Implement the Blink part of the Device Motion API.

Source/modules/device_orientation/DeviceMotionDispatcher.cpp

+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
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+ * notice, this list of conditions and the following disclaimer.
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+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "DeviceMotionDispatcher.h"
+
+#include <public/Platform.h>
+#include <public/WebDeviceMotionData.h>
+#include <public/WebDeviceMotionHandler.h>
+#include "modules/device_orientation/DeviceMotionController.h"
+#include "modules/device_orientation/DeviceMotionData.h"
+
+namespace WebCore {
+
+// static
+DeviceMotionDispatcher& DeviceMotionDispatcher::shared()
+{
+    DEFINE_STATIC_LOCAL(DeviceMotionDispatcher, deviceMotionDispatcher, ());
+    return deviceMotionDispatcher;
+}
+
+DeviceMotionDispatcher::DeviceMotionDispatcher()
+{
+}
+
+void DeviceMotionDispatcher::addController(DeviceMotionController* controller)
+{
+    bool wasEmpty = m_controllers.isEmpty();
+    m_controllers.add(controller);
+    if (wasEmpty)
+        startListening();
+}
+
+void DeviceMotionDispatcher::removeController(DeviceMotionController* controller)
+{
+    m_controllers.remove(controller);
+    if (m_controllers.isEmpty())
+        stopListening();
+}
+
+void DeviceMotionDispatcher::startListening()
+{
+    if (WebKit::WebDeviceMotionHandler* handler = WebKit::Platform::current()->deviceMotionHandler())
+        handler->startListeningToDeviceMotion(this);
+}
+
+void DeviceMotionDispatcher::stopListening()
+{
+    if (WebKit::WebDeviceMotionHandler* handler = WebKit::Platform::current()->deviceMotionHandler())
+        handler->stopListeningToDeviceMotion();
+}
+
+void DeviceMotionDispatcher::didChangeDeviceMotion(const WebKit::WebDeviceMotionData& motion)
+{
+    m_lastDeviceMotionData = PassRefPtr<WebCore::DeviceMotionData>(motion);
+
+    Vector<DeviceMotionController*> listenerVector;
+    copyToVector(m_controllers, listenerVector);
+    for (size_t i = 0; i < listenerVector.size(); ++i)
+        listenerVector[i]->didChangeDeviceMotion(m_lastDeviceMotionData.get());

[abarth-chromium, 2013/05/07 20:10:01]

It's a re-entrancy issue rather than a concurrency issue.  Suppose
didChangeDeviceMotion causes some script to execute which causes a Document to
be destroy which causes the next DeviceMotionController in the iteration to be
destroyed.  Now you're going to call a function on a dead object.

Copying the raw pointers into a local variable doesn't help you in this
situation....

Instead, you need to iterate m_controllers directly (using indexes) and instead
of removing elements in DeviceMotionDispatcher::removeController, you need to
zero them out.  That way you'll still iterate all the elements of the
m_controllers vector and you can skip the ones that die during the iteration.

After the iteration is done, you can compact m_controllers to get rid of the
zero entries.

[timvolodine, 2013/05/08 12:19:24]

Done.

+}
+
+DeviceMotionData* DeviceMotionDispatcher::latestDeviceMotionData()
+{
+    return m_lastDeviceMotionData.get();
+}
+
+DeviceMotionDispatcher::~DeviceMotionDispatcher()
+{
+}
+
+}  // namespace WebKit