214 lines
5.7 KiB
Groff
214 lines
5.7 KiB
Groff
.\" $NetBSD: pthread_spin.3,v 1.6 2017/10/22 16:37:24 abhinav Exp $
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.\"
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.\" Copyright (c) 2002, 2008, 2010 The NetBSD Foundation, Inc.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" ----------------------------------------------------------------------------
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.Dd July 8, 2010
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.Dt PTHREAD_SPIN 3
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.Os
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.Sh NAME
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.Nm pthread_spin ,
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.Nm pthread_spin_init ,
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.Nm pthread_spin_destroy ,
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.Nm pthread_spin_lock ,
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.Nm pthread_spin_trylock ,
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.Nm pthread_spin_unlock
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.Nd spin lock interface
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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_spin_init "pthread_spinlock_t *lock" "int pshared"
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.Ft int
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.Fn pthread_spin_destroy "pthread_spinlock_t *lock"
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.Ft int
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.Fn pthread_spin_lock "pthread_spinlock_t *lock"
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.Ft int
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.Fn pthread_spin_trylock "pthread_spinlock_t *lock"
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.Ft int
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.Fn pthread_spin_unlock "pthread_spinlock_t *lock"
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.\" ----------------------------------------------------------------------------
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.Sh DESCRIPTION
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The
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.Fn pthread_spin_init
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function is used to initialize a spin lock.
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In the
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.Nx
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implementation the
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.Fa pshared
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parameter is currently unused and all spin locks exhibit the
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.Dv PTHREAD_PROCESS_SHARED
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property, implying that all spin locks may be
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accessed by threads of multiple processes.
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The results of calling
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.Fn pthread_spin_init
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with an already initialized lock are undefined.
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.Pp
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.\" -----
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The
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.Fn pthread_spin_destroy
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function is used to destroy a spin lock previously created with
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.Fn pthread_spin_init .
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It is undefined what happens if the function is called
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when a thread holds the lock, or if the function is called
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with an uninitialized spin lock.
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.Pp
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.\" -----
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The
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.Fn pthread_spin_lock
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function acquires a spin lock on
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.Fa lock ,
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provided that
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.Fa lock
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is not presently held.
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If the lock cannot be
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immediately acquired, the calling thread repeatedly retries until it can
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acquire the lock.
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Undefined behavior may follow if the calling thread holds
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the lock at the time the call is made.
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.Pp
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The
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.Fn pthread_spin_trylock
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function performs the same locking action, but does not block if the lock
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cannot be immediately obtained; if the lock is held, the call fails.
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.Pp
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.\" -----
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The
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.Fn pthread_spin_unlock
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function is used to release the read/write lock previously obtained by
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.Fn pthread_spin_lock
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or
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.Fn pthread_spin_trylock .
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The results are undefined if the lock is not held by the calling thread.
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.\" ----------------------------------------------------------------------------
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.Sh RETURN VALUES
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If successful, all described functions return zero.
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Otherwise an error number will be returned to indicate the error.
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.Sh ERRORS
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The
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.Fn pthread_spin_init
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function shall fail if:
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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Insufficient memory exists to initialize the lock.
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.El
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.Pp
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The
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.Fn pthread_spin_init
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa lock
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parameter was
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.Dv NULL
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or the
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.Fa pshared
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parameter was neither
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.Dv PTHREAD_PROCESS_SHARED
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nor
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.Dv PTHREAD_PROCESS_PRIVATE .
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.El
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.Pp
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.\" -----
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The
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.Fn pthread_spin_destroy
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EBUSY
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The system has detected an attempt to destroy the object referenced by
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.Fa lock
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while it is locked.
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.It Bq Er EINVAL
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The value specified by
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.Fa lock
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is invalid.
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.El
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.Pp
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.\" -----
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The
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.Fn pthread_spin_trylock
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function shall fail if:
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.Bl -tag -width Er
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.It Bq Er EBUSY
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The lock could not be acquired because a writer holds the lock or
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was blocked on it.
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.El
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.Pp
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The
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.Fn pthread_spin_lock
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EDEADLK
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The current thread already owns
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.Fa lock
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for writing.
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.El
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.Pp
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The
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.Fn pthread_spin_lock
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and
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.Fn pthread_spin_trylock
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functions may fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The value specified by
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.Fa lock
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is invalid.
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.El
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.Pp
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.\" -----
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The
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.Fn pthread_spin_unlock
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The value specified by
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.Fa lock
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is invalid.
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.El
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.\" ----------------------------------------------------------------------------
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.Sh SEE ALSO
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.Xr pthread 3 ,
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.Xr pthread_barrier 3 ,
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.Xr pthread_cond 3 ,
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.Xr pthread_mutex 3 ,
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.Xr pthread_rwlock 3
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.Sh STANDARDS
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These functions conform to
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.St -p1003.1-2001 .
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.\" ----------------------------------------------------------------------------
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.Sh CAVEATS
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Applications using spin locks are vulnerable to the effects of priority
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inversion.
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Applications using real-time threads
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.Pq Dv SCHED_FIFO ,
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.Pq Dv SCHED_RR
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should not use these interfaces.
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Outside carefully controlled environments, priority inversion with spin locks
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can lead to system deadlock.
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Mutexes are preferable in nearly every possible use case.
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