INTRO (9) NetBSD Kernel Developer's Manual INTRO (9) NAME ...

CONDVAR(9) NetBSD Kernel Developer’s Manual CONDVAR(9)cv_broadcast(cv)Aw aken all LWPs waiting on the specified condition variable. The mutex passed to the wait function( mtx )must also be held when calling cv_broadcast().cv_has_waiters(cv)Return true if one or more LWPs are waiting on the specified condition variable.cv_has_waiters() cannot test reliably for interruptable waits. It should only be used to test fornon-interruptable waits made using cv_wait().cv_has_waiters() should only be used when making diagnostic assertions, and must be calledwhile holding the interlocking mutex passed to cv_wait().EXAMPLESConsuming a resource:/∗∗ Lock the resource. Its mutex will also serve as the∗ interlock.∗/mutex_enter(&res->mutex);/∗∗ Wait for the resource to become available.∗/while (res->state == BUSY)cv_wait(&res->condvar, &res->mutex);/∗∗ It’s now available to us.∗ resource, and consume it.∗/res->state = BUSY;mutex_exit(&res->mutex);consume(res);Take ownership of theReleasing a resource for the next consumer to use:mutex_enter(&res->mutex);res->state = IDLE;cv_signal(&res->condvar);mutex_exit(&res->mutex);CODE REFERENCESThis section describes places within the NetBSD source tree where code implementing condition variablescan be found. All pathnames are relative to /usr/src.The core of the CV implementation is in sys/kern/kern_condvar.c.The header file sys/sys/condvar.h describes the public interface.NetBSD 3.0 June 4, 2008 3