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 SYNOPSIS 35.Fd #include <dlfcn.h> 36.Ft void 37.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)" 38.Sh DESCRIPTION 39.Bf Sy 40This interface is experimental. It may be changed or eliminated in 41future releases. 42.Ef 43.Pp 44Threads packages can call 45.Nm 46at initialization time to register locking functions for the dynamic 47linker to use. This enables the dynamic linker to prevent multiple 48threads from entering its critical sections simultaneously. 49.Pp 50The 51.Fa context 52parameter specifies an opaque context for creating locks. The 53dynamic linker will pass it to the 54.Fa lock_create 55function when creating the locks it needs. When the dynamic linker 56is permanently finished using the locking functions (e.g., if the 57program makes a subsequent call to 58.Nm 59to register new locking functions) it will call 60.Fa context_destroy 61to destroy the context. 62.Pp 63The 64.Fa lock_create 65parameter specifies a function for creating a read/write lock. It 66must return a pointer to the new lock. 67.Pp 68The 69.Fa rlock_acquire 70and 71.Fa wlock_acquire 72parameters specify functions which lock a lock for reading or 73writing, respectively. The 74.Fa lock_release 75parameter specifies a function which unlocks a lock. Each of these 76functions is passed a pointer to the lock. 77.Pp 78The 79.Fa lock_destroy 80parameter specifies a function to destroy a lock. It may be 81.Dv NULL 82if locks do not need to be destroyed. The 83.Fa context_destroy 84parameter specifies a function to destroy the context. It may be 85.Dv NULL 86if the context does not need to be destroyed. 87.Pp 88Until 89.Nm 90is called, the dynamic linker protects its critical sections using 91a default locking mechanism which works by blocking the 92.Dv SIGVTALRM , 93.Dv SIGPROF , 94and 95.Dv SIGALRM 96signals. This is sufficient for many application level threads 97packages, which typically use one of these signals to implement 98preemption. An application which has registered its own locking 99methods with 100.Nm 101can restore the default locking by calling 102.Nm 103with all arguments 104.Dv NULL . 105.Sh SEE ALSO 106.Xr rtld 1 , 107.Xr signal 3 108.Sh HISTORY 109The 110.Nm 111function first appeared in FreeBSD 4.0. 112