text: /*
   * Copyright (C) 2014 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:
   *
   *     * 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/PurgeableVector.h"
  
  #include "public/platform/Platform.h"
  #include "public/platform/WebDiscardableMemory.h"
  #include "wtf/Assertions.h"
  #include "wtf/OwnPtr.h"
  #include "wtf/PassOwnPtr.h"
  
  #include <cstring>
  
  namespace blink {
  
  // WebDiscardableMemory allocations are expensive and page-grained. We only use
  // them when there's a reasonable amount of memory to be saved by the OS
  // discarding the memory.
  static const size_t minimumDiscardableAllocationSize = 4 * 4096;
  
  PurgeableVector::PurgeableVector(PurgeableOption purgeable)
      : m_discardableCapacity(0)
      , m_discardableSize(0)
      , m_isPurgeable(purgeable == Purgeable)
      , m_locksCount(1) // The buffer is locked at creation.
  {
  }
  
  PurgeableVector::~PurgeableVector()
  {
  }
  
  void PurgeableVector::reserveCapacity(size_t capacity)
  {
      ASSERT(isLocked());
  
      if (m_isPurgeable) {
          if (reservePurgeableCapacity(capacity, UseExactCapacity))
              return;
          // Fallback to non-purgeable buffer allocation in case discardable memory allocation failed.
      }
  
      if (!m_vector.capacity()) {
          // Using reserveInitialCapacity() on the underlying vector ensures that the vector uses the
          // exact specified capacity to avoid consuming too much memory for small resources.
          m_vector.reserveInitialCapacity(capacity);
      } else {
          m_vector.reserveCapacity(capacity);
      }
  
      moveDataFromDiscardableToVector();
  }
  
  void PurgeableVector::moveDataFromDiscardableToVector()
  {
      if (m_discardable) {
          m_vector.append(static_cast<const char*>(m_discardable->data()), m_discardableSize);
          clearDiscardable();
      }
  }
  
  void PurgeableVector::clearDiscardable()
  {
      m_discardable.clear();
      m_discardableCapacity = 0;
      m_discardableSize = 0;
  }
  
  void PurgeableVector::append(const char* data, size_t length)
  {
      ASSERT(isLocked());
  
      if (!m_isPurgeable) {
          m_vector.append(data, length);
          return;
      }
  
      const size_t currentSize = m_discardable ? m_discardableSize : m_vector.size();
      const size_t newBufferSize = currentSize + length;
  
      if (!reservePurgeableCapacity(newBufferSize, UseExponentialGrowth)) {
          moveDataFromDiscardableToVector();
          m_vector.append(data, length);
          return;
      }
  
      ASSERT(m_discardableSize + length <= m_discardableCapacity);
      memcpy(static_cast<char*>(m_discardable->data()) + m_discardableSize, data, length);
      m_discardableSize += length;
  }
  
  void PurgeableVector::grow(size_t newSize)
  {
      ASSERT(newSize >= size());
  
      if (m_isPurgeable) {
          if (reservePurgeableCapacity(newSize, UseExponentialGrowth)) {
              m_discardableSize = newSize;
              return;
          }
          moveDataFromDiscardableToVector();
      }
  
      m_vector.resize(newSize);
  }
  
  void PurgeableVector::clear()
  {
      clearDiscardable();
      m_vector.clear();
  }
  
  char* PurgeableVector::data()
  {
      ASSERT(isLocked());
      return m_discardable ? static_cast<char*>(m_discardable->data()) : m_vector.data();
  }
  
  size_t PurgeableVector::size() const
  {
      return m_discardable ? m_discardableSize : m_vector.size();
  }
  
  void PurgeableVector::adopt(Vector<char>& other)
  {
      if (size() > 0)
          clear();
  
      if (!m_isPurgeable) {
          m_vector.swap(other);
          return;
      }
  
      if (other.isEmpty())
          return;
  
      append(other.data(), other.size());
      other.clear();
  }
  
  bool PurgeableVector::lock()
  {
      ++m_locksCount;
      if (m_locksCount > 1)
          return true;
  
      ASSERT(m_locksCount == 1);
      if (!m_discardable)
          return true;
  
      return m_discardable->lock();
  }
  
  void PurgeableVector::unlock()
  {
      ASSERT(isLocked());
      --m_locksCount;
      if (m_locksCount > 0)
          return;
  
      if (!m_vector.isEmpty()) {
          ASSERT(!m_discardable);
          m_isPurgeable = true;
          if (!reservePurgeableCapacity(m_vector.size(), UseExactCapacity))
              return;
      }
  
      if (m_discardable)
          m_discardable->unlock();
  }
  
  bool PurgeableVector::isLocked() const
  {
      ASSERT(m_locksCount >= 0);
      return m_locksCount > 0;
  }
  
  bool PurgeableVector::reservePurgeableCapacity(size_t capacity, PurgeableAllocationStrategy allocationStrategy)
  {
      ASSERT(m_isPurgeable);
  
      if (m_discardable && m_discardableCapacity >= capacity) {
          ASSERT(!m_vector.capacity());
          return true;
      }
  
      if (capacity < minimumDiscardableAllocationSize)
          return false;
  
      if (allocationStrategy == UseExponentialGrowth)
          capacity = adjustPurgeableCapacity(capacity);
  
      OwnPtr<blink::WebDiscardableMemory> discardable = adoptPtr(
          blink::Platform::current()->allocateAndLockDiscardableMemory(capacity));
      if (!discardable) {
          // Discardable memory is not supported.
          m_isPurgeable = false;
          return false;
      }
  
      m_discardableCapacity = capacity;
      // Copy the data that was either in the previous purgeable buffer or in the vector to the new
      // purgeable buffer.
      if (m_discardable) {
          memcpy(discardable->data(), m_discardable->data(), m_discardableSize);
      } else {
          memcpy(discardable->data(), m_vector.data(), m_vector.size());
          m_discardableSize = m_vector.size();
          m_vector.clear();
      }
  
      m_discardable.swap(discardable);
      ASSERT(!m_vector.capacity());
      return true;
  }
  
  size_t PurgeableVector::adjustPurgeableCapacity(size_t capacity) const
  {
      ASSERT(capacity >= minimumDiscardableAllocationSize);
  
      const float growthFactor = 1.5;
      size_t newCapacity = std::max(capacity, static_cast<size_t>(m_discardableCapacity * growthFactor));
  
      // Discardable memory has page-granularity so align to the next page here to minimize
      // fragmentation.
      // Since the page size is only used below to minimize fragmentation it's still safe to use it
      // even if it gets out of sync (e.g. due to the use of huge pages).
      const size_t kPageSize = 4096;
      newCapacity = (newCapacity + kPageSize - 1) & ~(kPageSize - 1);
  
      return std::max(capacity, newCapacity); // Overflow check.
  }
  
  } // namespace blink
  