sigqueue - queue a signal and data to a process
#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
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
(either 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 argument to the handler. Furthermore, the
si_code field of that
structure will be set to
SI_QUEUE.
On success,
sigqueue() returns 0, indicating that the signal was
successfully queued to the receiving process. Otherwise, -1 is returned and
errno is set to indicate the error.
- 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.
sigqueue() and the underlying
rt_sigqueueinfo() system call first
appeared in Linux 2.2.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
sigqueue () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008.
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.
On Linux,
sigqueue() is implemented using the
rt_sigqueueinfo(2)
system call. The system call differs in its third argument, which is the
siginfo_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 initialized 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() */
kill(2),
rt_sigqueueinfo(2),
sigaction(2),
signal(2),
pthread_sigqueue(3),
sigwait(3),
signal(7)