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48.Dd February 17, 2023
49.Dt PTHREAD_MUTEX_INIT 3C
50.Os
51.Sh NAME
52.Nm pthread_mutex_init ,
53.Nm pthread_mutex_destroy
54.Nd initialize or destroy a mutex
55.Sh SYNOPSIS
56.In pthread.h
57.Ft int
58.Fo pthread_mutex_init
59.Fa "pthread_mutex_t *restrict mutex"
60.Fa "const pthread_mutexattr_t *restrict attr"
61.Fc
62.Ft int
63.Fo pthread_mutex_destroy
64.Fa "pthread_mutex_t *mutex"
65.Fc
66.Vt pthread_mutex_t
67.Va mutex
68.No =
69.Dv PTHREAD_MUTEX_INITIALIZER ;
70.Vt pthread_mutex_t
71.Va ecmutex
72.No =
73.Dv PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP ;
74.Vt pthread_mutex_t
75.Va rmutex
76.No =
77.Dv PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP ;
78.Sh DESCRIPTION
79The
80.Fn pthread_mutex_init
81function initializes the mutex referenced by
82.Fa mutex
83with attributes specified by
84.Fa attr .
85If
86.Fa attr
87is
88.Dv NULL ,
89the default mutex attributes are used; the effect is the same as
90passing the address of a default mutex attributes object.
91Upon successful
92initialization, the state of the mutex becomes initialized and unlocked.
93.Pp
94Except for robust mutexes, attempting to initialize an already initialized
95mutex results in undefined behavior.
96.Pp
97The
98.Fn pthread_mutex_destroy
99function destroys the mutex object referenced by
100.Fa mutex ;
101the mutex object becomes, in effect, uninitialized.
102A destroyed mutex object can be re-initialized using
103.Fn pthread_mutex_init ;
104the results of otherwise referencing the object after it has been destroyed are
105undefined.
106.Pp
107It is safe to destroy an initialized mutex that is unlocked.
108Attempting to destroy a locked mutex results in undefined behavior.
109.Pp
110In cases where default mutex attributes are appropriate, the macro
111.Dv PTHREAD_MUTEX_INITIALIZER
112can be used to initialize mutexes that are statically allocated.
113The effect is equivalent to dynamic initialization by a call to
114.Fn pthread_mutex_init
115with parameter
116.Fa attr
117specified as
118.Dv NULL .
119.Pp
120In cases where error checking mutex attributes are appropriate, the macro
121.Dv PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
122can be used to initialize mutexes that are statically allocated.
123The effect is equivalent to dynamic initialization by a call to
124.Fn pthread_mutex_init
125with parameter
126.Fa attr
127initialized with
128.Xr pthread_mutexattr_init 3C
129and its type set to
130.Dv PTHREAD_MUTEX_ERRORCHECK .
131.Pp
132In cases where recursive mutex attributes are appropriate, the macro
133.Dv PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
134can be used to initialize mutexes that are statically allocated.
135The effect is equivalent to dynamic initialization by a call to
136.Fn pthread_mutex_init
137with parameter
138.Fa attr
139initialized with
140.Xr pthread_mutexattr_init 3C
141and its type set to
142.Dv PTHREAD_MUTEX_RECURSIVE .
143.Sh RETURN VALUES
144If successful, the
145.Fn pthread_mutex_init
146and
147.Fn pthread_mutex_destroy
148functions return
149.Sy 0 .
150Otherwise, an error number is returned to indicate the error.
151.Sh ERRORS
152The
153.Fn pthread_mutex_init
154function will fail if:
155.Bl -tag -width Er
156.It Er EAGAIN
157The system lacked the necessary resources
158.Pq other than memory
159to initialize another mutex.
160.It Er EBUSY
161An attempt was detected to re-initialize a robust mutex previously initialized
162but not yet destroyed.
163See
164.Xr pthread_mutexattr_setrobust 3C .
165.It Ev EINVAL
166An attempt was detected to re-initialize a robust mutex previously initialized
167with a different set of attributes.
168See
169.Xr pthread_mutexattr_setrobust 3C .
170.It Er ENOMEM
171Insufficient memory exists to initialize the mutex.
172.It Er EPERM
173The caller does not have the privilege to perform the operation.
174.El
175.Pp
176The
177.Fn pthread_mutex_init
178function may fail if:
179.Bl -tag -width Er
180.It Er EBUSY
181An attempt was detected to re-initialize the object referenced by
182.Fa mutex ,
183a mutex previously initialized but not yet destroyed.
184.It Er EINVAL
185The value specified by
186.Fa attr
187or
188.Fa mutex
189is invalid.
190.El
191.Pp
192The
193.Fn pthread_mutex_destroy
194function may fail if:
195.Bl -tag -width Er
196.It Er EBUSY
197An attempt was detected to destroy the object referenced by
198.Fa mutex
199while it is locked or referenced
200.Po
201for example, while being used in a
202.Xr pthread_cond_wait 3C
203or
204.Xr pthread_cond_timedwait 3C
205.Pc
206by another thread.
207.It Er EINVAL
208The value specified by
209.Fa mutex
210is invalid.
211.El
212.Sh INTERFACE STABILITY
213.Sy Committed
214.Sh MT-LEVEL
215.Sy MT-Safe
216.Sh SEE ALSO
217.Xr pthread_cond_timedwait 3C ,
218.Xr pthread_cond_wait 3C ,
219.Xr pthread_mutex_lock 3C ,
220.Xr pthread_mutexattr_init 3C ,
221.Xr pthread_mutexattr_setrobust 3C ,
222.Xr pthread_mutexattr_settype 3C ,
223.Xr attributes 7 ,
224.Xr mutex 7
225