Copyright (c) 1999, 2000 John D. Polstra
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.Dd July 5, 2000 .Dt DLLOCKINIT 3 .Os .Sh NAME .Nm dllockinit .Nd register thread locking methods with the dynamic linker .Sh LIBRARY .Lb libc .Sh SYNOPSIS n dlfcn.h .Ft void .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)" .Sh DESCRIPTION f Sy 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. .Ef

p Threads packages can call .Fn 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.

p The .Fa context argument specifies an opaque context for creating locks. The dynamic linker will pass it to the .Fa 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 .Fn dllockinit to register new locking functions) it will call .Fa context_destroy to destroy the context.

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

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

p The .Fa lock_destroy argument specifies a function to destroy a lock. It may be .Dv NULL if locks do not need to be destroyed. The .Fa context_destroy argument specifies a function to destroy the context. It may be .Dv NULL if the context does not need to be destroyed.

p Until .Fn dllockinit is called, the dynamic linker protects its critical sections using a default locking mechanism which works by blocking the .Dv SIGVTALRM , .Dv SIGPROF , and .Dv 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 .Fn dllockinit can restore the default locking by calling .Fn dllockinit with all arguments .Dv NULL . .Sh SEE ALSO .Xr rtld 1 , .Xr signal 3 .Sh HISTORY The .Fn dllockinit function first appeared in .Fx 4.0 .