| locking.9 (233422) | locking.9 (233648) |
|---|---|
| 1.\" Copyright (c) 2007 Julian Elischer (julian - freebsd org ) 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. --- 8 unchanged lines hidden (view full) --- 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" | 1.\" Copyright (c) 2007 Julian Elischer (julian - freebsd org ) 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. --- 8 unchanged lines hidden (view full) --- 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" |
| 25.\" $FreeBSD: head/share/man/man9/locking.9 233422 2012-03-24 13:37:57Z joel $ | 25.\" $FreeBSD: head/share/man/man9/locking.9 233648 2012-03-29 05:02:12Z eadler $ |
| 26.\" 27.Dd November 3, 2010 28.Dt LOCKING 9 29.Os 30.Sh NAME 31.Nm locking 32.Nd kernel synchronization primitives 33.Sh DESCRIPTION --- 43 unchanged lines hidden (view full) --- 77since they should only read the protected data. 78A thread with exclusive access is known as a 79.Em writer 80since it may modify protected data. 81.Pp 82Reader/writer locks can be treated as mutexes (see above and 83.Xr mutex 9 ) 84with shared/exclusive semantics. | 26.\" 27.Dd November 3, 2010 28.Dt LOCKING 9 29.Os 30.Sh NAME 31.Nm locking 32.Nd kernel synchronization primitives 33.Sh DESCRIPTION --- 43 unchanged lines hidden (view full) --- 77since they should only read the protected data. 78A thread with exclusive access is known as a 79.Em writer 80since it may modify protected data. 81.Pp 82Reader/writer locks can be treated as mutexes (see above and 83.Xr mutex 9 ) 84with shared/exclusive semantics. |
| 85More specifically, regular mutexes can be | 85More specifically, regular mutexes can be |
| 86considered to be equivalent to a write-lock on an 87.Em rw_lock. 88The 89.Em rw_lock 90locks have priority propagation like mutexes, but priority 91can be propagated only to an exclusive holder. 92This limitation comes from the fact that shared owners 93are anonymous. 94Another important property is that shared holders of 95.Em rw_lock 96can recurse, but exclusive locks are not allowed to recurse. | 86considered to be equivalent to a write-lock on an 87.Em rw_lock. 88The 89.Em rw_lock 90locks have priority propagation like mutexes, but priority 91can be propagated only to an exclusive holder. 92This limitation comes from the fact that shared owners 93are anonymous. 94Another important property is that shared holders of 95.Em rw_lock 96can recurse, but exclusive locks are not allowed to recurse. |
| 97This ability should not be used lightly and | 97This ability should not be used lightly and |
| 98.Em may go away. 99.Pp 100See 101.Xr rwlock 9 102for details. 103.Ss Read-mostly locks 104Mostly reader locks are similar to 105.Em reader/writer --- 11 unchanged lines hidden (view full) --- 117Shared/exclusive locks are similar to reader/writer locks; the main difference 118between them is that shared/exclusive locks may be held during unbounded sleep 119(and may thus perform an unbounded sleep). 120They are inherently less efficient than mutexes, reader/writer locks 121and read-mostly locks. 122They don't support priority propagation. 123They should be considered to be closely related to 124.Xr sleep 9 . | 98.Em may go away. 99.Pp 100See 101.Xr rwlock 9 102for details. 103.Ss Read-mostly locks 104Mostly reader locks are similar to 105.Em reader/writer --- 11 unchanged lines hidden (view full) --- 117Shared/exclusive locks are similar to reader/writer locks; the main difference 118between them is that shared/exclusive locks may be held during unbounded sleep 119(and may thus perform an unbounded sleep). 120They are inherently less efficient than mutexes, reader/writer locks 121and read-mostly locks. 122They don't support priority propagation. 123They should be considered to be closely related to 124.Xr sleep 9 . |
| 125In fact it could in some cases be | 125In fact it could in some cases be |
| 126considered a conditional sleep. 127.Pp 128See 129.Xr sx 9 130for details. 131.Ss Counting semaphores 132Counting semaphores provide a mechanism for synchronizing access 133to a pool of resources. --- 200 unchanged lines hidden (view full) --- 334for details. 335.Ss Context mode table 336The next table shows what can be used in different contexts. 337At this time this is a rather easy to remember table. 338.Bl -column ".Ic Xxxxxxxxxxxxxxxxxxx" ".Xr XXXXXXXXX" ".Xr XXXXXXX" ".Xr XXXXXXX" ".Xr XXXXXXX" ".Xr XXXXXX" -offset indent 339.It Xo 340.Em "Context:" Ta spin mtx Ta mutex Ta sx Ta rwlock Ta rmlock Ta sleep 341.Xc | 126considered a conditional sleep. 127.Pp 128See 129.Xr sx 9 130for details. 131.Ss Counting semaphores 132Counting semaphores provide a mechanism for synchronizing access 133to a pool of resources. --- 200 unchanged lines hidden (view full) --- 334for details. 335.Ss Context mode table 336The next table shows what can be used in different contexts. 337At this time this is a rather easy to remember table. 338.Bl -column ".Ic Xxxxxxxxxxxxxxxxxxx" ".Xr XXXXXXXXX" ".Xr XXXXXXX" ".Xr XXXXXXX" ".Xr XXXXXXX" ".Xr XXXXXX" -offset indent 339.It Xo 340.Em "Context:" Ta spin mtx Ta mutex Ta sx Ta rwlock Ta rmlock Ta sleep 341.Xc |
| 342.It interrupt filter: Ta \&ok Ta \&no Ta \&no Ta \&no Ta \&no Ta \&no 343.It interrupt thread: Ta \&ok Ta \&ok Ta \&no Ta \&ok Ta \&ok Ta \&no 344.It callout: Ta \&ok Ta \&ok Ta \&no Ta \&ok Ta \&no Ta \&no 345.It syscall: Ta \&ok Ta \&ok Ta \&ok Ta \&ok Ta \&ok Ta \&ok | 342.It interrupt filter: Ta \&ok Ta \&no Ta \&no Ta \&no Ta \&no Ta \&no 343.It interrupt thread: Ta \&ok Ta \&ok Ta \&no Ta \&ok Ta \&ok Ta \&no 344.It callout: Ta \&ok Ta \&ok Ta \&no Ta \&ok Ta \&no Ta \&no 345.It syscall: Ta \&ok Ta \&ok Ta \&ok Ta \&ok Ta \&ok Ta \&ok |
| 346.El 347.Sh SEE ALSO 348.Xr witness 4 , 349.Xr condvar 9 , 350.Xr lock 9 , 351.Xr mtx_pool 9 , 352.Xr mutex 9 , 353.Xr rmlock 9 , --- 14 unchanged lines hidden --- | 346.El 347.Sh SEE ALSO 348.Xr witness 4 , 349.Xr condvar 9 , 350.Xr lock 9 , 351.Xr mtx_pool 9 , 352.Xr mutex 9 , 353.Xr rmlock 9 , --- 14 unchanged lines hidden --- |