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upon further reflection, rw_write_held() actually seems to be safe 

for check that the write lock is not currently held by current lwp - current
lwp can't acquire the rwlock even when preempted
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jdolecek 2018-12-10 20:12:36 +00:00
parent 19787ecf98
commit 77adaba307
1 changed files with 5 additions and 1 deletions
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6
share/man/man9/rwlock.9
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@ -1,4 +1,4 @@
.\" $NetBSD: rwlock.9,v 1.18 2018/12/10 19:21:56 jdolecek Exp $
.\" $NetBSD: rwlock.9,v 1.19 2018/12/10 20:12:36 jdolecek Exp $
.\"
.\" Copyright (c) 2006, 2007, 2009 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -188,6 +188,10 @@ must never be used to make locking decisions at run time:
they are provided only for diagnostic purposes.
They are also not atomic, hence they should only be used to assert
that lock is held.
The only exception is
.Fn rw_write_held ,
which can be also used safely to assert that write lock is NOT currently
held by current lwp.
.El
.Sh PERFORMANCE CONSIDERATIONS
RW locks are subject to high cache contention on multiprocessor systems,