dllockinit(3) [freebsd man page]
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 creat- ing 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 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 registered its own locking methods with dllockinit() can restore the default lock- ing 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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PTHREAD_SPIN(3) BSD Library Functions Manual PTHREAD_SPIN(3) NAME
pthread_spin -- spin lock interface LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> int pthread_spin_init(pthread_spinlock_t *lock, int pshared); int pthread_spin_destroy(pthread_spinlock_t *lock); int pthread_spin_lock(pthread_spinlock_t *lock); int pthread_spin_trylock(pthread_spinlock_t *lock); int pthread_spin_unlock(pthread_spinlock_t *lock); DESCRIPTION
The pthread_spin_init() function is used to initialize a spin lock. In the NetBSD implementation the pshared parameter is currently unused and all spin locks exhibit the PTHREAD_PROCESS_SHARED property, implying that all spin locks may be accessed by threads of multiple pro- cesses. The results of calling pthread_spin_init() with an already initialized lock are undefined. The pthread_spin_destroy() function is used to destroy a spin lock previously created with pthread_spin_init(). It is undefined what happens if the function is called when a thread holds the lock, or if the function is called with an uninitialized spin lock. The pthread_spin_lock() function acquires a spin lock on lock, provided that lock is not presently held. If the lock cannot be immediately acquired, the calling thread repeatedly retries until it can acquire the lock. Undefined behavior may follow if the calling thread holds the lock at the time the call is made. The pthread_spin_trylock() function performs the same locking action, but does not block if the lock cannot be immediately obtained; if the lock is held, the call fails. The pthread_spin_unlock() function is used to release the read/write lock previously obtained by pthread_spin_lock() or pthread_spin_trylock(). The results are undefined if the lock is not held by the calling thread. RETURN VALUES
If successful, all described functions return zero. Otherwise an error number will be returned to indicate the error. ERRORS
The pthread_spin_init() function shall fail if: [ENOMEM] Insufficient memory exists to initialize the lock. The pthread_spin_init() function may fail if: [EINVAL] The lock parameter was NULL or the pshared parameter was neither PTHREAD_PROCESS_SHARED nor PTHREAD_PROCESS_PRIVATE. The pthread_spin_destroy() function may fail if: [EBUSY] The system has detected an attempt to destroy the object referenced by lock while it is locked. [EINVAL] The value specified by lock is invalid. The pthread_spin_trylock() function shall fail if: [EBUSY] The lock could not be acquired because a writer holds the lock or was blocked on it. The pthread_spin_lock() function may fail if: [EDEADLK] The current thread already owns lock for writing. The pthread_spin_lock() and pthread_spin_trylock() functions may fail if: [EINVAL] The value specified by lock is invalid. The pthread_spin_unlock() function may fail if: [EINVAL] The value specified by lock is invalid. SEE ALSO
pthread(3), pthread_barrier(3), pthread_cond(3), pthread_mutex(3), pthread_rwlock(3) STANDARDS
These functions conform to IEEE Std 1003.1-2001 (``POSIX.1''). CAVEATS
Applications using spin locks are vulnerable to the effects of priority inversion. Applications using real-time threads (SCHED_FIFO), (SCHED_RR) should not use these interfaces. Outside carefully controlled environments, priority inversion with spin locks can lead to system deadlock. Mutexes are preferable in nearly every possible use case. BSD
July 8, 2010 BSD