thr_sigsetmask(3thread)

thr_sigsetmask -- change or examine the signal mask of a thread

Synopsis

   cc [options] -Kthread file
   
   #include <thread.h>
   

   int thr_sigsetmask(int how, const sigset_t *set, sigset_t *oset);

Description

thr_sigsetmask changes or examines the calling thread's signal mask according to the way how and set are set.

If there are any pending unblocked signals after the call to thr_sigsetmask, at least one of those signals will be delivered before the call to thr_sigsetmask returns.

In this implementation, changing the signal mask of the thread will also change the signal mask of the lightweight process (LWP) running the thread.

Parameters

how: SIG_BLOCK, SIG_UNBLOCK, or SIG_SETMASK
set: pointer to a set of signals to be blocked or unblocked
oset: pointer to the value of the previous signal mask (set by thr_sigsetmask)

how parameter

how determines how set is interpreted. Set how to one of the following values:

SIG_BLOCK: Add the set of signals denoted by set to the current signal mask
SIG_UNBLOCK: Remove the set of signals denoted by set from the current signal mask
SIG_SETMASK: Replace the current signal mask with the set of signals denoted by set

Note that 0 is not a valid value for how.

set parameter

set points to a set of signals to be blocked or unblocked (according to the value of how) in the current thread. set is usually constructed with the routines described on sigsetops(3C). If set is NULL, the value of how is not significant, and the thread's signal mask will not be changed.

It is not possible to block those signals that cannot be ignored (see sigaction(2)); this restriction is silently imposed by the system.

oset parameter

If oset is not NULL, thr_sigsetmask stores the value of the previous mask in that location. If set is NULL and oset is not NULL, oset will point to the value of the thread's current signal mask.

Return values

thr_sigsetmask returns zero for success and an error number for failure, as described below.

If thr_sigsetmask fails, the thread's signal mask is not changed.

Errors

If any of the following conditions occurs, thr_sigsetmask returns the corresponding value:

EINVAL: The value of how is not equal to one of the defined values.

Portability considerations

Threads should use thr_sigsetmask rather than sigprocmask(2). In some implementations, sigprocmask can be trapped and behaves identically to thr_sigsetmask, but for portability, thr_sigsetmask should be used.

Performance considerations

In this implementation, an application running multiplexed threads with different signal masks can observe a performance degradation. Therefore, for optimal performance, all multiplexing threads in a process should use the same signal mask. Applications needing threads that will run frequently with signal masks different from other threads in the process should consider creating those threads as bound threads for better performance.

Style considerations

The preferred coding style is to mask all signals and use sigwait synchronously.

References

Intro(3thread), kill(2), sigaction(2), signal(5), sigprocmask(2), sigsend(2), sigsetops(3C), sigwait(2), thr_kill(3thread)