Implementation of an STL compatible allocator for Courgette on Windows....

courgette/memory_allocator.h

+// Copyright (c) 2011 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 COURGETTE_MEMORY_ALLOCATOR_H_
+#define COURGETTE_MEMORY_ALLOCATOR_H_
+
+#include <memory>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/platform_file.h"
+
+namespace courgette {
+
+#ifdef OS_WIN
+
+// Manages a temporary file.  The file is created in the %TEMP% folder and
+// is deleted when the file handle is closed.
+// NOTE: Since the file will be used as backing for a memory allocation,
+// it will never be so big that size_t cannot represent its size.
+class TempFile {
+ public:
+  TempFile();
+  ~TempFile();
+
+  bool Create();
+  void Close();
+  bool SetSize(size_t size);
+
+  // Returns true iff the temp file is currently open.
+  bool valid() const;
+
+  // Returns the handle of the temporary file or INVALID_HANDLE_VALUE if
+  // a temp file has not been created.
+  base::PlatformFile handle() const;
+
+  // Returns the size of the temp file.  If the temp file doesn't exist,
+  // the return value is 0.
+  size_t size() const;
+
+ protected:
+  base::PlatformFile file_;
+  size_t size_;
+};
+
+// Manages a read/write virtual mapping of a physical file.
+class FileMapping {
+ public:
+  FileMapping();
+  ~FileMapping();
+
+  // Map a file from beginning to |size|.
+  bool Create(HANDLE file, size_t size);
+  void Close();
+
+  // Returns true iff a mapping has been created.
+  bool valid() const;
+
+  // Returns a writable pointer to the beginning of the memory mapped file.
+  // If Create has not been called successfully, return value is NULL.
+  void* view() const;
+
+ protected:
+  HANDLE mapping_;
+  void* view_;
+};
+
+// Manages a temporary file and a memory mapping of the temporary file.
+// The memory that this class manages holds a pointer back to the TempMapping
+// object itself, so that given a memory pointer allocated by this class,
+// you can get a pointer to the TempMapping instance that owns that memory.
+class TempMapping {
+ public:
+  TempMapping();
+  ~TempMapping();
+
+  // Creates a temporary file of size |size| and maps it into the current
+  // process' address space.
+  bool Initialize(size_t size);
+
+  // Returns a writable pointer to the reserved memory.
+  void* memory() const;
+
+  // Returns a pointer to the TempMapping instance that allocated the |mem|
+  // block of memory.  It's the callers responsibility to make sure that
+  // the memory block was allocated by the TempMapping class.
+  static TempMapping* GetMappingFromPtr(void* mem);
+
+ protected:
+  TempFile file_;
+  FileMapping mapping_;
+};
+
+// An STL compatible memory allocator class that allocates memory either
+// from the heap or via a temporary file.  A file allocation will be made
+// if either the requested memory size exceeds |kMaxHeapAllocationSize|
+// or if a heap allocation fails.
+// Allocating the memory as a mapping of a temporary file solves the problem
+// that there might not be enough physical memory and pagefile to support the
+// allocation.  This can happen because these resources are too small, or
+// already committed to other processes.  Provided there is enough disk, the
+// temporary file acts like a pagefile that other processes can't access.
+template<class T>
+class MemoryAllocator {
+ public:
+  typedef T value_type;
+  typedef value_type* pointer;
+  typedef value_type& reference;
+  typedef const value_type* const_pointer;
+  typedef const value_type& const_reference;
+  typedef size_t size_type;
+  typedef ptrdiff_t difference_type;
+
+  // Each allocation is tagged with a single byte so that we know how to
+  // deallocate it.
+  enum AllocationType {
+    HEAP_ALLOCATION,
+    FILE_ALLOCATION,
+  };
+
+  // 5MB is the maximum heap allocation size that we'll attempt.
+  // When applying a patch for Chrome 10.X we found that at this
+  // threshold there were 17 allocations higher than this threshold
+  // (largest at 136MB) 10 allocations just below the threshold and 6362
+  // smaller allocations.
+  static const size_t kMaxHeapAllocationSize = 1024 * 1024 * 5;
+
+  template<class OtherT>
+  struct rebind {
+    // convert an MemoryAllocator<T> to a MemoryAllocator<OtherT>
+    typedef MemoryAllocator<OtherT> other;
+  };
+
+  MemoryAllocator() _THROW0() {
+  }
+
+  explicit MemoryAllocator(const MemoryAllocator<T>& other) _THROW0() {
+  }
+
+  template<class OtherT>
+  explicit MemoryAllocator(const MemoryAllocator<OtherT>& other) _THROW0() {
+  }
+
+  ~MemoryAllocator() {
+  }
+
+  void deallocate(pointer ptr, size_type size) {
+    uint8* mem = reinterpret_cast<uint8*>(ptr);
+    mem -= sizeof(T);
+    if (mem[0] == HEAP_ALLOCATION) {
+      delete [] mem;
+    } else {
+      DCHECK_EQ(static_cast<uint8>(FILE_ALLOCATION), mem[0]);
+      TempMapping* mapping = TempMapping::GetMappingFromPtr(mem);
+      delete mapping;
+    }
+  }
+
+  pointer allocate(size_type count) {
+    // We use the first byte of each allocation to mark the allocation type.
+    // However, so that the allocation is properly aligned, we allocate an
+    // extra element and then use the first byte of the first element
+    // to mark the allocation type.
+    count++;
+
+    if (count > max_size())
+      throw std::length_error("overflow");
+
+    size_type bytes = count * sizeof(T);
+    uint8* mem = NULL;
+
+    // First see if we can do this allocation on the heap.
+    if (count < kMaxHeapAllocationSize)
+      mem = new(std::nothrow) uint8[bytes];
+    if (mem != NULL) {
+      mem[0] = static_cast<uint8>(HEAP_ALLOCATION);
+    } else {
+      // If either the heap allocation failed or the request exceeds the
+      // max heap allocation threshold, we back the allocation with a temp file.
+      TempMapping* mapping = new TempMapping();
+      if (!mapping->Initialize(bytes)) {
+        delete mapping;
+        throw std::bad_alloc("TempMapping::Initialize");
+      }
+      mem = reinterpret_cast<uint8*>(mapping->memory());
+      mem[0] = static_cast<uint8>(FILE_ALLOCATION);
+    }
+    return reinterpret_cast<pointer>(mem + sizeof(T));
+  }
+
+  pointer allocate(size_type count, const void* hint) {
+    return allocate(count);
+  }
+
+  void construct(pointer ptr, const T& value) {
+    ::new(ptr) T(value);
+  }
+
+  void destroy(pointer ptr) {
+    ptr->~T();
+  }
+
+  size_t max_size() const _THROW0() {
+    size_type count = static_cast<size_type>(-1) / sizeof(T);
+    return (0 < count ? count : 1);
+  }
+};
+
+#else  // OS_WIN
+
+// On Mac, Linux, we just use the default STL allocator.
+template<class T>
+class MemoryAllocator : public std::allocator<T> {
+ public:
+};
+
+#endif  // OS_WIN
+
+}  // namespace courgette
+
+#endif  // COURGETTE_MEMORY_ALLOCATOR_H_