1 files changed, 85 insertions, 0 deletions
diff --git a/subversion/libsvn_subr/atomic.c b/subversion/libsvn_subr/atomic.c
new file mode 100644
index 0000000..b760da4
--- /dev/null
+++ b/subversion/libsvn_subr/atomic.c
@@ -0,0 +1,85 @@
+/* atomic.c : perform atomic initialization
+ *
+ * ====================================================================
+ *    Licensed to the Apache Software Foundation (ASF) under one
+ *    or more contributor license agreements.  See the NOTICE file
+ *    distributed with this work for additional information
+ *    regarding copyright ownership.  The ASF licenses this file
+ *    to you under the Apache License, Version 2.0 (the
+ *    "License"); you may not use this file except in compliance
+ *    with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing,
+ *    software distributed under the License is distributed on an
+ *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *    KIND, either express or implied.  See the License for the
+ *    specific language governing permissions and limitations
+ *    under the License.
+ * ====================================================================
+ */
+
+#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;
+}