root/base/memory/shared_memory_win.cc

DEFINITIONS

1. GetMemorySectionSize
2. lock_
3. name_
4. lock_
5. lock_
6. IsHandleValid
7. NULLHandle
8. CloseHandle
9. GetHandleLimit
10. CreateAndMapAnonymous
11. Create
12. Delete
13. Open
14. MapAt
15. Unmap
16. ShareToProcessCommon
17. Close
18. LockDeprecated
19. UnlockDeprecated
20. handle

// 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.

#include "base/memory/shared_memory.h"

#include "base/logging.h"
#include "base/strings/utf_string_conversions.h"

namespace {

// Returns the length of the memory section starting at the supplied address.
size_t GetMemorySectionSize(void* address) {
  MEMORY_BASIC_INFORMATION memory_info;
  if (!::VirtualQuery(address, &memory_info, sizeof(memory_info)))
    return 0;
  return memory_info.RegionSize - (static_cast<char*>(address) -
         static_cast<char*>(memory_info.AllocationBase));
}

}  // namespace.

namespace base {

SharedMemory::SharedMemory()
    : mapped_file_(NULL),
      memory_(NULL),
      read_only_(false),
      mapped_size_(0),
      requested_size_(0),
      lock_(NULL) {
}

SharedMemory::SharedMemory(const std::wstring& name)
    : mapped_file_(NULL),
      memory_(NULL),
      read_only_(false),
      requested_size_(0),
      mapped_size_(0),
      lock_(NULL),
      name_(name) {
}

SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
    : mapped_file_(handle),
      memory_(NULL),
      read_only_(read_only),
      requested_size_(0),
      mapped_size_(0),
      lock_(NULL) {
}

SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only,
                           ProcessHandle process)
    : mapped_file_(NULL),
      memory_(NULL),
      read_only_(read_only),
      requested_size_(0),
      mapped_size_(0),
      lock_(NULL) {
  ::DuplicateHandle(process, handle,
                    GetCurrentProcess(), &mapped_file_,
                    read_only_ ? FILE_MAP_READ : FILE_MAP_READ |
                        FILE_MAP_WRITE,
                    FALSE, 0);
}

SharedMemory::~SharedMemory() {
  Close();
  if (lock_ != NULL)
    CloseHandle(lock_);
}

// static
bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
  return handle != NULL;
}

// static
SharedMemoryHandle SharedMemory::NULLHandle() {
  return NULL;
}

// static
void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
  DCHECK(handle != NULL);
  ::CloseHandle(handle);
}

// static
size_t SharedMemory::GetHandleLimit() {
  // Rounded down from value reported here:
  // http://blogs.technet.com/b/markrussinovich/archive/2009/09/29/3283844.aspx
  return static_cast<size_t>(1 << 23);
}

bool SharedMemory::CreateAndMapAnonymous(size_t size) {
  return CreateAnonymous(size) && Map(size);
}

bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
  // TODO(bsy,sehr): crbug.com/210609 NaCl forces us to round up 64k here,
  // wasting 32k per mapping on average.
  static const size_t kSectionMask = 65536 - 1;
  DCHECK(!options.executable);
  DCHECK(!mapped_file_);
  if (options.size == 0)
    return false;

  // Check maximum accounting for overflow.
  if (options.size >
      static_cast<size_t>(std::numeric_limits<int>::max()) - kSectionMask)
    return false;

  size_t rounded_size = (options.size + kSectionMask) & ~kSectionMask;
  name_ = ASCIIToWide(options.name_deprecated == NULL ? "" :
                          *options.name_deprecated);
  mapped_file_ = CreateFileMapping(INVALID_HANDLE_VALUE, NULL,
      PAGE_READWRITE, 0, static_cast<DWORD>(rounded_size),
      name_.empty() ? NULL : name_.c_str());
  if (!mapped_file_)
    return false;

  requested_size_ = options.size;

  // Check if the shared memory pre-exists.
  if (GetLastError() == ERROR_ALREADY_EXISTS) {
    // If the file already existed, set requested_size_ to 0 to show that
    // we don't know the size.
    requested_size_ = 0;
    if (!options.open_existing_deprecated) {
      Close();
      return false;
    }
  }

  return true;
}

bool SharedMemory::Delete(const std::string& name) {
  // intentionally empty -- there is nothing for us to do on Windows.
  return true;
}

bool SharedMemory::Open(const std::string& name, bool read_only) {
  DCHECK(!mapped_file_);

  name_ = ASCIIToWide(name);
  read_only_ = read_only;
  mapped_file_ = OpenFileMapping(
      read_only_ ? FILE_MAP_READ : FILE_MAP_READ | FILE_MAP_WRITE,
      false, name_.empty() ? NULL : name_.c_str());
  if (mapped_file_ != NULL) {
    // Note: size_ is not set in this case.
    return true;
  }
  return false;
}

bool SharedMemory::MapAt(off_t offset, size_t bytes) {
  if (mapped_file_ == NULL)
    return false;

  if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
    return false;

  if (memory_)
    return false;

  memory_ = MapViewOfFile(mapped_file_,
                          read_only_ ? FILE_MAP_READ : FILE_MAP_READ |
                              FILE_MAP_WRITE,
                          static_cast<uint64>(offset) >> 32,
                          static_cast<DWORD>(offset),
                          bytes);
  if (memory_ != NULL) {
    DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
        (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
    mapped_size_ = GetMemorySectionSize(memory_);
    return true;
  }
  return false;
}

bool SharedMemory::Unmap() {
  if (memory_ == NULL)
    return false;

  UnmapViewOfFile(memory_);
  memory_ = NULL;
  return true;
}

bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                        SharedMemoryHandle *new_handle,
                                        bool close_self,
                                        ShareMode share_mode) {
  *new_handle = 0;
  DWORD access = FILE_MAP_READ;
  DWORD options = 0;
  HANDLE mapped_file = mapped_file_;
  HANDLE result;
  if (share_mode == SHARE_CURRENT_MODE && !read_only_)
    access |= FILE_MAP_WRITE;
  if (close_self) {
    // DUPLICATE_CLOSE_SOURCE causes DuplicateHandle to close mapped_file.
    options = DUPLICATE_CLOSE_SOURCE;
    mapped_file_ = NULL;
    Unmap();
  }

  if (process == GetCurrentProcess() && close_self) {
    *new_handle = mapped_file;
    return true;
  }

  if (!DuplicateHandle(GetCurrentProcess(), mapped_file, process,
      &result, access, FALSE, options))
    return false;
  *new_handle = result;
  return true;
}


void SharedMemory::Close() {
  if (memory_ != NULL) {
    UnmapViewOfFile(memory_);
    memory_ = NULL;
  }

  if (mapped_file_ != NULL) {
    CloseHandle(mapped_file_);
    mapped_file_ = NULL;
  }
}

void SharedMemory::LockDeprecated() {
  if (lock_ == NULL) {
    std::wstring name = name_;
    name.append(L"lock");
    lock_ = CreateMutex(NULL, FALSE, name.c_str());
    if (lock_ == NULL) {
      DPLOG(ERROR) << "Could not create mutex.";
      NOTREACHED();
      return;  // There is nothing good we can do here.
    }
  }
  DWORD result = WaitForSingleObject(lock_, INFINITE);
  DCHECK_EQ(result, WAIT_OBJECT_0);
}

void SharedMemory::UnlockDeprecated() {
  DCHECK(lock_ != NULL);
  ReleaseMutex(lock_);
}

SharedMemoryHandle SharedMemory::handle() const {
  return mapped_file_;
}

}  // namespace base