diff options
Diffstat (limited to 'share/man/man9/mtx_pool.9')
| -rw-r--r-- | share/man/man9/mtx_pool.9 | 184 |
1 files changed, 184 insertions, 0 deletions
diff --git a/share/man/man9/mtx_pool.9 b/share/man/man9/mtx_pool.9 new file mode 100644 index 0000000..ab2cc8b --- /dev/null +++ b/share/man/man9/mtx_pool.9 @@ -0,0 +1,184 @@ +.\" +.\" Copyright (C) 2002 Garrett Rooney <rooneg@electricjellyfish.net>. +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice(s), this list of conditions and the following disclaimer as +.\" the first lines of this file unmodified other than the possible +.\" addition of one or more copyright notices. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice(s), this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY +.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED +.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE +.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY +.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES +.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR +.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH +.\" DAMAGE. +.\" +.\" $FreeBSD$ +.\" +.Dd February 6, 2010 +.Dt MTX_POOL 9 +.Os +.Sh NAME +.Nm mtx_pool , +.Nm mtx_pool_alloc , +.Nm mtx_pool_find , +.Nm mtx_pool_lock , +.Nm mtx_pool_lock_spin , +.Nm mtx_pool_unlock , +.Nm mtx_pool_unlock_spin , +.Nm mtx_pool_create , +.Nm mtx_pool_destroy +.Nd "mutex pool routines" +.Sh SYNOPSIS +.In sys/param.h +.In sys/lock.h +.In sys/mutex.h +.Ft "struct mtx *" +.Fn mtx_pool_alloc "struct mtx_pool *pool" +.Ft "struct mtx *" +.Fn mtx_pool_find "struct mtx_pool *pool" "void *ptr" +.Ft void +.Fn mtx_pool_lock "struct mtx_pool *pool" "void *ptr" +.Ft void +.Fn mtx_pool_lock_spin "struct mtx_pool *pool" "void *ptr" +.Ft void +.Fn mtx_pool_unlock "struct mtx_pool *pool" "void *ptr" +.Ft void +.Fn mtx_pool_unlock_spin "struct mtx_pool *pool" "void *ptr" +.Ft "struct mtx_pool *" +.Fn mtx_pool_create "const char *mtx_name" "int pool_size" "int opts" +.Ft "void" +.Fn mtx_pool_destroy "struct mtx_pool **poolp" +.Sh DESCRIPTION +Mutex pools are designed to be used as short term leaf mutexes; +i.e., the last mutex one might acquire before calling +.Xr mtx_sleep 9 . +They operate using a shared pool of mutexes. +A mutex may be chosen from the pool based on a supplied pointer, +which may or may not point to anything valid, +or the caller may allocate an arbitrary shared mutex from the pool +and save the returned mutex pointer for later use. +.Pp +The shared mutexes in the +.Va mtxpool_sleep +mutex pool, +which is created by default, +are standard, non-recursive, +blockable mutexes, and should only be used in appropriate situations. +The mutexes in the +.Va mtxpool_lockbuilder +mutex pool are similar, except that they are initialized with the MTX_NOWITNESS +flag so that they may be used to build higher-level locks. +Other mutex pools may be created that contain mutexes with different +properties, such as spin mutexes. +.Pp +The caller can lock and unlock mutexes returned by the pool routines, but +since the mutexes are shared, the caller should not attempt to destroy them +or modify their characteristics. +While pool mutexes are normally leaf mutexes +(meaning that one cannot depend on any ordering guarantees +after obtaining one), +one can still obtain other mutexes under carefully controlled circumstances. +Specifically, if one has a private mutex +(one that was allocated and initialized by the caller), +one can obtain it after obtaining a pool mutex if ordering issues are +carefully accounted for. +In these cases the private mutex winds up being the true leaf mutex. +.Pp +Pool mutexes have the following advantages: +.Pp +.Bl -enum -offset indent -compact +.It +No structural overhead; +i.e., they can be associated with a structure without adding bloat to it. +.It +Mutexes can be obtained for invalid pointers, which is useful when one uses +mutexes to interlock destructor operations. +.It +No initialization or destruction overhead. +.It +Can be used with +.Xr mtx_sleep 9 . +.El +.Pp +And the following disadvantages: +.Pp +.Bl -enum -offset indent -compact +.It +Should generally only be used as leaf mutexes. +.It +Pool/pool dependency ordering cannot be guaranteed. +.It +Possible L1 cache mastership contention between CPUs. +.El +.Pp +.Fn mtx_pool_alloc +obtains a shared mutex from the specified pool. +This routine uses a simple rover to choose one of the shared mutexes managed +by the +.Nm +subsystem. +.Pp +.Fn mtx_pool_find +returns the shared mutex associated with the specified address. +This routine will create a hash out of the pointer passed into it +and will choose a shared mutex from the specified pool based on that hash. +The pointer does not need to point to anything real. +.Pp +.Fn mtx_pool_lock , +.Fn mtx_pool_lock_spin , +.Fn mtx_pool_unlock , +and +.Fn mtx_pool_unlock_spin +lock and unlock the shared mutex from the specified pool +associated with the specified address; +they are a combination of +.Fn mtx_pool_find +and +.Xr mtx_lock 9 , +.Xr mtx_lock_spin 9 , +.Xr mtx_unlock 9 , +and +.Xr mtx_unlock_spin 9 , +respectively. +Since these routines must first find the mutex to operate on, +they are not as fast as directly using the mutex pointer returned by +a previous invocation of +.Fn mtx_pool_find +or +.Fn mtx_pool_alloc . +.Pp +.Fn mtx_pool_create +allocates and initializes a new mutex pool of the +specified size. +The pool size must be a power of two. +The +.Fa opts +argument is passed to +.Xr mtx_init 9 +to set the options for each mutex in the pool. +.Pp +.Fn mtx_pool_destroy +calls +.Xr mtx_destroy 9 +on each mutex in the specified pool, +deallocates the memory associated with the pool, +and assigns NULL to the pool pointer. +.Sh SEE ALSO +.Xr locking 9 , +.Xr mutex 9 +.Sh HISTORY +These routines first appeared in +.Fx 5.0 . |
