/share/man/man3/pthread_rwlock_rdlock.3
https://bitbucket.org/freebsd/freebsd-head/ · Unknown · 127 lines · 127 code · 0 blank · 0 comment · 0 complexity · 5a49796bd08d7b754b62a52c56e1fdfd MD5 · raw file
- .\" Copyright (c) 1998 Alex Nash
- .\" All rights reserved.
- .\"
- .\" Redistribution and use in source and binary forms, with or without
- .\" modification, are permitted provided that the following conditions
- .\" are met:
- .\" 1. Redistributions of source code must retain the above copyright
- .\" notice, this list of conditions and the following disclaimer.
- .\" 2. Redistributions in binary form must reproduce the above copyright
- .\" notice, this list of conditions and the following disclaimer in the
- .\" documentation and/or other materials provided with the distribution.
- .\"
- .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
- .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- .\" SUCH DAMAGE.
- .\"
- .\" $FreeBSD$
- .\"
- .Dd August 4, 1998
- .Dt PTHREAD_RWLOCK_RDLOCK 3
- .Os
- .Sh NAME
- .Nm pthread_rwlock_rdlock ,
- .Nm pthread_rwlock_tryrdlock
- .Nd acquire a read/write lock for reading
- .Sh LIBRARY
- .Lb libpthread
- .Sh SYNOPSIS
- .In pthread.h
- .Ft int
- .Fn pthread_rwlock_rdlock "pthread_rwlock_t *lock"
- .Ft int
- .Fn pthread_rwlock_tryrdlock "pthread_rwlock_t *lock"
- .Sh DESCRIPTION
- The
- .Fn pthread_rwlock_rdlock
- function acquires a read lock on
- .Fa lock
- provided that
- .Fa lock
- is not presently held for writing and no writer threads are
- presently blocked on the lock.
- If the read lock cannot be
- immediately acquired, the calling thread blocks until it can
- acquire the lock.
- .Pp
- The
- .Fn pthread_rwlock_tryrdlock
- function performs the same action, but does not block if the lock
- cannot be immediately obtained (i.e., the lock is held for writing
- or there are waiting writers).
- .Pp
- A thread may hold multiple concurrent read locks.
- If so,
- .Fn pthread_rwlock_unlock
- must be called once for each lock obtained.
- .Pp
- The results of acquiring a read lock while the calling thread holds
- a write lock are undefined.
- .Sh IMPLEMENTATION NOTES
- To prevent writer starvation, writers are favored over readers.
- .Sh RETURN VALUES
- If successful, the
- .Fn pthread_rwlock_rdlock
- and
- .Fn pthread_rwlock_tryrdlock
- functions will return zero.
- Otherwise an error number will be returned
- to indicate the error.
- .Sh ERRORS
- The
- .Fn pthread_rwlock_tryrdlock
- function will fail if:
- .Bl -tag -width Er
- .It Bq Er EBUSY
- The lock could not be acquired because a writer holds the lock or
- was blocked on it.
- .El
- .Pp
- The
- .Fn pthread_rwlock_rdlock
- and
- .Fn pthread_rwlock_tryrdlock
- functions may fail if:
- .Bl -tag -width Er
- .It Bq Er EAGAIN
- The lock could not be acquired because the maximum number of read locks
- against
- .Fa lock
- has been exceeded.
- .It Bq Er EDEADLK
- The current thread already owns
- .Fa lock
- for writing.
- .It Bq Er EINVAL
- The value specified by
- .Fa lock
- is invalid.
- .It Bq Er ENOMEM
- Insufficient memory exists to initialize the lock (applies to
- statically initialized locks only).
- .El
- .Sh SEE ALSO
- .Xr pthread_rwlock_init 3 ,
- .Xr pthread_rwlock_trywrlock 3 ,
- .Xr pthread_rwlock_unlock 3 ,
- .Xr pthread_rwlock_wrlock 3
- .Sh STANDARDS
- The
- .Fn pthread_rwlock_rdlock
- and
- .Fn pthread_rwlock_tryrdlock
- functions are expected to conform to
- .St -susv2 .
- .Sh HISTORY
- The
- .Fn pthread_rwlock_rdlock
- function first appeared in
- .Fx 3.0 .