Diff: api/SingletonPtr.h

Revision:

144:ef7eb2e8f9f7

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/api/SingletonPtr.h	Fri Sep 02 15:07:44 2016 +0100
@@ -0,0 +1,105 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2013 ARM Limited
+ *
+ * Licensed 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 SINGLETONPTR_H
+#define SINGLETONPTR_H
+
+#include <stdint.h>
+#include <new>
+#include "mbed_assert.h"
+#ifdef MBED_CONF_RTOS_PRESENT
+#include "cmsis_os.h"
+#endif
+
+#ifdef MBED_CONF_RTOS_PRESENT
+extern osMutexId singleton_mutex_id;
+#endif
+
+/** Lock the singleton mutex
+ *
+ * This function is typically used to provide
+ * exclusive access when initializing a
+ * global object.
+ */
+inline static void singleton_lock(void)
+{
+#ifdef MBED_CONF_RTOS_PRESENT
+    osMutexWait(singleton_mutex_id, osWaitForever);
+#endif
+}
+
+/** Unlock the singleton mutex
+ *
+ * This function is typically used to provide
+ * exclusive access when initializing a
+ * global object.
+ */
+inline static void singleton_unlock(void)
+{
+#ifdef MBED_CONF_RTOS_PRESENT
+    osMutexRelease (singleton_mutex_id);
+#endif
+}
+
+/** Utility class for creating an using a singleton
+ *
+ * @Note Synchronization level: Thread safe
+ *
+ * @Note: This class must only be used in a static context -
+ * this class must never be allocated or created on the
+ * stack.
+ *
+ * @Note: This class is lazily initialized on first use.
+ * This class is a POD type so if it is not used it will
+ * be garbage collected.
+ */
+template <class T>
+struct SingletonPtr {
+
+    /** Get a pointer to the underlying singleton
+     *
+     * @returns
+     *   A pointer to the singleton
+     */
+    T* get() {
+        if (NULL == _ptr) {
+            singleton_lock();
+            if (NULL == _ptr) {
+                _ptr = new (_data) T();
+            }
+            singleton_unlock();
+        }
+        // _ptr was not zero initialized or was
+        // corrupted if this assert is hit
+        MBED_ASSERT(_ptr == (T *)&_data);
+        return _ptr;
+    }
+
+    /** Get a pointer to the underlying singleton
+     *
+     * @returns
+     *   A pointer to the singleton
+     */
+    T* operator->() {
+        return get();
+    }
+
+    // This is zero initialized when in global scope
+    T *_ptr;
+    // Force data to be 4 byte aligned
+    uint32_t _data[(sizeof(T) + sizeof(uint32_t) - 1) / sizeof(uint32_t)];
+};
+
+#endif