dllockinit man page on FreeBSD

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DLLOCKINIT(3)		 BSD Library Functions Manual		 DLLOCKINIT(3)

NAME
     dllockinit — register thread locking methods with the dynamic 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 enables the
     dynamic linker to prevent multiple threads from entering its critical
     sections simultaneously.

     The context argument 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 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 functions which
     lock a lock for reading or writing, respectively.	The lock_release argu‐
     ment 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 argu‐
     ment 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 sig‐
     nals 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.

BSD				 July 5, 2000				   BSD
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