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 December 26, 1999 29.Os FreeBSD 30.Dt DLLOCKINIT 3 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.Fd #include <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 42This interface is experimental. It may be changed or eliminated in 43future releases. 44.Ef 45.Pp 46Threads packages can call 47.Nm 48at initialization time to register locking functions for the dynamic 49linker to use. This enables the dynamic linker to prevent multiple 50threads from entering its critical sections simultaneously. 51.Pp 52The 53.Fa context 54parameter specifies an opaque context for creating locks. The 55dynamic linker will pass it to the 56.Fa lock_create 57function when creating the locks it needs. When the dynamic linker 58is permanently finished using the locking functions (e.g., if the 59program makes a subsequent call to 60.Nm 61to register new locking functions) it will call 62.Fa context_destroy 63to destroy the context. 64.Pp 65The 66.Fa lock_create 67parameter specifies a function for creating a read/write lock. It 68must return a pointer to the new lock. 69.Pp 70The 71.Fa rlock_acquire 72and 73.Fa wlock_acquire 74parameters specify functions which lock a lock for reading or 75writing, respectively. The 76.Fa lock_release 77parameter specifies a function which unlocks a lock. Each of these 78functions is passed a pointer to the lock. 79.Pp 80The 81.Fa lock_destroy 82parameter specifies a function to destroy a lock. It may be 83.Dv NULL 84if locks do not need to be destroyed. The 85.Fa context_destroy 86parameter specifies a function to destroy the context. It may be 87.Dv NULL 88if the context does not need to be destroyed. 89.Pp 90Until 91.Nm 92is called, the dynamic linker protects its critical sections using 93a default locking mechanism which works by blocking the 94.Dv SIGVTALRM , 95.Dv SIGPROF , 96and 97.Dv SIGALRM 98signals. This is sufficient for many application level threads 99packages, which typically use one of these signals to implement 100preemption. An application which has registered its own locking 101methods with 102.Nm 103can restore the default locking by calling 104.Nm 105with all arguments 106.Dv NULL . 107.Sh SEE ALSO 108.Xr rtld 1 , 109.Xr signal 3 110.Sh HISTORY 111The 112.Nm 113function first appeared in FreeBSD 4.0. 114