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Add to the mask of signals to block


#include <unix.h>

int sigblock( int mask );


A bitmask of the signals that you want to block.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The sigblock() function adds the signals specified in mask to the set of signals currently being blocked from delivery. Signals are blocked if the appropriate bit in mask is a 1; the macro sigmask() is provided to construct the mask for a given signum. The sigblock() returns the previous mask. You can restore the previous mask by calling sigsetmask().

In normal usage, a signal is blocked using sigblock(). To begin a critical section, variables modified on the occurrence of the signal are examined to determine that there's no work to be done, and the process pauses awaiting work by using sigpause() with the mask returned by sigblock().

It isn't possible to block SIGKILL, SIGSTOP, or SIGCONT; this restriction is silently imposed by the system.


The previous set of masked signals.



Cancellation point No
Interrupt handler No
Signal handler Yes
Thread No


Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system libraries or in multithreaded applications is unsupported.

See also:

kill(), pthread_sigmask(), sigaction(), sigmask(), signal(), sigpause(), sigprocmask(), sigsetmask(), sigunblock()