Add DiscardableMemoryAllocator to work around FD limit issue.

base/memory/discardable_memory_allocator_android.h

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
+#define BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
+
+#include <string>
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
+
+namespace base {
+
+class DiscardableMemory;
+
+namespace internal {
+
+// On Android ashmem is used to implement discardable memory. It is backed by a
+// file (descriptor) thus is a limited resource. This allocator minimizes the
+// problem by allocating large ashmem regions internally and returning smaller
+// chunks to the client.
+// Allocated chunks are systematically aligned on a page boundary therefore this
+// allocator should not be used for small allocations.
+//
+// Threading: The allocator must be deleted on the thread it was constructed on
+// although its Allocate() method can be invoked on any thread. See
+// discardable_memory.h for DiscardableMemory's threading guarantees.
+class BASE_EXPORT_PRIVATE DiscardableMemoryAllocator {
+ public:
+  // Exposed for testing.
+  enum {
+    kMinAshmemRegionSize = 32 * 1024 * 1024,
+  };
+
+  // Note that |name| is only used for debugging/measurement purposes.
+  explicit DiscardableMemoryAllocator(const std::string& name);
+  ~DiscardableMemoryAllocator();
+
+  // Note that the allocator must outlive the returned DiscardableMemory
+  // instance.
+  scoped_ptr<DiscardableMemory> Allocate(size_t size);
+
+ private:
+  class AshmemRegion;
+  class DiscardableAshmemChunk;
+
+  void DeleteAshmemRegion_Locked(AshmemRegion* region);
+
+  base::ThreadChecker thread_checker_;
+  const std::string name_;
+  base::Lock lock_;
+  ScopedVector<AshmemRegion> ashmem_regions_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAllocator);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_