1pthread_mutex_lock(3C) Standard C Library Functions pthread_mutex_lock(3C)
2
6 pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_unlock - lock
7 or unlock a mutex
8
10 cc -mt [ flag... ] file... -lpthread [ library... ]
11 #include <pthread.h>
12 int pthread_mutex_lock(pthread_mutex_t *mutex);
14 int pthread_mutex_trylock(pthread_mutex_t *mutex);
17 int pthread_mutex_unlock(pthread_mutex_t *mutex);
20
23 The mutex object referenced by mutex is locked by calling
24 pthread_mutex_lock(). If the mutex is already locked, the calling
25 thread blocks until the mutex becomes available. This operation returns
26 with the mutex object referenced by mutex in the locked state with the
27 calling thread as its owner.
28 If the mutex type is PTHREAD_MUTEX_NORMAL, deadlock detection is not
31 provided. Attempting to relock the mutex causes deadlock. If a thread
32 attempts to unlock a mutex that it has not locked or a mutex that is
33 unlocked, undefined behavior results.
34 If the mutex type is PTHREAD_MUTEX_ERRORCHECK, then error checking is
37 provided. If a thread attempts to relock a mutex that it has already
38 locked, an error will be returned. If a thread attempts to unlock a
39 mutex that it has not locked or a mutex which is unlocked, an error
40 will be returned.
41 If the mutex type is PTHREAD_MUTEX_RECURSIVE, then the mutex main‐
44 tains the concept of a lock count. When a thread successfully acquires
45 a mutex for the first time, the lock count is set to 1. Every time a
46 thread relocks this mutex, the lock count is incremented by one. Each
47 time the thread unlocks the mutex, the lock count is decremented by
48 one. When the lock count reaches 0, the mutex becomes available for
49 other threads to acquire. If a thread attempts to unlock a mutex that
50 it has not locked or a mutex that is unlocked, an error will be
51 returned.
52 If the mutex type is PTHREAD_MUTEX_DEFAULT, attempting to recursively
55 lock the mutex results in undefined behavior. Attempting to unlock the
56 mutex if it was not locked by the calling thread results in undefined
57 behavior. Attempting to unlock the mutex if it is not locked results in
58 undefined behavior.
59 The pthread_mutex_trylock() function is identical to
62 pthread_mutex_lock() except that if the mutex object referenced by
63 mutex is currently locked (by any thread, including the current
64 thread), the call fails immediately with EBUSY.
65 The pthread_mutex_unlock() function releases the mutex object refer‐
68 enced by mutex. The manner in which a mutex is released is dependent
69 upon the mutex's type attribute. If there are threads blocked on the
70 mutex object referenced by mutex when pthread_mutex_unlock() is called,
71 resulting in the mutex becoming available, the scheduling policy is
72 used to determine which thread will acquire the mutex. (In the case of
73 PTHREAD_MUTEX_RECURSIVE mutexes, the mutex becomes available when the
74 count reaches 0 and the calling thread no longer has any locks on this
75 mutex.)
76 If a signal is delivered to a thread waiting for a mutex, upon return
79 from the signal handler the thread resumes waiting for the mutex as if
80 it was not interrupted.
81
83 If successful, the pthread_mutex_lock() and pthread_mutex_unlock()
84 functions return 0. Otherwise, an error number is returned to indicate
85 the error.
86 The pthread_mutex_trylock() function returns 0 if a lock on the mutex
89 object referenced by mutex is acquired. Otherwise, an error number is
90 returned to indicate the error.
91
93 The pthread_mutex_lock() and pthread_mutex_trylock() functions will
94 fail if:
95 EAGAIN The mutex could not be acquired because the maximum number of
97 recursive locks for mutex has been exceeded.
98 EINVAL The mutex was created with the protocol attribute having the
101 value PTHREAD_PRIO_PROTECT and the calling thread's priority
102 is higher than the mutex's current priority ceiling.
