2a339d9e3d
intention of the POSIX IEEE Std 1003.1TM-2008/Cor 1-2013. A robust mutex is guaranteed to be cleared by the system upon either thread or process owner termination while the mutex is held. The next mutex locker is then notified about inconsistent mutex state and can execute (or abandon) corrective actions. The patch mostly consists of small changes here and there, adding neccessary checks for the inconsistent and abandoned conditions into existing paths. Additionally, the thread exit handler was extended to iterate over the userspace-maintained list of owned robust mutexes, unlocking and marking as terminated each of them. The list of owned robust mutexes cannot be maintained atomically synchronous with the mutex lock state (it is possible in kernel, but is too expensive). Instead, for the duration of lock or unlock operation, the current mutex is remembered in a special slot that is also checked by the kernel at thread termination. Kernel must be aware about the per-thread location of the heads of robust mutex lists and the current active mutex slot. When a thread touches a robust mutex for the first time, a new umtx op syscall is issued which informs about location of lists heads. The umtx sleep queues for PP and PI mutexes are split between non-robust and robust. Somewhat unrelated changes in the patch: 1. Style. 2. The fix for proper tdfind() call use in umtxq_sleep_pi() for shared pi mutexes. 3. Removal of the userspace struct pthread_mutex m_owner field. 4. The sysctl kern.ipc.umtx_vnode_persistent is added, which controls the lifetime of the shared mutex associated with a vnode' page. Reviewed by: jilles (previous version, supposedly the objection was fixed) Discussed with: brooks, Martin Simmons <martin@lispworks.com> (some aspects) Tested by: pho Sponsored by: The FreeBSD Foundation
90 lines
2.9 KiB
Groff
90 lines
2.9 KiB
Groff
.\" Copyright (c) 1997 Brian Cully <shmit@kublai.com>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the author nor the names of any co-contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 29, 2016
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.Dt PTHREAD_MUTEX_TRYLOCK 3
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.Os
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.Sh NAME
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.Nm pthread_mutex_trylock
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.Nd attempt to lock a mutex without blocking
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.Sh LIBRARY
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.Lb libpthread
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.Sh SYNOPSIS
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.In pthread.h
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.Ft int
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.Fn pthread_mutex_trylock "pthread_mutex_t *mutex"
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.Sh DESCRIPTION
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The
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.Fn pthread_mutex_trylock
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function locks
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.Fa mutex .
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If the mutex is already locked,
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.Fn pthread_mutex_trylock
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will not block waiting for the mutex, but will return an error condition.
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.Sh RETURN VALUES
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If successful,
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.Fn pthread_mutex_trylock
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will return zero, otherwise an error number will be returned to
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indicate the error.
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.Sh ERRORS
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The
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.Fn pthread_mutex_trylock
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function will fail if:
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.Bl -tag -width "Er ENOTRECOVERABLE"
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.It Bq Er EINVAL
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The value specified by
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.Fa mutex
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is invalid.
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.It Bq Er EBUSY
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.Fa Mutex
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is already locked.
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.It Bq Er EOWNERDEAD
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The argument
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.Fa mutex
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points to a robust mutex and the previous owning thread terminated
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while holding the mutex lock.
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The lock was granted to the caller and it is up to the new owner
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to make the state consistent.
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.It Bq Er ENOTRECOVERABLE
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The state protected by the
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.Fa mutex
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is not recoverable.
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.El
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.Sh SEE ALSO
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.Xr pthread_mutex_consistent 3 ,
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.Xr pthread_mutex_destroy 3 ,
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.Xr pthread_mutex_init 3 ,
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.Xr pthread_mutex_lock 3 ,
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.Xr pthread_mutex_unlock 3
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.Sh STANDARDS
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The
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.Fn pthread_mutex_trylock
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function conforms to
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.St -p1003.1-96 .
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