Android should be able to discard CachedResources

Source/core/platform/PurgeableBuffer.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 met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY GOOGLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL GOOGLE INC. 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 "core/platform/PurgeableBuffer.h"
+
+#include "public/platform/Platform.h"
+#include "public/platform/WebDiscardableMemory.h"
+
+#include <string.h>
+
+namespace WebCore {
+
+// WebDiscardableMemory allocations are a limited resource. We only use them
+// when there's a reasonable amount of memory to be saved by the OS discarding
+// the memory.
+static size_t minimumSize = 4 * 4096;
+
+PassOwnPtr<PurgeableBuffer> PurgeableBuffer::create(const char* data, size_t size)
+{
+    if (size < minimumSize)
+        return nullptr;
+
+    OwnPtr<WebKit::WebDiscardableMemory> memory = adoptPtr(WebKit::Platform::current()->allocateAndLockDiscardableMemory(size));
+    if (!memory)
+        return nullptr;
+
+    return adoptPtr(new PurgeableBuffer(memory.release(), data, size));
+}
+
+PurgeableBuffer::~PurgeableBuffer()
+{
+    if (m_state == Locked)
+        m_memory->unlock();
+}
+
+const char* PurgeableBuffer::data() const
+{
+    ASSERT(m_state == Locked);
+    return static_cast<const char*>(m_memory->data());
+}
+
+bool PurgeableBuffer::wasPurged() const
+{
+    return m_state == Purged;
+}
+
+bool PurgeableBuffer::lock()
+{
+    ASSERT(m_state == Unlocked);
+    if (!m_memory->lock()) {
+        m_state = Purged;
+        m_memory = nullptr;
+        return false;
+    }
+    m_state = Locked;
+    return true;
+}
+
+void PurgeableBuffer::unlock()
+{
+    ASSERT(m_state == Locked);
+    m_memory->unlock();
+    m_state = Unlocked;
+}
+
+PurgeableBuffer::PurgeableBuffer(PassOwnPtr<WebKit::WebDiscardableMemory> memory, const char* data, size_t size)
+    : m_memory(memory)
+    , m_size(size)
+    , m_state(Locked)
+{
+    memcpy(m_memory->data(), data, size);
+}
+
+}