.\" .\" Sun Microsystems, Inc. gratefully acknowledges The Open Group for .\" permission to reproduce portions of its copyrighted documentation. .\" Original documentation from The Open Group can be obtained online at .\" http://www.opengroup.org/bookstore/. .\" .\" The Institute of Electrical and Electronics Engineers and The Open .\" Group, have given us permission to reprint portions of their .\" documentation. .\" .\" In the following statement, the phrase ``this text'' refers to portions .\" of the system documentation. .\" .\" Portions of this text are reprinted and reproduced in electronic form .\" in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition, .\" Standard for Information Technology -- Portable Operating System .\" Interface (POSIX), The Open Group Base Specifications Issue 6, .\" Copyright (C) 2001-2004 by the Institute of Electrical and Electronics .\" Engineers, Inc and The Open Group. In the event of any discrepancy .\" between these versions and the original IEEE and The Open Group .\" Standard, the original IEEE and The Open Group Standard is the referee .\" document. The original Standard can be obtained online at .\" http://www.opengroup.org/unix/online.html. .\" .\" This notice shall appear on any product containing this material. .\" .\" The contents of this file are subject to the terms of the .\" Common Development and Distribution License (the "License"). .\" You may not use this file except in compliance with the License. .\" .\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE .\" or http://www.opensolaris.org/os/licensing. .\" See the License for the specific language governing permissions .\" and limitations under the License. .\" .\" When distributing Covered Code, include this CDDL HEADER in each .\" file and include the License file at usr/src/OPENSOLARIS.LICENSE. .\" If applicable, add the following below this CDDL HEADER, with the .\" fields enclosed by brackets "[]" replaced with your own identifying .\" information: Portions Copyright [yyyy] [name of copyright owner] .\" .\" .\" Copyright 1991, 1992, 1994, The X/Open Company Ltd. .\" Copyright (c) 2001, The IEEE and The Open Group. All Rights Reserved. .\" Copyright (c) 2008, Sun Microsystems, Inc. All Rights Reserved. .\" .TH PTHREAD_MUTEX_LOCK 3C "Nov 11, 2008" .SH NAME pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_unlock \- lock or unlock a mutex .SH SYNOPSIS .LP .nf cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ] #include \fBint\fR \fBpthread_mutex_lock\fR(\fBpthread_mutex_t *\fR\fImutex\fR); .fi .LP .nf \fBint\fR \fBpthread_mutex_trylock\fR(\fBpthread_mutex_t *\fR\fImutex\fR); .fi .LP .nf \fBint\fR \fBpthread_mutex_unlock\fR(\fBpthread_mutex_t *\fR\fImutex\fR); .fi .SH DESCRIPTION .sp .LP The mutex object referenced by mutex is locked by calling \fBpthread_mutex_lock()\fR. If the mutex is already locked, the calling thread blocks until the mutex becomes available. This operation returns with the mutex object referenced by mutex in the locked state with the calling thread as its owner. .sp .LP If the mutex type is \fBPTHREAD_MUTEX_NORMAL\fR, deadlock detection is not provided. Attempting to relock the mutex causes deadlock. If a thread attempts to unlock a mutex that it has not locked or a mutex that is unlocked, undefined behavior results. .sp .LP If the mutex type is \fBPTHREAD_MUTEX_ERRORCHECK\fR, then error checking is provided. If a thread attempts to relock a mutex that it has already locked, an error will be returned. If a thread attempts to unlock a mutex that it has not locked or a mutex which is unlocked, an error will be returned. .sp .LP If the mutex type is \fBPTHREAD_MUTEX_RECURSIVE\fR, then the mutex maintains the concept of a lock count. When a thread successfully acquires a mutex for the first time, the lock count is set to 1. Every time a thread relocks this mutex, the lock count is incremented by one. Each time the thread unlocks the mutex, the lock count is decremented by one. When the lock count reaches \fB0\fR, the mutex becomes available for other threads to acquire. If a thread attempts to unlock a mutex that it has not locked or a mutex that is unlocked, an error will be returned. .sp .LP If the mutex type is \fBPTHREAD_MUTEX_DEFAULT\fR, attempting to recursively lock the mutex results in undefined behavior. Attempting to unlock the mutex if it was not locked by the calling thread results in undefined behavior. Attempting to unlock the mutex if it is not locked results in undefined behavior. .sp .LP The \fBpthread_mutex_trylock()\fR function is identical to \fBpthread_mutex_lock()\fR except that if the mutex object referenced by \fImutex\fR is currently locked (by any thread, including the current thread), the call fails immediately with \fBEBUSY\fR. .sp .LP The \fBpthread_mutex_unlock()\fR function releases the mutex object referenced by \fImutex\fR. The manner in which a mutex is released is dependent upon the mutex's type attribute. If there are threads blocked on the mutex object referenced by \fImutex\fR when \fBpthread_mutex_unlock()\fR is called, resulting in the mutex becoming available, the scheduling policy is used to determine