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-
cv_init(struct cv *cvp, const char *desc);
cv_destroy(struct cv *cvp);
cv_wait(struct cv *cvp, struct lock *l);
cv_wait_sig(struct cv *cvp, struct lock *l);
cv_timedwait(struct cv *cvp, struct lock *l, int timo);
cv_timedwait_sig(struct cv *cvp, struct lock *l, int timo);
cv_signal(struct cv *cvp);
cv_broadcast(struct cv *cvp);
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()
Condition variables exist primarily for code imported from other systems;
for DragonFly code, the tsleep() / wakeup() family of functions should be
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 4.1 August 11, 2011 DragonFly 4.1