sigqueue.2 (2010 09)
s
sigqueue(2) sigqueue(2)
NAME
sigqueue() - queue a signal to a process
SYNOPSIS
#include <signal.h>
int sigqueue(pid_t pid, int signo, const union sigval value);
DESCRIPTION
The sigqueue() system call causes the signal specified by signo to be sent with the value specified by
value to the process specified by pid.Ifsigno is zero (the null signal), error checking is performed but no
signal is actually sent. The null signal can be used to check the validity of pid .
The conditions required for a process to have permission to queue a signal to another process are the
same as for the
kill() system call.
The
sigqueue() system call returns immediately. If
SA_SIGINFO is set for signo at the receiving pro-
cess (see sigqueue (2)) and if resources are available to queue the signal, the signal will be queued and
sent to the receiving process. When the signal is delivered or accepted, the field si_value of the siginfo
parameter (see signal (5)) will be set to value. If
SA_SIGINFO is not set for signo, then signo , but not
necessarily value , will be sent at least once to the receiving process.
If the value of pid causes signo to be generated for the sending process, and if signo is not blocked, either
signo or at least one pending unblocked signal will be delivered to the sending process before the
sigqueue() system call returns. Should any of multiple pending signals in the range SIGRTMIN to
SIGRTMAX be selected for delivery or acceptance, it will be the lowest numbered one. The selection order
between realtime and non-realtime signals, or between multiple pending non-realtime signals, is
unspecified.
Application Usage
Threads Considerations
sigqueue() can be used to post signals to another process but can not be used to post signals to a
specific thread in another process.
If the value of pid causes signo to be generated for the sending process, and if signo is not blocked for the
calling thread and if no other thread has signo unblocked or is waiting in a
sigwait()
function for
signo, either signo or at least one pending unblocked signal will be delivered to the calling thread before
the
sigqueue() function returns.
LWP Considerations
Signals can not be posted to specific Lightweight Processes (LWPs) in another process.
Security Restrictions
Some or all of the actions associated with this system call are subject to compartmental restrictions. See
compartments (5) for more information about compartmentalization on systems that support that feature.
Compartmental restrictions can be overridden if the process possesses the
PRIV_COMMALLOWED
privilege (COMMALLOWED). Processes owned by the superuser may not have this privilege. Processes
owned by any user may have this privilege, depending on system configuration.
Some or all of the actions associated with this system call require one or more privileges. Processes owned
by the superuser have many, though not all, privileges. Processes owned by other users may have
privilege(s), depending on system configuration. See privileges (5) for more information about privileged
access on systems that support fine-grained privileges.
RETURN VALUE
Upon successful completion, the specified signal will be queued, and the sigqueue() function returns a
value of 0 (zero). Otherwise, a value of -1 is returned, and errno is set to indicate the error.
ERRORS
sigqueue() fails and no signal is sent if any of the following conditions occur:
[EAGAIN] No resources are available to queue the signal. The process has already queued
{SIGQUEUE_MAX} signals that are still pending at the receiver(s), or a systemwide
resource limit has been exceeded.
[EINVAL] The value of the signo argument is an invalid or unsupported signal number.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1