103 EPERM The mutex was created with the protocol attribute having the
106 value PTHREAD_PRIO_PROTECT and the calling thread is not in
107 the real-time class (SCHED_RR or SCHED_FIFO scheduling
108 class).
109 The pthread_mutex_trylock() function will fail if:
113 EBUSY The mutex could not be acquired because it was already locked.
115 The pthread_mutex_lock(), pthread_mutex_trylock() and
119 pthread_mutex_unlock() functions may fail if:
120 EINVAL The value specified by mutex does not refer to an initialized
122 mutex object.
123 The pthread_mutex_lock() function may fail if:
127 EDEADLK The current thread already owns the mutex.
129 ENOMEM The limit on the number of simultaneously held mutexes has
132 been exceeded.
133 The pthread_mutex_unlock() function will fail if:
137 EPERM The mutex type is PTHREAD_MUTEX_ERRORCHECK or the mutex is a
139 robust mutex, and the current thread does not own the mutex.
140 When a thread makes a call to pthread_mutex_lock() or
144 pthread_mutex_trylock(), if the mutex is initialized with the robust‐
145 ness attribute having the value PTHREAD_MUTEX_ROBUST (see
146 pthread_mutexattr_getrobust(3C)), the call will return these error val‐
147 ues if:
148 EOWNERDEAD The last owner of this mutex died while holding the
150 mutex, or the process containing the owner of the
151 mutex unmapped the memory containing the mutex or
152 performed one of the exec(2) functions. This mutex
153 is now owned by the caller. The caller must now
154 attempt to make the state protected by the mutex
155 consistent. If it is able to clean up the state,
156 then it should call pthread_mutex_consistent() for
157 the mutex and unlock the mutex. Subsequent calls to
158 pthread_mutex_lock() and pthread_mutex_trylock()
159 will behave normally, as before. If the caller is
160 not able to clean up the state, pthread_mutex_con‐
161 sistent() should not be called for the mutex, but
162 the mutex should be unlocked. Subsequent calls to
163 pthread_mutex_lock() and pthread_mutex_trylock()
164 will fail to acquire the mutex with the error value
165 ENOTRECOVERABLE. If the owner who acquired the lock
166 with EOWNERDEAD dies, the next owner will acquire
167 the lock with EOWNERDEAD.
168 ENOTRECOVERABLE The mutex trying to be acquired was protecting the
171 state that has been left irrecoverable by the
172 mutex's last owner. The mutex has not been acquired.
173 This condition can occur when the lock was previ‐
174 ously acquired with EOWNERDEAD, and the owner was
175 not able to clean up the state and unlocked the
176 mutex without calling pthread_mutex_consistent().
177
180 See attributes(5) for descriptions of the following attributes:
181 ┌─────────────────────────────┬─────────────────────────────┐
186 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
187 ├─────────────────────────────┼─────────────────────────────┤
188 │Interface Stability │Committed │
189 ├─────────────────────────────┼─────────────────────────────┤
190 │MT-Level │MT-Safe │
191 ├─────────────────────────────┼─────────────────────────────┤
192 │Standard │See standards(5). │
193 └─────────────────────────────┴─────────────────────────────┘
194
196 pthread_mutex_consistent(3C), pthread_mutex_init(3C), pthread_mutex‐
197 attr_setprotocol(3C), pthread_mutexattr_setrobust(3C), pthread_mutex‐
198 attr_settype(3C), attributes(5), standards(5)
199
201 In the current implementation of threads, pthread_mutex_lock(),
202 pthread_mutex_unlock(), mutex_lock(), mutex_unlock(),
203 pthread_mutex_trylock(), and mutex_trylock() do not validate the mutex
204 type. Therefore, an uninitialized mutex or a mutex with an invalid
205 type does not return EINVAL. Interfaces for mutexes with an invalid
206 type have unspecified behavior.
207 Uninitialized mutexes that are allocated locally may contain junk data.
210 Such mutexes need to be initialized using pthread_mutex_init() or
211 mutex_init().
212SunOS 5.11 11 Nov 2008 pthread_mutex_lock(3C)