DLLOCKINIT(3)

NAME
dllockinit - register thread locking methods with the dynamic linker

LIBRARY
libc

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
This interface is experimental. It may be changed or eliminated in future releases.

Threads packages can call dllockinit at initialization time to register locking functions for the dynamic linker to use. This enables the dynamic linker to prevent multiple threads from entering its critical sections simultaneously.

The context parameter specifies an opaque context for creating locks. The dynamic linker will pass it to the lock_create function when creating the locks it needs. When the dynamic linker is permanently finished using the locking functions (e.g., if the program makes a subsequent call to dllockinit to register new locking functions) it will call context_destroy to destroy the context.

The lock_create parameter specifies a function for creating a read/write lock. It must return a pointer to the new lock.

The rlock_acquire and wlock_acquire parameters specify functions which lock a lock for reading or writing, respectively. The lock_release parameter specifies a function which unlocks a lock. Each of these functions is passed a pointer to the lock.

The lock_destroy parameter specifies a function to destroy a lock. It may be NULL if locks do not need to be destroyed. The context_destroy parameter 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 registered its own locking methods with dllockinit can restore the default locking by calling dllockinit with all arguments NULL.

SEE ALSO
rtld(1), signal(3)

HISTORY
The dllockinit function first appeared in FreeBSD 4.0.