sigqueue(3)

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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   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.

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