directed to either the process as a whole or to a specific thread.
• When a signal is delivered to a multithreaded process that has established a signal handler, the kernel arbitrarily selects one thread in the process to which to deliver the signal and invokes the handler in that thread.
• The signal mask is per-thread.
• The kernel maintains a record of the signals that are pending for the process as a whole, as well as a record of the signals that are pending for each thread. A call to sigpending() returns the union of the set of signals that are pending for the process and those that are pending for the calling thread. In a newly created thread, the per-thread set of pending signals is initially empty. A thread-directed signal can be delivered only to the target thread. If the thread is blocking the signal, it will remain pending until the thread unblocks the signal (or terminates).

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