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[dragonfly.git] / lib / libpthread / pthread_rwlock_timedrdlock.3
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1.\" Copyright (c) 2004 Michael Telahun Makonnen
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25.\" $FreeBSD: src/share/man/man3/pthread_rwlock_timedrdlock.3,v 1.3 2007/10/22 10:08:00 ru Exp $
26.\"
27.Dd July 10, 2009
28.Dt PTHREAD_RWLOCK_TIMEDRDLOCK 3
29.Os
30.Sh NAME
31.Nm pthread_rwlock_timedrdlock
32.Nd "acquire a read-write lock for reading or give up after a specified period"
33.Sh LIBRARY
34.Lb libpthread
35.Sh SYNOPSIS
36.In pthread.h
37.Ft int
38.Fn pthread_rwlock_timedrdlock "pthread_rwlock_t *rwlock" "const struct timespec *abs_timeout"
39.Sh DESCRIPTION
40This function acquires a read lock on the read-write lock
41.Fa rwlock .
42However, if the lock cannot be
43acquired without waiting for another thread to
44unlock the lock,
45this wait shall be terminated when
46.Fa abs_timeout
47expires.
48.Pp
49A thread may hold multiple concurrent read locks.
50The
51.Xr pthread_rwlock_unlock 3
52function must be called once for each lock acquired.
53.Pp
54If the thread should be interrupted by a signal,
55the
56.Fn pthread_rwlock_timedrdlock
57function will be automatically restarted after the thread returns from
58the signal handler.
59.Pp
60The calling thread may deadlock if
61at the time the call is made it holds a write lock on
62.Fa rwlock .
63The results are undefined if this function is called with
64an uninitialized read-write lock.
65.Sh IMPLEMENTATION NOTES
66To prevent writer starvation, writers are favored over readers.
67.Sh RETURN VALUES
68If successful, the
69.Fn pthread_rwlock_timedrdlock
70function will return zero.
71Otherwise, an error number will be returned to indicate the error.
72.Pp
73This function shall not return an error code of
74.Er EINTR .
75.Sh ERRORS
76The
77.Fn pthread_rwlock_timedrdlock
78function will fail if:
79.Bl -tag -width Er
80.It Bq Er ETIMEDOUT
81The lock could not be acquired before the specified timeout expired.
82.El
83.Pp
84The
85.Fn pthread_rwlock_timedrdlock
86function may fail if:
87.Bl -tag -width Er
88.It Bq Er EAGAIN
89The read lock could not be
90acquired because the maximum number of read locks for
91.Fa rwlock
92would be exceeded.
93.It Bq Er EDEADLK
94The calling thread already holds a write lock on
95.Fa rwlock .
96.It Bq Er EINVAL
97The value specified by
98.Fa rwlock
99does not refer to an initialized read-write lock object,
100or the
101.Fa abs_timeout
102nanosecond value is less than zero or
103greater than or equal to 1 billion.
104.El
105.Sh SEE ALSO
106.Xr pthread_rwlock_init 3 ,
107.Xr pthread_rwlock_timedwrlock 3 ,
108.Xr pthread_rwlock_unlock 3
109.Sh STANDARDS
110The
111.Fn pthread_rwlock_timedrdlock
112function is expected to conform to
113.St -p1003.1-96 .
114.Sh HISTORY
115The
116.Fn pthread_rwlock_timedrdlock
117function first appeared in
118.Fx 5.2 .