1.\" 2.\" Copyright (c) 1999, 2000 John D. Polstra 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd July 5, 2000 29.Dt DLLOCKINIT 3 30.Os 31.Sh NAME 32.Nm dllockinit 33.Nd register thread locking methods with the dynamic linker 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In dlfcn.h 38.Ft void 39.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)" 40.Sh DESCRIPTION 41.Bf Sy 42Due to enhancements in the dynamic linker, this interface is no longer 43needed. 44It is deprecated and will be removed from future releases. 45In current releases it still exists, but only as a stub which does nothing. 46.Ef 47.Pp 48Threads packages can call 49.Fn dllockinit 50at initialization time to register locking functions for the dynamic 51linker to use. 52This enables the dynamic linker to prevent multiple 53threads from entering its critical sections simultaneously. 54.Pp 55The 56.Fa context 57argument specifies an opaque context for creating locks. 58The 59dynamic linker will pass it to the 60.Fa lock_create 61function when creating the locks it needs. 62When the dynamic linker 63is permanently finished using the locking functions (e.g., if the 64program makes a subsequent call to 65.Fn dllockinit 66to register new locking functions) it will call 67.Fa context_destroy 68to destroy the context. 69.Pp 70The 71.Fa lock_create 72argument specifies a function for creating a read/write lock. 73It 74must return a pointer to the new lock. 75.Pp 76The 77.Fa rlock_acquire 78and 79.Fa wlock_acquire 80arguments specify functions which lock a lock for reading or 81writing, respectively. 82The 83.Fa lock_release 84argument specifies a function which unlocks a lock. 85Each of these 86functions is passed a pointer to the lock. 87.Pp 88The 89.Fa lock_destroy 90argument specifies a function to destroy a lock. 91It may be 92.Dv NULL 93if locks do not need to be destroyed. 94The 95.Fa context_destroy 96argument specifies a function to destroy the context. 97It may be 98.Dv NULL 99if the context does not need to be destroyed. 100.Pp 101Until 102.Fn dllockinit 103is called, the dynamic linker protects its critical sections using 104a default locking mechanism which works by blocking the 105.Dv SIGVTALRM , 106.Dv SIGPROF , 107and 108.Dv SIGALRM 109signals. 110This is sufficient for many application level threads 111packages, which typically use one of these signals to implement 112preemption. 113An application which has registered its own locking 114methods with 115.Fn dllockinit 116can restore the default locking by calling 117.Fn dllockinit 118with all arguments 119.Dv NULL . 120.Sh SEE ALSO 121.Xr rtld 1 , 122.Xr signal 3 123.Sh HISTORY 124The 125.Fn dllockinit 126function first appeared in 127.Fx 4.0 . 128