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- Note that cv_has_waiters() can only be used to assert that there are

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waiters sleeping non-interruptably (i.e., in cv_wait()). Prompted by
  a discussion with pooka@.
- Minor cosmetic changes.
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ad 2007-03-29 17:40:36 +00:00
parent 5714ab2718
commit 4d04f2f136
1 changed files with 20 additions and 27 deletions
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47
share/man/man9/condvar.9
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@ -1,4 +1,4 @@
.\" $NetBSD: condvar.9,v 1.8 2007/02/05 15:04:21 ad Exp $
.\" $NetBSD: condvar.9,v 1.9 2007/03/29 17:40:36 ad Exp $
.\"
.\" Copyright (c) 2006, 2007 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -34,7 +34,7 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd February 4, 2007
.Dd March 27, 2007
.Dt CONDVAR 9
.Os
.Sh NAME
@ -48,7 +48,6 @@
.Nm cv_timedwait_sig ,
.Nm cv_signal ,
.Nm cv_broadcast ,
.Nm cv_wakeup ,
.Nm cv_has_waiters
.Nd condition variables
.Sh SYNOPSIS
@ -69,9 +68,7 @@
.Fn cv_signal "kcondvar_t *cv"
.Ft void
.Fn cv_broadcast "kcondvar_t *cv"
.Ft void
.Fn cv_wakeup "kcondvar_t *cv"
.Ft int
.Ft bool
.Fn cv_has_waiters "kcondvar_t *cv"
.Sh DESCRIPTION
Condition variables (CVs) are used in the kernel to synchronize access
@ -199,23 +196,22 @@ The mutex passed to the wait function
.Po Fa mtx Pc
must also be held when calling
.Fn cv_broadcast .
.It Fn cv_wakeup "cv"
.Pp
As per
.Fn cv_broadcast ,
but the interlock
.Po Fa mtx Pc
need not be held.
Use of this method is discouraged it is more costly to execute than
.Fn cv_broadcast
or
.Fn cv_signal .
.It Fn cv_has_waiters "cv"
.Pp
Return non-zero if one or more LWPs are waiting on the specified condition
variable.
Return
.Dv true
if one or more LWPs are waiting on the specified condition variable.
.Pp
.Fn cv_has_waiters
should only be used when making diagnostic assertions.
cannot test reliably for interruptable waits.
It should only be used to test for non-interruptable waits
made using
.Fn cv_wait .
.Pp
.Fn cv_has_waiters
should only be used when making diagnostic assertions, and must
be called while holding the interlocking mutex passed to
.Fn cv_wait .
.El
.Sh EXAMPLES
.Bd -literal
@ -228,16 +224,16 @@ Consuming a resource:
mutex_enter(\*[Am]res-\*[Gt]mutex);
/*
* Wait for the resource to become available, and take
* ownership of it.
* Wait for the resource to become available.
*/
while (res-\*[Gt]state == BUSY)
cv_wait(\*[Am]res-\*[Gt]condvar, \*[Am]res-\*[Gt]mutex);
res-\*[Gt]state = BUSY;
/*
* It's now available to us.
* It's now available to us. Take ownership of the
* resource, and consume it.
*/
res-\*[Gt]state = BUSY;
mutex_exit(\*[Am]res-\*[Gt]mutex);
consume(res);
@ -280,6 +276,3 @@ describes the public interface.
.Sh HISTORY
The CV primitives first appeared in
.Nx 5.0 .
They are modelled after similar primitives implemented in
Sun Solaris, and have been extended for
.Nx .