sigwaitinfo(2) - Linux manual page (original) (raw)

sigwaitinfo(2) System Calls Manual sigwaitinfo(2)

NAME top

   sigwaitinfo, sigtimedwait, rt_sigtimedwait - synchronously wait
   for queued signals

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <signal.h>**

   **int sigwaitinfo(const sigset_t *restrict** _set_**,**
                   **siginfo_t *_Nullable restrict** _info_**);**
   **int sigtimedwait(const sigset_t *restrict** _set_**,**
                   **siginfo_t *_Nullable restrict** _info_**,**
                   **const struct timespec *restrict** _timeout_**);**

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   **sigwaitinfo**(), **sigtimedwait**():
       _POSIX_C_SOURCE >= 199309L

DESCRIPTION top

   **sigwaitinfo**() suspends execution of the calling thread until one
   of the signals in _set_ is pending (If one of the signals in _set_ is
   already pending for the calling thread, **sigwaitinfo**() will return
   immediately.)

   **sigwaitinfo**() removes the signal from the set of pending signals
   and returns the signal number as its function result.  If the _info_
   argument is not NULL, then the buffer that it points to is used to
   return a structure of type _siginfot_ (see [sigaction(2)](../man2/sigaction.2.html)) containing
   information about the signal.

   If multiple signals in _set_ are pending for the caller, the signal
   that is retrieved by **sigwaitinfo**() is determined according to the
   usual ordering rules; see [signal(7)](../man7/signal.7.html) for further details.

   **sigtimedwait**() operates in exactly the same way as **sigwaitinfo**()
   except that it has an additional argument, _timeout_, which
   specifies the interval for which the thread is suspended waiting
   for a signal.  (This interval will be rounded up to the system
   clock granularity, and kernel scheduling delays mean that the
   interval may overrun by a small amount.)  This argument is a
   **timespec**(3) structure.

   If both fields of this structure are specified as 0, a poll is
   performed: **sigtimedwait**() returns immediately, either with
   information about a signal that was pending for the caller, or
   with an error if none of the signals in _set_ was pending.

RETURN VALUE top

   On success, both **sigwaitinfo**() and **sigtimedwait**() return a signal
   number (i.e., a value greater than zero).  On failure both calls
   return -1, with _[errno](../man3/errno.3.html)_ set to indicate the error.

ERRORS top

   **EAGAIN** No signal in _set_ became pending within the _timeout_ period
          specified to **sigtimedwait**().

   **EINTR** The wait was interrupted by a signal handler; see
          [signal(7)](../man7/signal.7.html).  (This handler was for a signal other than one
          of those in _set_.)

   **EINVAL** _timeout_ was invalid.

VERSIONS top

C library/kernel differences On Linux, sigwaitinfo() is a library function implemented on top of sigtimedwait().

   The glibc wrapper functions for **sigwaitinfo**() and **sigtimedwait**()
   silently ignore attempts to wait for the two real-time signals
   that are used internally by the NPTL threading implementation.
   See [nptl(7)](../man7/nptl.7.html) for details.

   The original Linux system call was named **sigtimedwait**().  However,
   with the addition of real-time signals in Linux 2.2, the fixed-
   size, 32-bit _sigsett_ type supported by that system call was no
   longer fit for purpose.  Consequently, a new system call,
   **rt_sigtimedwait**(), was added to support an enlarged _sigsett_ type.
   The new system call takes a fourth argument, _sizet sigsetsize_,
   which specifies the size in bytes of the signal set in _set_.  This
   argument is currently required to have the value _sizeof(sigsett)_
   (or the error **EINVAL** results).  The glibc **sigtimedwait**() wrapper
   function hides these details from us, transparently calling
   **rt_sigtimedwait**() when the kernel provides it.

STANDARDS top

   POSIX.1-2008.

HISTORY top

   POSIX.1-2001.

NOTES top

   In normal usage, the calling program blocks the signals in _set_ via
   a prior call to [sigprocmask(2)](../man2/sigprocmask.2.html) (so that the default disposition
   for these signals does not occur if they become pending between
   successive calls to **sigwaitinfo**() or **sigtimedwait**()) and does not
   establish handlers for these signals.  In a multithreaded program,
   the signal should be blocked in all threads, in order to prevent
   the signal being treated according to its default disposition in a
   thread other than the one calling **sigwaitinfo**() or
   **sigtimedwait**()).

   The set of signals that is pending for a given thread is the union
   of the set of signals that is pending specifically for that thread
   and the set of signals that is pending for the process as a whole
   (see [signal(7)](../man7/signal.7.html)).

   Attempts to wait for **SIGKILL** and **SIGSTOP** are silently ignored.

   If multiple threads of a process are blocked waiting for the same
   signal(s) in **sigwaitinfo**() or **sigtimedwait**(), then exactly one of
   the threads will actually receive the signal if it becomes pending
   for the process as a whole; which of the threads receives the
   signal is indeterminate.

   **sigwaitinfo**() or **sigtimedwait**(), can't be used to receive signals
   that are synchronously generated, such as the **SIGSEGV** signal that
   results from accessing an invalid memory address or the **SIGFPE**
   signal that results from an arithmetic error.  Such signals can be
   caught only via signal handler.

   POSIX leaves the meaning of a NULL value for the _timeout_ argument
   of **sigtimedwait**() unspecified, permitting the possibility that
   this has the same meaning as a call to **sigwaitinfo**(), and indeed
   this is what is done on Linux.

SEE ALSO top

   [kill(2)](../man2/kill.2.html), [sigaction(2)](../man2/sigaction.2.html), [signal(2)](../man2/signal.2.html), [signalfd(2)](../man2/signalfd.2.html), [sigpending(2)](../man2/sigpending.2.html),
   [sigprocmask(2)](../man2/sigprocmask.2.html), [sigqueue(3)](../man3/sigqueue.3.html), [sigsetops(3)](../man3/sigsetops.3.html), [sigwait(3)](../man3/sigwait.3.html),
   **timespec**(3), [signal(7)](../man7/signal.7.html), [time(7)](../man7/time.7.html)

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Linux man-pages 6.10 2024-07-23 sigwaitinfo(2)

Pages that refer to this page:clone(2), signalfd(2), sigsuspend(2), syscalls(2), timer_getoverrun(2), sigevent(3type), sigqueue(3), sigwait(3), nptl(7), signal(7), system_data_types(7), time(7)