Disallow calling Map on currently-mapped SharedMemory

base/memory/shared_memory.h

 // Copyright (c) 2012 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_SHARED_MEMORY_H_
 #define BASE_MEMORY_SHARED_MEMORY_H_
 
 #include "build/build_config.h"
 
 #include <string>
@@ skipping 136 matching lines @@
   bool Delete(const std::string& name);
 
   // Opens a shared memory segment based on a name.
   // If read_only is true, opens for read-only access.
   // Returns true on success, false on failure.
   bool Open(const std::string& name, bool read_only);
 
   // Maps the shared memory into the caller's address space.
   // Returns true on success, false otherwise.  The memory address
   // is accessed via the memory() accessor.  The mapped address is guaranteed to
-  // have an alignment of at least MAP_MINIMUM_ALIGNMENT.
+  // have an alignment of at least MAP_MINIMUM_ALIGNMENT. This method will fail
+  // if this object is currently mapped.
   bool Map(size_t bytes) {
     return MapAt(0, bytes);
   }
 
   // Same as above, but with |offset| to specify from begining of the shared
   // memory block to map.
   // |offset| must be alignent to value of |SysInfo::VMAllocationGranularity()|.
   bool MapAt(off_t offset, size_t bytes);
   enum { MAP_MINIMUM_ALIGNMENT = 32 };
 
@@ skipping 139 matching lines @@
   }
 
  private:
   SharedMemory* shared_memory_;
   DISALLOW_COPY_AND_ASSIGN(SharedMemoryAutoLockDeprecated);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_H_