which thread will acquire the mutex. (In the case of \fBPTHREAD_MUTEX_RECURSIVE\fR mutexes, the mutex becomes available when the count reaches \fB0\fR and the calling thread no longer has any locks on this mutex.) .sp .LP If a signal is delivered to a thread waiting for a mutex, upon return from the signal handler the thread resumes waiting for the mutex as if it was not interrupted. .SH RETURN VALUES .sp .LP If successful, the \fBpthread_mutex_lock()\fR and \fBpthread_mutex_unlock()\fR functions return \fB0\fR. Otherwise, an error number is returned to indicate the error. .sp .LP The \fBpthread_mutex_trylock()\fR function returns \fB0\fR if a lock on the mutex object referenced by \fImutex\fR is acquired. Otherwise, an error number is returned to indicate the error. .SH ERRORS .sp .LP The \fBpthread_mutex_lock()\fR and \fBpthread_mutex_trylock()\fR functions will fail if: .sp .ne 2 .na \fB\fBEAGAIN\fR\fR .ad .RS 10n The mutex could not be acquired because the maximum number of recursive locks for mutex has been exceeded. .RE .sp .ne 2 .na \fB\fBEINVAL\fR\fR .ad .RS 10n The \fImutex\fR was created with the protocol attribute having the value \fBPTHREAD_PRIO_PROTECT\fR and the calling thread's priority is higher than the mutex's current priority ceiling. .RE .sp .ne 2 .na \fB\fBEPERM\fR\fR .ad .RS 10n The mutex was created with the protocol attribute having the value \fBPTHREAD_PRIO_PROTECT\fR and the calling thread is not in the real-time class (\fBSCHED_RR\fR or \fBSCHED_FIFO\fR scheduling class). .RE .sp .LP The \fBpthread_mutex_trylock()\fR function will fail if: .sp .ne 2 .na \fB\fBEBUSY\fR\fR .ad .RS 9n The \fImutex\fR could not be acquired because it was already locked. .RE .sp .LP The \fBpthread_mutex_lock()\fR, \fBpthread_mutex_trylock()\fR and \fBpthread_mutex_unlock()\fR functions may fail if: .sp .ne 2 .na \fB\fBEINVAL\fR\fR .ad .RS 10n The value specified by \fImutex\fR does not refer to an initialized mutex object. .RE .sp .LP The \fBpthread_mutex_lock()\fR function may fail if: .sp .ne 2 .na \fB\fBEDEADLK\fR\fR .ad .RS 11n The current thread already owns the mutex. .RE .sp .ne 2 .na \fB\fBENOMEM\fR\fR .ad .RS 11n The limit on the number of simultaneously held mutexes has been exceeded. .RE .sp .LP The \fBpthread_mutex_unlock()\fR function will fail if: .sp .ne 2 .na \fB\fBEPERM\fR\fR .ad .RS 9n The mutex type is PTHREAD_MUTEX_ERRORCHECK or the mutex is a robust mutex, and the current thread does not own the mutex. .RE .sp .LP When a thread makes a call to \fBpthread_mutex_lock()\fR or \fBpthread_mutex_trylock()\fR, if the mutex is initialized with the robustness attribute having the value \fBPTHREAD_MUTEX_ROBUST\fR (see \fBpthread_mutexattr_getrobust\fR(3C)), the call will return these error values if: .sp .ne 2 .na \fB\fBEOWNERDEAD\fR\fR .ad .RS 19n The last owner of this mutex died while holding the mutex, or the process containing the owner of the mutex unmapped the memory containing the mutex or performed one of the \fBexec\fR(2) functions. This mutex is now owned by the caller. The caller must now attempt to make the state protected by the mutex consistent. If it is able to clean up the state, then it should call \fBpthread_mutex_consistent()\fR for the mutex and unlock the mutex. Subsequent calls to \fBpthread_mutex_lock()\fR and \fBpthread_mutex_trylock()\fR will behave normally, as before. If the caller is not able to clean up the state, \fBpthread_mutex_consistent()\fR should not be called for the mutex, but the mutex should be unlocked. Subsequent calls to \fBpthread_mutex_lock()\fR and \fBpthread_mutex_trylock()\fR will fail to acquire the mutex with the error value \fBENOTRECOVERABLE\fR. If the owner who acquired the lock with \fBEOWNERDEAD\fR dies, the next owner will acquire the lock with \fBEOWNERDEAD\fR. .RE .sp .ne 2 .na \fB\fBENOTRECOVERABLE\fR\fR .ad .RS 19n The mutex trying to be acquired was protecting the state that has been left irrecoverable by the mutex's last owner. The mutex has not been acquired. This condition can occur when the lock was previously acquired with \fBEOWNERDEAD\fR, and the owner was not able to clean up the state and unlocked the mutex without calling \fBpthread_mutex_consistent()\fR. .RE .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Committed _ MT-Level MT-Safe _ Standard See \fBstandards\fR(5). .TE .SH SEE ALSO .sp .LP \fBpthread_mutex_consistent\fR(3C), \fBpthread_mutex_init\fR(3C), \fBpthread_mutexattr_setprotocol\fR(3C), \fBpthread_mutexattr_setrobust\fR(3C), \fBpthread_mutexattr_settype\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5) .SH NOTES .sp .LP In the current implementation of threads, \fBpthread_mutex_lock()\fR, \fBpthread_mutex_unlock()\fR, \fBmutex_lock()\fR, \fBmutex_unlock()\fR, \fBpthread_mutex_trylock()\fR, and \fBmutex_trylock()\fR do not validate the mutex type. Therefore, an uninitialized mutex or a mutex with an invalid type does not return \fBEINVAL\fR. Interfaces for mutexes with an invalid type have unspecified behavior. .sp .LP Uninitialized mutexes that are allocated locally may contain junk data. Such mutexes need to be initialized using \fBpthread_mutex_init()\fR or \fBmutex_init()\fR.