NAME

       sigqueue - queue a signal and data to a process

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 (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.

RETURN VALUE

       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.

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.

VERSIONS

       sigqueue() and the underlying rt_sigqueueinfo() system call first appeared in Linux 2.2.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────┬───────────────┬─────────┐
       │Interface  │ Attribute     │ Value   │
       ├───────────┼───────────────┼─────────┤
       │sigqueue() │ Thread safety │ MT-Safe │
       └───────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

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.

   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 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() */

SEE ALSO

       kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2), pthread_sigqueue(3), sigwait(3), signal(7)

COLOPHON

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