condvar, cv_init, cv_destroy, cv_wait, cv_wait_sig, cv_timedwait,
cv_timedwait_sig, cv_signal, cv_broadcast, cv_waitq_remove,
cv_waitq_empty, cv_wmesg -- kernel condition variable
#include <sys/param.h>
#include <sys/proc.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 mtx *mp);
int
cv_wait_sig(struct cv *cvp, struct mtx *mp);
int
cv_timedwait(struct cv *cvp, struct mtx *mp, int timo);
int
cv_timedwait_sig(struct cv *cvp, struct mtx *mp, int timo);
void
cv_signal(struct cv *cvp);
void
cv_broadcast(struct cv *cvp);
void
cv_waitq_remove(struct thread *td);
int
cv_waitq_empty(struct cv *cvp);
const char *
cv_wmesg(struct cv *cvp);
Condition variables are used in conjunction with mutexes to wait for conditions
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() to unblock all waiters.
cv_waitq_remove() removes a waiting thread from a condition variable wait
queue, if it is on one. cv_waitq_empty() reports whether there are any
waiters on cvp. cv_wmesg() returns the description string of cvp, as set
by the initial call to cv_init().
A thread must hold mp before calling cv_wait(), cv_wait_sig(),
cv_timedwait(), or cv_timedwait_sig(). When a thread waits on a condition,
mp is atomically released before the thread is blocked, then atomically
reacquired before the function call returns. All waiters must pass
the same mp in conjunction with cvp. A thread must hold mp while calling
cv_signal() or cv_broadcast(), even though it isn't passed as an argument.
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().
If successful, cv_wait_sig(), cv_timedwait(), and cv_timedwait_sig()
return 0. Otherwise, a non-zero error code is returned.
cv_waitq_empty() returns non-zero if there are no threads on the wait
queue; 0 otherwise.
cv_wmesg() returns the description string that was passed to cv_init().
cv_wait_sig() and cv_timedwait_sig() will fail if:
[EINTR] An unmasked signal was caught.
[ERESTART] A masked signal was caught.
cv_timedwait() and cv_timedwait_sig() will fail if:
[EWOULDBLOCK] Timeout expired.
msleep(9), mtx_pool(9), mutex(9), sema(9), sx(9)
FreeBSD 5.2.1 December 11, 2000 FreeBSD 5.2.1 [ Back ] |
