HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)

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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 parame-

ter (see signal(5)) will be set to value. If

SA_SIGINFO is not set for signo, then signo, but not neces-

sarily 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.

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 invalidor unsupported signal number.

[EPERM] The process does not have the appropriate privilege to send the signal to the receiving

process.

[ESRCH] The process pid does not exist.