CND(3) | Library Functions Manual | CND(3)

# NAME

`cnd` —
condition variable functions

# LIBRARY

POSIX Threads Library (libpthread, -lpthread)

# SYNOPSIS

`#include <threads.h>`

int
`cnd_broadcast`(cnd_t *cond);

void
`cnd_destroy`(cnd_t *cond);

int
`cnd_init`(cnd_t *cond);

int
`cnd_signal`(cnd_t *cond);

int
`cnd_timedwait`(cnd_t * __restrict cond, mtx_t * __restrict mtx, const struct timespec * __restrict ts);

int
`cnd_wait`(cnd_t *cond, mtx_t *mtx);

# DESCRIPTION

The `cnd_broadcast`() function unblocks all threads that are blocked on a condition variable cond at the time of the call. If no thread is blocked on the cond condition variable at the time of the call, the function does nothing and returns success.

The `cnd_destroy`() function destroys the cond condition variable.

The `cnd_init`() function initializes a new cond variable.

The `cnd_signal`() function unblock one thread that currently waits on the cond variable. If there are no threads blocked, `cnd_signal`() does nothing and returns success.

The `cnd_timedwait`() function atomically unlocks the mutex mtx and blocks on the condition variable cond until a thread is signalled by a call to `cnd_signal`() or `cnd_broadcast`() or timeout ts has been reached. The ts parameter is specified as `TIME_UTC` based calendar time. If the mutex is not locked by the calling thread then behavior is undefined.

The `cnd_wait`() function atomically unlocks the mutex mtx and tries to block on the conditional variable cond until a thread is signalled by a call to `cnd_signal`() or `cnd_broadcast`(). The mtx mutex is locked again before the function returns. If the mutex is not locked by the calling thread then behavior is undefined.

# RETURN VALUES

The `cnd_broadcast`() function returns `thrd_success` on success or `thrd_error` on failure.

The `cnd_destroy`() function returns no value.

The `cnd_init`() function returns `thrd_success` on success or `thrd_error` on failure.

The `cnd_signal`() function returns `thrd_success` on success or `thrd_error` on failure.

The `cnd_timedwait`() function returns `thrd_success` on success, otherwise `thrd_timedout` to indicate that system time has reached or exceeded the time specified in `ts`, or `thrd_error` on failure.

The `cnd_wait`() function returns `thrd_success` on success or `thrd_error` on failure.

# SEE ALSO

pthread_cond(3), threads(3)

# STANDARDS

The `cnd` interface conforms to ISO/IEC 9899:2011 (“ISO C11”).

# HISTORY

This interface first appeared in NetBSD 9.

# AUTHORS

Kamil Rytarowski <kamil@NetBSD.org>

October 16, 2016 | NetBSD 9.5