sigwait(2) select a set of signals


Lb libc


In signal.h Ft int Fn sigwait const sigset_t * restrict set int * restrict sig


The Fn sigwait system call selects a set of signals, specified by Fa set . If none of the selected signals are pending, Fn sigwait waits until one or more of the selected signals has been generated. Then Fn sigwait atomically clears one of the selected signals from the set of pending signals (for the process or for the current thread) and sets the location pointed to by Fa sig to the signal number that was cleared.

The signals specified by Fa set should be blocked at the time of the call to Fn sigwait .

If more than one thread is using Fn sigwait to wait for the same signal, no more than one of these threads will return from Fn sigwait with the signal number. If more than a single thread is blocked in Fn sigwait for a signal when that signal is generated for the process, it is unspecified which of the waiting threads returns from Fn sigwait . If the signal is generated for a specific thread, as by Fn pthread_kill , only that thread will return.

Should any of the multiple pending signals in the range SIGRTMIN to SIGRTMAX be selected, it will be the lowest numbered one. The selection order between realtime and non-realtime signals, or between multiple pending non-realtime signals, is unspecified.


The Fn sigwait function is implemented as a wrapper around the Fn __sys_sigwait system call, which retries the call on Er EINTR error.


If successful, Fn sigwait returns 0 and sets the location pointed to by Fa sig to the cleared signal number. Otherwise, an error number is returned.


The Fn sigwait system call will fail if:

The Fa set argument specifies one or more invalid signal numbers.


The Fn sigwait function conforms to St -p1003.1-96 .