diff options
Diffstat (limited to 'share/man/man9/rmlock.9')
| -rw-r--r-- | share/man/man9/rmlock.9 | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/share/man/man9/rmlock.9 b/share/man/man9/rmlock.9 index e99661d..2e68b07 100644 --- a/share/man/man9/rmlock.9 +++ b/share/man/man9/rmlock.9 @@ -35,6 +35,7 @@ .Nm rm_init_flags , .Nm rm_destroy , .Nm rm_rlock , +.Nm rm_try_rlock , .Nm rm_wlock , .Nm rm_runlock , .Nm rm_wunlock , @@ -53,6 +54,8 @@ .Fn rm_destroy "struct rmlock *rm" .Ft void .Fn rm_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" +.Ft int +.Fn rm_try_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" .Ft void .Fn rm_wlock "struct rmlock *rm" .Ft void @@ -84,14 +87,16 @@ Although reader/writer locks look very similar to locks, their usage pattern is different. Reader/writer locks can be treated as mutexes (see .Xr mutex 9 ) -with shared/exclusive semantics. +with shared/exclusive semantics unless initialized with +.Dv RM_SLEEPABLE . Unlike .Xr sx 9 , an .Nm can be locked while holding a non-spin mutex, and an .Nm -cannot be held while sleeping. +cannot be held while sleeping, again unless initialized with +.Dv RM_SLEEPABLE . The .Nm locks have full priority propagation like mutexes. @@ -135,6 +140,13 @@ to ignore this lock. .It Dv RM_RECURSE Allow threads to recursively acquire exclusive locks for .Fa rm . +.It Dv RM_SLEEPABLE +Allow writers to sleep while holding the lock. +Readers must not sleep while holding the lock and can avoid to sleep on +taking the lock by using +.Fn rm_try_rlock +instead of +.Fn rm_rlock . .El .It Fn rm_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" Lock @@ -161,6 +173,16 @@ access on .Fa rm . This is called .Dq "recursing on a lock" . +.It Fn rm_try_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" +Try to lock +.Fa rm +as a reader. +.Fn rm_try_rlock +will return 0 if the lock cannot be acquired immediately; +otherwise the lock will be acquired and a non-zero value will be returned. +Note that +.Fn rm_try_rlock +may fail even while the lock is not currently held by a writer. .It Fn rm_wlock "struct rmlock *rm" Lock .Fa rm @@ -217,6 +239,10 @@ The .Nm implementation is currently not optimized for single processor systems. .Pp +.Fn rm_try_rlock +can fail transiently even when there is no writer, while another reader +updates the state on the local CPU. +.Pp The .Nm implementation uses a single per CPU list shared by all |
