/* atomic.c : perform atomic initialization * * ==================================================================== * Copyright (c) 2000-2005 CollabNet. All rights reserved. * * This software is licensed as described in the file COPYING, which * you should have received as part of this distribution. The terms * are also available at http://subversion.tigris.org/license-1.html. * If newer versions of this license are posted there, you may use a * newer version instead, at your option. * * This software consists of voluntary contributions made by many * individuals. For exact contribution history, see the revision * history and logs, available at http://subversion.tigris.org/. * ==================================================================== */ #include <apr_time.h> #include "private/svn_atomic.h" /* Magic values for atomic initialization */ #define SVN_ATOMIC_UNINITIALIZED 0 #define SVN_ATOMIC_START_INIT 1 #define SVN_ATOMIC_INIT_FAILED 2 #define SVN_ATOMIC_INITIALIZED 3 svn_error_t* svn_atomic__init_once(volatile svn_atomic_t *global_status, svn_error_t *(*init_func)(void*,apr_pool_t*), void *baton, apr_pool_t* pool) { /* !! Don't use localizable strings in this function, because these !! might cause deadlocks. This function can be used to initialize !! libraries that are used for generating error messages. */ /* We have to call init_func exactly once. Because APR doesn't have statically-initialized mutexes, we implement a poor man's spinlock using svn_atomic_cas. */ svn_atomic_t status = svn_atomic_cas(global_status, SVN_ATOMIC_START_INIT, SVN_ATOMIC_UNINITIALIZED); if (status == SVN_ATOMIC_UNINITIALIZED) { svn_error_t *err = init_func(baton, pool); if (err) { #if APR_HAS_THREADS /* Tell other threads that the initialization failed. */ svn_atomic_cas(global_status, SVN_ATOMIC_INIT_FAILED, SVN_ATOMIC_START_INIT); #endif return svn_error_create(SVN_ERR_ATOMIC_INIT_FAILURE, err, "Couldn't perform atomic initialization"); } svn_atomic_cas(global_status, SVN_ATOMIC_INITIALIZED, SVN_ATOMIC_START_INIT); } #if APR_HAS_THREADS /* Wait for whichever thread is performing initialization to finish. */ /* XXX FIXME: Should we have a maximum wait here, like we have in the Windows file IO spinner? */ else while (status != SVN_ATOMIC_INITIALIZED) { if (status == SVN_ATOMIC_INIT_FAILED) return svn_error_create(SVN_ERR_ATOMIC_INIT_FAILURE, NULL, "Couldn't perform atomic initialization"); apr_sleep(APR_USEC_PER_SEC / 1000); status = svn_atomic_cas(global_status, SVN_ATOMIC_UNINITIALIZED, SVN_ATOMIC_UNINITIALIZED); } #endif /* APR_HAS_THREADS */ return SVN_NO_ERROR; }