107 lines
3.6 KiB
Groff
107 lines
3.6 KiB
Groff
.\"
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.\" Copyright (c) 1999 John D. Polstra
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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 AUTHOR 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 AUTHOR 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 December 26, 1999
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.Os FreeBSD
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.Dt DLLOCKINIT 3
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.Sh NAME
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.Nm dllockinit
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.Nd register thread locking methods with the dynamic linker
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.Sh SYNOPSIS
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.Fd #include <dlfcn.h>
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.Ft void
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.Fn dllockinit "void *context" "void *(*lock_create)(void *context)" "void (*rlock_acquire)(void *lock)" "void (*wlock_acquire)(void *lock)" "void (*lock_release)(void *lock)" "void (*lock_destroy)(void *lock)" "void (*context_destroy)(void *context)"
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.Sh DESCRIPTION
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Threads packages can call
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.Nm
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at initialization time to register locking functions for the dynamic
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linker to use. This enables the dynamic linker to prevent multiple
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threads from entering its critical sections simultaneously.
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.Pp
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The
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.Fa context
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parameter specifies an opaque context for creating locks. The
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dynamic linker will pass it to the
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.Fa lock_create
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function when creating the locks it needs. When the dynamic linker
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is permanently finished using the locking functions (e.g., if the
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program makes a subsequent call to
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.Nm
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to register new locking functions) it will call
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.Fa context_destroy
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to destroy the context.
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.Pp
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The
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.Fa lock_create
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parameter specifies a function for creating a read/write lock. It
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must return a pointer to the new lock.
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.Pp
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The
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.Fa rlock_acquire
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and
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.Fa wlock_acquire
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parameters specify functions which lock a lock for reading or
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writing, respectively. The
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.Fa lock_release
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parameter specifies a function which unlocks a lock. Each of these
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functions is passed a pointer to the lock.
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.Pp
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The
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.Fa lock_destroy
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parameter specifies a function to destroy a lock. It may be
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.Dv NULL
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if locks do not need to be destroyed. The
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.Fa context_destroy
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parameter specifies a function to destroy the context. It may be
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.Dv NULL
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if the context does not need to be destroyed.
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.Pp
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Until
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.Nm
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is called, the dynamic linker protects its critical sections using
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a default locking mechanism which works by blocking the
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.Dv SIGVTALRM ,
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.Dv SIGPROF ,
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and
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.Dv SIGALRM
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signals. This is sufficient for many application level threads
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packages, which typically use one of these signals to implement
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preemption. An application which has registered its own locking
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methods with
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.Nm
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can restore the default locking by calling
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.Nm
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with all arguments
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.Dv NULL .
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.Sh SEE ALSO
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.Xr rtld 1 ,
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.Xr signal 3
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.Sh HISTORY
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The
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.Nm
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function first appeared in FreeBSD 4.0.
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