Disallow calling Map on currently-mapped SharedMemory

base/memory/shared_memory_win.cc

 // 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 {
@@ skipping 146 matching lines @@
   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_);
@@ skipping 72 matching lines @@
 void SharedMemory::UnlockDeprecated() {
   DCHECK(lock_ != NULL);
   ReleaseMutex(lock_);
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return mapped_file_;
 }
 
 }  // namespace base