sigqueue(3) Library Functions Manual sigqueue(3)
NAME
sigqueue - queue a signal and data to a process
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <signal.h>
int sigqueue(pid_t pid, int sig, const union sigval value);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sigqueue():
_POSIX_C_SOURCE >= 199309L
DESCRIPTION
sigqueue() sends the signal specified in sig to the process whose PID is
given in pid. The permissions required to send a signal are the same as
for kill(2). As with kill(2), the null signal (0) can be used to check
if a process with a given PID exists.
The value argument is used to specify an accompanying item of data (ei-
ther an integer or a pointer value) to be sent with the signal, and has
the following type:
union sigval {
int sival_int;
void *sival_ptr;
};
If the receiving process has installed a handler for this signal using
the SA_SIGINFO flag to sigaction(2), then it can obtain this data via
the si_value field of the siginfo_t structure passed as the second argu-
ment to the handler. Furthermore, the si_code field of that structure
will be set to SI_QUEUE.
RETURN VALUE
On success, sigqueue() returns 0, indicating that the signal was suc-
cessfully queued to the receiving process. Otherwise, -1 is returned
and errno is set to indicate the error.
ERRORS
EAGAIN The limit of signals which may be queued has been reached. (See
signal(7) for further information.)
EINVAL sig was invalid.
EPERM The process does not have permission to send the signal to the
receiving process. For the required permissions, see kill(2).
ESRCH No process has a PID matching pid.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ sigqueue() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
VERSIONS
C library/kernel differences
On Linux, sigqueue() is implemented using the rt_sigqueueinfo(2) system
call. The system call differs in its third argument, which is the sig-
info_t structure that will be supplied to the receiving process's signal
handler or returned by the receiving process's sigtimedwait(2) call.
Inside the glibc sigqueue() wrapper, this argument, uinfo, is initial-
ized as follows:
uinfo.si_signo = sig; /* Argument supplied to sigqueue() */
uinfo.si_code = SI_QUEUE;
uinfo.si_pid = getpid(); /* Process ID of sender */
uinfo.si_uid = getuid(); /* Real UID of sender */
uinfo.si_value = val; /* Argument supplied to sigqueue() */
STANDARDS
POSIX.1-2008.
HISTORY
Linux 2.2. POSIX.1-2001.
NOTES
If this function results in the sending of a signal to the process that
invoked it, and that signal was not blocked by the calling thread, and
no other threads were willing to handle this signal (either by having it
unblocked, or by waiting for it using sigwait(3)), then at least some
signal must be delivered to this thread before this function returns.
SEE ALSO
kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2),
pthread_sigqueue(3), sigwait(3), signal(7)
Linux man-pages 6.9.1 2024-05-02 sigqueue(3)
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