dllockinit(3)

NAME

dllockinit - register thread locking methods with the dynam

ic linker

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <dlfcn.h>
void
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));

DESCRIPTION

Due to enhancements in the dynamic linker, this interface is

no longer
needed. It is deprecated and will be removed from future

releases. In
current releases it still exists, but only as a stub which

does nothing.

Threads packages can call dllockinit() at initialization

time to register
locking functions for the dynamic linker to use. This en

ables the
dynamic linker to prevent multiple threads from entering its

critical
sections simultaneously.

The context argument specifies an opaque context for creat

ing locks. The
dynamic linker will pass it to the lock_create function when

creating the
locks it needs. When the dynamic linker is permanently fin

ished using
the locking functions (e.g., if the program makes a subse

quent call to
dllockinit() to register new locking functions) it will call context_destroy to destroy the context.

The lock_create argument specifies a function for creating a

read/write
lock. It must return a pointer to the new lock.

The rlock_acquire and wlock_acquire arguments specify func

tions which
lock a lock for reading or writing, respectively. The

lock_release argument specifies a function which unlocks a lock. Each of

these functions
is passed a pointer to the lock.

The lock_destroy argument specifies a function to destroy a

lock. It may
be NULL if locks do not need to be destroyed. The

context_destroy argument specifies a function to destroy the context. It may be

NULL if the
context does not need to be destroyed.

Until dllockinit() is called, the dynamic linker protects

its critical
sections using a default locking mechanism which works by

blocking the
SIGVTALRM, SIGPROF, and SIGALRM signals. This is sufficient

for many
application level threads packages, which typically use one

of these signals to implement preemption. An application which has reg

istered its
own locking methods with dllockinit() can restore the de

fault locking by
calling dllockinit() with all arguments NULL.

SEE ALSO

rtld(1), signal(3)

HISTORY

The dllockinit() function first appeared in FreeBSD 4.0.

BSD July 5, 2000

BSD