DragonFly On-Line Manual Pages

CONDVAR(9)	      DragonFly Kernel Developer's Manual	    CONDVAR(9)


condvar, cv_init, cv_destroy, cv_wait, cv_wait_sig, cv_timedwait, cv_timedwait_sig, cv_signal, cv_broadcast, cv_broadcastpri -- kernel con- dition variable


#include <sys/param.h> #include <sys/systm.h> #include <sys/condvar.h> void cv_init(struct cv *cvp, const char *desc); void cv_destroy(struct cv *cvp); void cv_wait(struct cv *cvp, struct lock *l); int cv_wait_sig(struct cv *cvp, struct lock *l); int cv_timedwait(struct cv *cvp, struct lock *l, int timo); int cv_timedwait_sig(struct cv *cvp, struct lock *l, int timo); void cv_signal(struct cv *cvp); void cv_broadcast(struct cv *cvp); void cv_broadcastpri(struct cv *cvp, int pri);


Condition variables are used in conjunction with locks to wait for condi- tions to occur. Condition variables are created with cv_init(), where cvp is a pointer to space for a struct cv, and desc is a pointer to a null-terminated character string that describes the condition variable. Condition variables are destroyed with cv_destroy(). Threads wait on condition variables by calling cv_wait(), cv_wait_sig(), cv_timedwait(), or cv_timedwait_sig(). Threads unblock waiters by calling cv_signal() to unblock one waiter, or cv_broadcast() or cv_broadcastpri() to unblock all waiters. cv_broadcastpri() is a synonym for cv_broadcast() in DragonFly and discards the pri parameter. A thread must hold l before calling cv_wait(), cv_wait_sig(), cv_timedwait(), or cv_timedwait_sig(). When a thread waits on a condi- tion, l is atomically released before the thread is blocked, then atomi- cally reacquired before the function call returns. All waiters must pass the same l in conjunction with cvp. When cv_wait(), cv_wait_sig(), cv_timedwait(), and cv_timedwait_sig() unblock, their calling threads are made runnable. cv_timedwait() and cv_timedwait_sig() wait for at most timo / hz seconds before being unblocked and returning EWOULDBLOCK; otherwise, they return 0. cv_wait_sig() and cv_timedwait_sig() return prematurely with a value of EINTR or ERESTART if a signal is caught, or 0 if signaled via cv_signal() or cv_broadcast().


Condition variables exist primarily for code imported from other systems; for DragonFly code, the tsleep() / wakeup() family of functions should be used instead. Condition variables can currently only release lockmgr(9) locks.


If successful, cv_wait_sig(), cv_timedwait(), and cv_timedwait_sig() return 0. Otherwise, a non-zero error code is returned.


Condition variables are implemented in /sys/kern/kern_condvar.c. The public interface and structure is found in /sys/sys/condvar.h.


locking(9), lockmgr(9), tsleep(9)


Condition variables appeared in DragonFly 2.7.


This manual page was written by Jason Evans for FreeBSD. DragonFly 3.9 August 11, 2011 DragonFly 3.9