/share/man/man3/pthread_rwlock_timedrdlock.3

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 25.\" $FreeBSD$
 26.\"
 27.Dd January 16, 2004
 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 .