[oilpan]: optimize the way we allocate persistent handles in wrappers.

Source/platform/heap/Handle.cpp

+/*
+ * Copyright (C) 2014 Google Inc. All rights reserved.

[Mads Ager (chromium), 2014/09/02 11:45:48]

Let's use the short copyright header for new files?

[wibling-chromium, 2014/09/02 11:54:25]

Done.

+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * 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
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * 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 "platform/heap/Handle.h"
+
+namespace blink {
+
+bool WrapperPersistentRegion::removeIfNotLast(WrapperPersistentRegion** headPtr)
+{
+    ASSERT(!m_count);
+    // We are the last region in the list if both the region's m_prev and
+    // m_next are 0.
+    if (m_prev == 0 && m_next == 0)
+        return false;
+    if (m_prev) {
+        m_prev->m_next = m_next;
+    } else {
+        ASSERT(*headPtr == this);
+        *headPtr = m_next;
+    }
+    if (m_next)
+        m_next->m_prev = m_prev;
+    m_prev = 0;
+    m_next = 0;
+    return true;
+}
+
+void WrapperPersistentRegion::insertHead(WrapperPersistentRegion** headPtr, WrapperPersistentRegion* newHead)
+{
+    ASSERT(headPtr);
+    WrapperPersistentRegion* oldHead = *headPtr;
+    if (oldHead) {
+        ASSERT(!oldHead->m_prev);
+        oldHead->m_prev = newHead;
+    }
+    newHead->m_prev = 0;
+    newHead->m_next = oldHead;
+    *headPtr = newHead;
+}
+
+WrapperPersistentRegion* WrapperPersistentRegion::removeHead(WrapperPersistentRegion** headPtr)
+{
+    // We only call this if there is at least one element in the list.
+    ASSERT(headPtr && *headPtr);
+    WrapperPersistentRegion* oldHead = *headPtr;
+    ASSERT(!oldHead->m_prev);
+    *headPtr = oldHead->m_next;
+    oldHead->m_next = 0;
+    ASSERT(!(*headPtr) || (*headPtr)->m_prev == oldHead);
+    if (*headPtr)
+        (*headPtr)->m_prev = 0;
+    return oldHead;
+}
+
+void* WrapperPersistentRegion::outOfLineAllocate(ThreadState* state, WrapperPersistentRegion* head)
+{
+    void* persistent = 0;
+    // The caller has already tried allocating in the passed-in region, start
+    // from the next.
+    for (WrapperPersistentRegion* current = head->m_next; current; current = current->m_next) {
+        persistent = current->allocate();
+        if (persistent)
+            return persistent;
+    }
+    ASSERT(!persistent);
+    WrapperPersistentRegion* newRegion = state->addWrapperPersistentRegion();
+    persistent = newRegion->allocate();
+    ASSERT(persistent);
+    return persistent;
+}
+
+}