1.\" $OpenBSD: mutex.9,v 1.7 2007/12/09 20:54:01 jmc Exp $ 2.\" 3.\" Copyright (c) 2005 Pedro Martelletto <pedro@ambientworks.net> 4.\" All rights reserved. 5.\" 6.\" Permission to use, copy, modify, and distribute this software for any 7.\" purpose with or without fee is hereby granted, provided that the above 8.\" copyright notice and this permission notice appear in all copies. 9.\" 10.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 11.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 12.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 13.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 14.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 15.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 16.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 17.\" 18.Dd $Mdocdate: December 9 2007 $ 19.Dt MUTEX 9 20.Os 21.Sh NAME 22.Nm mutex , 23.Nm mtx_init , 24.Nm mtx_enter , 25.Nm mtx_leave 26.Nd interface to CPU mutexes 27.Sh SYNOPSIS 28.Fd #include <sys/mutex.h> 29.Ft void 30.Fn mtx_init "struct mutex *mtxp" "int wantipl" 31.Ft void 32.Fn mtx_enter "struct mutex *mtxp" 33.Ft void 34.Fn mtx_leave "struct mutex *mtxp" 35.Sh DESCRIPTION 36The 37.Nm 38set of functions provides a non-recursive, interrupt-aware spinning mechanism 39to ensure mutual exclusion between different CPUs. 40.Pp 41The 42.Fn mtx_init 43function is used to initiate the mutex pointed to by 44.Fa mtxp . 45When acquired, the mutex will cause the processor interrupt level to be raised 46to 47.Fa wantipl 48if necessary. 49.Pp 50The 51.Fn mtx_enter 52function acquires a mutex, spinning if necessary. 53.Pp 54The 55.Fn mtx_leave 56function releases a mutex. 57In case the acquisition of the mutex caused the interrupt level to be changed, 58it is then restored. 59.Sh SEE ALSO 60.Xr lockmgr 9 , 61.Xr rwlock 9 , 62.Xr spl 9 63.Sh HISTORY 64The 65.Nm 66functions first appeared in 67.Ox 3.6 . 68.Sh AUTHORS 69The 70.Nm 71functions were written by 72.An Artur Grabowski 73.Aq art@openbsd.org . 74.Sh CAVEATS 75As these are spinning locks, don't sleep while holding one. 76.Pp 77If using a mutex in an interrupt handler, locks must be initialised 78with the correct IPL or deadlock will occur. 79.Pp 80Multiple mutexes may be nested, but not interleaved. 81This is okay: 82.Bd -literal -offset indent 83mtx_enter(foo); 84mtx_enter(bar); 85mtx_leave(bar); 86mtx_leave(foo); 87.Ed 88.Pp 89While this is 90.Fa not : 91.Bd -literal -offset indent 92mtx_enter(foo); 93mtx_enter(bar); 94mtx_leave(foo); 95mtx_leave(bar); 96.Ed 97