Diff: inc/types/RefCounted.h

Revision:

1:8aa5cdb4ab67

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/inc/types/RefCounted.h	Thu Apr 07 01:33:22 2016 +0100
@@ -0,0 +1,72 @@
+/*
+The MIT License (MIT)
+
+Copyright (c) 2016 British Broadcasting Corporation.
+This software is provided by Lancaster University by arrangement with the BBC.
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+*/
+
+#ifndef REF_COUNTED_H
+#define REF_COUNTED_H
+
+#include "mbed.h"
+#include "MicroBitConfig.h"
+#include "MicroBitDevice.h"
+
+/**
+  * Base class for payload for ref-counted objects. Used by ManagedString and MicroBitImage.
+  * There is no constructor, as this struct is typically malloc()ed.
+  */
+struct RefCounted
+{
+public:
+
+    /**
+      * The high 15 bits hold the number of outstanding references. The lowest bit is always 1
+      * to make sure it doesn't look like vtable.
+      * Should never be even or one (object should be deleted then).
+      * When it's set to 0xffff, it means the object sits in flash and should not be counted.
+      */
+    uint16_t refCount;
+
+    /**
+      * Increment reference count.
+      */
+    void incr();
+
+    /**
+      * Decrement reference count.
+      */
+    void decr();
+
+    /**
+      * Initializes for one outstanding reference.
+      */
+    void init();
+
+    /**
+      * Checks if the object resides in flash memory.
+      *
+      * @return true if the object resides in flash memory, false otherwise.
+      */
+    bool isReadOnly();
+};
+
+#endif