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PTHREAD_SIGNAL

PTHREAD_SIGNAL

Section: C Library Functions (3) Updated: LinuxThreads
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NAME

pthread_sigmask, pthread_kill, sigwait - handling of signals in threads

 

SYNOPSIS

#include <pthread.h>
#include <signal.h>

int pthread_sigmask(int how, const sigset_t *newmask, sigset_t *oldmask);

int pthread_kill(pthread_t thread, int signo);

int sigwait(const sigset_t *set, int *sig);

 

DESCRIPTION

pthread_sigmask changes the signal mask for the calling thread as described by the how and newmask arguments. If oldmask is not NULL, the previous signal mask is stored in the location pointed to by oldmask.

The meaning of the how and newmask arguments is the same as for sigprocmask(2). If how is SIG_SETMASK, the signal mask is set to newmask. If how is SIG_BLOCK, the signals specified to newmask are added to the current signal mask. If how is SIG_UNBLOCK, the signals specified to newmask are removed from the current signal mask.

Recall that signal masks are set on a per-thread basis, but signal actions and signal handlers, as set with sigaction(2), are shared between all threads.

pthread_kill send signal number signo to the thread thread. The signal is delivered and handled as described in kill(2).

sigwait suspends the calling thread until one of the signals in set is delivered to the calling thread. It then stores the number of the signal received in the location pointed to by sig and returns. The signals in set must be blocked and not ignored on entrance to sigwait. If the delivered signal has a signal handler function attached, that function is not called.

 

CANCELLATION

sigwait is a cancellation point.

 

RETURN VALUE

On success, 0 is returned. On failure, a non-zero error code is returned.

 

ERRORS

The pthread_sigmask function returns the following error codes on error:

EINVAL
how is not one of SIG_SETMASK, SIG_BLOCK, or SIG_UNBLOCK

EFAULT
newmask or oldmask point to invalid addresses

The pthread_kill function returns the following error codes on error:

EINVAL
signo is not a valid signal number

ESRCH
the thread thread does not exist (e.g. it has already terminated)

The sigwait function never returns an error.

 

AUTHOR

Xavier Leroy <Xavier.Leroy@inria.fr>

 

SEE ALSO

sigprocmask(2), kill(2), sigaction(2), sigsuspend(2).

 

NOTES

For sigwait to work reliably, the signals being waited for must be blocked in all threads, not only in the calling thread, since otherwise the POSIX semantics for signal delivery do not guarantee that it's the thread doing the sigwait that will receive the signal. The best way to achieve this is block those signals before any threads are created, and never unblock them in the program other than by calling sigwait.

 

BUGS

Signal handling in LinuxThreads departs significantly from the POSIX standard. According to the standard, ``asynchronous'' (external) signals are addressed to the whole process (the collection of all threads), which then delivers them to one particular thread. The thread that actually receives the signal is any thread that does not currently block the signal.

In LinuxThreads, each thread is actually a kernel process with its own PID, so external signals are always directed to one particular thread. If, for instance, another thread is blocked in sigwait on that signal, it will not be restarted.

The LinuxThreads implementation of sigwait installs dummy signal handlers for the signals in set for the duration of the wait. Since signal handlers are shared between all threads, other threads must not attach their own signal handlers to these signals, or alternatively they should all block these signals (which is recommended anyway -- see the Notes section).


 

Index

NAME
SYNOPSIS
DESCRIPTION
CANCELLATION
RETURN VALUE
ERRORS
AUTHOR
SEE ALSO
NOTES
BUGS

This document was created by man2html, using the manual pages.
Time: 22:27:19 GMT, April 16, 2011