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+/**
+ * @copyright
+ * ====================================================================
+ *    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.
+ * ====================================================================
+ * @endcopyright
+ *
+ * @file svn_atomic.h
+ * @brief Macros and functions for atomic operations
+ */
+
+#ifndef SVN_ATOMIC_H
+#define SVN_ATOMIC_H
+
+#include <apr_version.h>
+#include <apr_atomic.h>
+
+#include "svn_error.h"
+#include "private/svn_dep_compat.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/**
+ * @name Macro definitions for atomic types and operations
+ *
+ * @note These are necessary because the apr_atomic API changed somewhat
+ *       between apr-0.x and apr-1.x.
+ * @{
+ */
+
+/** The type used by all the other atomic operations. */
+#if APR_VERSION_AT_LEAST(1, 0, 0)
+#define svn_atomic_t apr_uint32_t
+#else
+#define svn_atomic_t apr_atomic_t
+#endif
+
+/** Atomically read an #svn_atomic_t from memory. */
+#if APR_VERSION_AT_LEAST(1, 0, 0)
+#define svn_atomic_read(mem) apr_atomic_read32((mem))
+#else
+#define svn_atomic_read(mem) apr_atomic_read((mem))
+#endif
+
+/** Atomically set an #svn_atomic_t in memory. */
+#if APR_VERSION_AT_LEAST(1, 0, 0)
+#define svn_atomic_set(mem, val) apr_atomic_set32((mem), (val))
+#else
+#define svn_atomic_set(mem, val) apr_atomic_set((mem), (val))
+#endif
+
+/** Atomically increment an #svn_atomic_t. */
+#if APR_VERSION_AT_LEAST(1, 0, 0)
+#define svn_atomic_inc(mem) apr_atomic_inc32(mem)
+#else
+#define svn_atomic_inc(mem) apr_atomic_inc(mem)
+#endif
+
+/** Atomically decrement an #svn_atomic_t. */
+#if APR_VERSION_AT_LEAST(1, 0, 0)
+#define svn_atomic_dec(mem) apr_atomic_dec32(mem)
+#else
+#define svn_atomic_dec(mem) apr_atomic_dec(mem)
+#endif
+
+/**
+ * Atomic compare-and-swap.
+ *
+ * Compare the value that @a mem points to with @a cmp. If they are
+ * the same swap the value with @a with.
+ *
+ * @note svn_atomic_cas should not be combined with the other
+ *       svn_atomic operations.  A comment in apr_atomic.h explains
+ *       that on some platforms, the CAS function is implemented in a
+ *       way that is incompatible with the other atomic operations.
+ */
+#if APR_VERSION_AT_LEAST(1, 0, 0)
+#define svn_atomic_cas(mem, with, cmp) \
+    apr_atomic_cas32((mem), (with), (cmp))
+#else
+#define svn_atomic_cas(mem, with, cmp) \
+    apr_atomic_cas((mem), (with), (cmp))
+#endif
+/** @} */
+
+/**
+ * Call an initialization function in a thread-safe manner.
+ *
+ * @a global_status must be a pointer to a global, zero-initialized
+ * #svn_atomic_t. @a init_func is a pointer to the function that performs
+ * the actual initialization. @a baton and and @a pool are passed on to the
+ * init_func for its use.
+ *
+ * @since New in 1.5.
+ */
+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);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* SVN_ATOMIC_H */