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+/* 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.
+ */
+
+#ifndef APR_ATOMIC_H
+#define APR_ATOMIC_H
+
+/**
+ * @file apr_atomic.h
+ * @brief APR Atomic Operations
+ */
+
+#include "apr.h"
+#include "apr_pools.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @defgroup apr_atomic Atomic Operations
+ * @ingroup APR 
+ * @{
+ */
+
+/**
+ * this function is required on some platforms to initialize the
+ * atomic operation's internal structures
+ * @param p pool
+ * @return APR_SUCCESS on successful completion
+ * @remark Programs do NOT need to call this directly. APR will call this
+ *         automatically from apr_initialize().
+ * @internal
+ */
+APR_DECLARE(apr_status_t) apr_atomic_init(apr_pool_t *p);
+
+/*
+ * Atomic operations on 32-bit values
+ * Note: Each of these functions internally implements a memory barrier
+ * on platforms that require it
+ */
+
+/**
+ * atomically read an apr_uint32_t from memory
+ * @param mem the pointer
+ */
+APR_DECLARE(apr_uint32_t) apr_atomic_read32(volatile apr_uint32_t *mem);
+
+/**
+ * atomically set an apr_uint32_t in memory
+ * @param mem pointer to the object
+ * @param val value that the object will assume
+ */
+APR_DECLARE(void) apr_atomic_set32(volatile apr_uint32_t *mem, apr_uint32_t val);
+
+/**
+ * atomically add 'val' to an apr_uint32_t
+ * @param mem pointer to the object
+ * @param val amount to add
+ * @return old value pointed to by mem
+ */
+APR_DECLARE(apr_uint32_t) apr_atomic_add32(volatile apr_uint32_t *mem, apr_uint32_t val);
+
+/**
+ * atomically subtract 'val' from an apr_uint32_t
+ * @param mem pointer to the object
+ * @param val amount to subtract
+ */
+APR_DECLARE(void) apr_atomic_sub32(volatile apr_uint32_t *mem, apr_uint32_t val);
+
+/**
+ * atomically increment an apr_uint32_t by 1
+ * @param mem pointer to the object
+ * @return old value pointed to by mem
+ */
+APR_DECLARE(apr_uint32_t) apr_atomic_inc32(volatile apr_uint32_t *mem);
+
+/**
+ * atomically decrement an apr_uint32_t by 1
+ * @param mem pointer to the atomic value
+ * @return zero if the value becomes zero on decrement, otherwise non-zero
+ */
+APR_DECLARE(int) apr_atomic_dec32(volatile apr_uint32_t *mem);
+
+/**
+ * compare an apr_uint32_t's value with 'cmp'.
+ * If they are the same swap the value with 'with'
+ * @param mem pointer to the value
+ * @param with what to swap it with
+ * @param cmp the value to compare it to
+ * @return the old value of *mem
+ */
+APR_DECLARE(apr_uint32_t) apr_atomic_cas32(volatile apr_uint32_t *mem, apr_uint32_t with,
+                              apr_uint32_t cmp);
+
+/**
+ * exchange an apr_uint32_t's value with 'val'.
+ * @param mem pointer to the value
+ * @param val what to swap it with
+ * @return the old value of *mem
+ */
+APR_DECLARE(apr_uint32_t) apr_atomic_xchg32(volatile apr_uint32_t *mem, apr_uint32_t val);
+
+/*
+ * Atomic operations on 64-bit values
+ * Note: Each of these functions internally implements a memory barrier
+ * on platforms that require it
+ */
+
+/**
+ * atomically read an apr_uint64_t from memory
+ * @param mem the pointer
+ */
+APR_DECLARE(apr_uint64_t) apr_atomic_read64(volatile apr_uint64_t *mem);
+
+/**
+ * atomically set an apr_uint64_t in memory
+ * @param mem pointer to the object
+ * @param val value that the object will assume
+ */
+APR_DECLARE(void) apr_atomic_set64(volatile apr_uint64_t *mem, apr_uint64_t val);
+
+/**
+ * atomically add 'val' to an apr_uint64_t
+ * @param mem pointer to the object
+ * @param val amount to add
+ * @return old value pointed to by mem
+ */
+APR_DECLARE(apr_uint64_t) apr_atomic_add64(volatile apr_uint64_t *mem, apr_uint64_t val);
+
+/**
+ * atomically subtract 'val' from an apr_uint64_t
+ * @param mem pointer to the object
+ * @param val amount to subtract
+ */
+APR_DECLARE(void) apr_atomic_sub64(volatile apr_uint64_t *mem, apr_uint64_t val);
+
+/**
+ * atomically increment an apr_uint64_t by 1
+ * @param mem pointer to the object
+ * @return old value pointed to by mem
+ */
+APR_DECLARE(apr_uint64_t) apr_atomic_inc64(volatile apr_uint64_t *mem);
+
+/**
+ * atomically decrement an apr_uint64_t by 1
+ * @param mem pointer to the atomic value
+ * @return zero if the value becomes zero on decrement, otherwise non-zero
+ */
+APR_DECLARE(int) apr_atomic_dec64(volatile apr_uint64_t *mem);
+
+/**
+ * compare an apr_uint64_t's value with 'cmp'.
+ * If they are the same swap the value with 'with'
+ * @param mem pointer to the value
+ * @param with what to swap it with
+ * @param cmp the value to compare it to
+ * @return the old value of *mem
+ */
+APR_DECLARE(apr_uint64_t) apr_atomic_cas64(volatile apr_uint64_t *mem, apr_uint64_t with,
+                              apr_uint64_t cmp);
+
+/**
+ * exchange an apr_uint64_t's value with 'val'.
+ * @param mem pointer to the value
+ * @param val what to swap it with
+ * @return the old value of *mem
+ */
+APR_DECLARE(apr_uint64_t) apr_atomic_xchg64(volatile apr_uint64_t *mem, apr_uint64_t val);
+
+/**
+ * compare the pointer's value with cmp.
+ * If they are the same swap the value with 'with'
+ * @param mem pointer to the pointer
+ * @param with what to swap it with
+ * @param cmp the value to compare it to
+ * @return the old value of the pointer
+ */
+APR_DECLARE(void*) apr_atomic_casptr(volatile void **mem, void *with, const void *cmp);
+
+/**
+ * exchange a pair of pointer values
+ * @param mem pointer to the pointer
+ * @param with what to swap it with
+ * @return the old value of the pointer
+ */
+APR_DECLARE(void*) apr_atomic_xchgptr(volatile void **mem, void *with);
+
+/** @} */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif	/* !APR_ATOMIC_H */