1.\" $OpenBSD: pthread_mutex_lock.3,v 1.11 2013/06/05 03:44:50 tedu Exp $
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3.\" Copyright (c) 1997 Brian Cully <shmit@kublai.com>
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30.\" $FreeBSD: pthread_mutex_lock.3,v 1.5 1999/08/28 00:03:07 peter Exp $
31.\"
32.Dd $Mdocdate: June 5 2013 $
33.Dt PTHREAD_MUTEX_LOCK 3
34.Os
35.Sh NAME
36.Nm pthread_mutex_lock ,
37.Nm pthread_mutex_timedlock ,
38.Nm pthread_mutex_trylock
39.Nd lock a mutex
40.Sh SYNOPSIS
41.In pthread.h
42.Ft int
43.Fn pthread_mutex_lock "pthread_mutex_t *mutex"
44.Ft int
45.Fn pthread_mutex_timedlock "pthread_mutex_t *mutex" "const struct timespec *abstime"
46.Ft int
47.Fn pthread_mutex_trylock "pthread_mutex_t *mutex"
48.Sh DESCRIPTION
49The
50.Fn pthread_mutex_lock
51function locks
52.Fa mutex .
53If the mutex is currently locked by another thread,
54the calling thread will block until the
55mutex becomes available.
56.Pp
57If the mutex is currently locked by the calling thread,
58then the behavior depends on the type of the mutex.
59If
60.Fa mutex
61is of type
62.Dv PTHREAD_MUTEX_NORMAL ,
63then the calling thread will deadlock and never return from
64.Fn pthread_mutex_lock .
65If
66.Fa mutex
67is of type
68.Dv PTHREAD_MUTEX_ERRORCHECK ,
69then
70.Er EDEADLK
71is immediately returned.
72If
73.Fa mutex
74is of type
75.Dv PTHREAD_MUTEX_RECURSIVE ,
76then the recursion count on the mutex is incremented.
77.Pp
78The
79.Fn pthread_mutex_timedlock
80function locks
81.Fa mutex
82like
83.Fn pthread_mutex_lock
84except that it will not block or deadlock past the system time
85specified in
86.Fa abstime .
87If that time is reached without being able to lock
88.Fa mutex ,
89then it returns
90.Er ETIMEDOUT .
91.Pp
92The
93.Fn pthread_mutex_trylock
94function locks
95.Fa mutex
96like
97.Fn pthread_mutex_lock
98except that if
99.Fa mutex
100is locked by another thread,
101or is locked by the calling thread and is not of type
102.Dv PTHREAD_MUTEX_RECURSIVE ,
103then it will immediately return
104.Er EBUSY .
105.Sh RETURN VALUES
106If successful,
107.Fn pthread_mutex_lock ,
108.Fn pthread_mutex_timedlock ,
109and
110.Fn pthread_mutex_trylock
111will return zero, otherwise an error number will be returned to
112indicate the error.
113.Sh ERRORS
114.Fn pthread_mutex_lock ,
115.Fn pthread_mutex_timedlock ,
116and
117.Fn pthread_mutex_trylock
118will fail if:
119.Bl -tag -width Er
120.It Bq Er EINVAL
121The value specified by
122.Fa mutex
123is invalid.
124.It Bq Er EAGAIN
125The mutex is of type
126.Dv PTHREAD_MUTEX_RECURSIVE
127and the maximum recursion count has been reached.
128.El
129.Pp
130In addition,
131.Fn pthread_mutex_lock
132and
133.Fn pthread_mutex_timedlock
134may return the following error:
135.Bl -tag -width Er
136.It Bq Er EDEADLK
137The mutex is of type
138.Dv PTHREAD_MUTEX_ERRORCHECK
139and is already locked by the calling thread.
140.El
141.Pp
142.Fn pthread_mutex_timedlock
143may return the following error:
144.Bl -tag -width Er
145.It Bq Er ETIMEDOUT
146The mutex could not be locked and the specified time was reached.
147.El
148.Pp
149.Fn pthread_mutex_trylock
150may return the following error:
151.Bl -tag -width Er
152.It Bq Er EBUSY
153The mutex could not be locked because it was already locked.
154.El
155.Sh SEE ALSO
156.Xr pthread_mutex_destroy 3 ,
157.Xr pthread_mutex_init 3 ,
158.Xr pthread_mutex_unlock 3 ,
159.Xr pthread_mutexattr_settype 3
160.Sh STANDARDS
161.Fn pthread_mutex_lock ,
162.Fn pthread_mutex_timedlock ,
163and
164.Fn pthread_mutex_trylock
165conform to
166.St -p1003.1-2008 .
167