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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef SANDBOX_SRC_SHARED_HANDLES_H__
+#define SANDBOX_SRC_SHARED_HANDLES_H__
+
+#include "base/basictypes.h"
+
+#ifndef HANDLE
+// We can provide our own windows compatilble handle definition, but
+// in general we want to rely on the client of this api to include
+// the proper windows headers. Note that we don't want to bring the
+// whole <windows.h> into scope if we don't have to.
+typedef void* HANDLE;
+#endif
+
+namespace sandbox {
+
+// SharedHandles is a simple class to stash and find windows object handles
+// given a raw block of memory which is shared between two processes.
+// It addresses the need to communicate a handle value between two windows
+// processes given that they are already sharing some memory.
+//
+// This class is not exposed directly to users of the sanbox API, instead
+// we expose the wrapper methods TargetProcess::TransferHandle( ) and
+// TargetServices::GetTransferHandle()
+//
+// Use it for a small number of items, since internaly uses linear seach
+//
+// The use is very simple. Given a shared memory between proces A and B:
+// process A:
+//  HANDLE handle = SomeFunction(..);
+//  SharedHandles shared_handes;
+//  shared_handles.Init(memory)
+//  shared_handles.SetHandle(3, handle);
+//
+// process B:
+//  SharedHandles shared_handes;
+//  shared_handles.Init(memory)
+//  HANDLE handle = shared_handles.GetHandle(3);
+//
+// Note that '3' in this example is a unique id, that must be agreed before
+// transfer
+//
+// Note2: While this class can be used in a single process, there are
+// better alternatives such as STL
+//
+// Note3: Under windows a kernel object handle in one process does not
+// make sense for another process unless there is a DuplicateHandle( )
+// call involved which this class DOES NOT do that for you.
+//
+// Note4: Under windows, shared memory when created is initialized to
+// zeros always. If you are not using shared memory it is your responsability
+// to zero it for the setter process and to copy it to the getter process.
+class SharedHandles {
+ public:
+  SharedHandles();
+
+  // Initializes the shared memory for use.
+  // Pass the shared memory base and size. It will internally compute
+  // how many handles can it store. If initialization fails the return value
+  // is false.
+  bool Init(void* raw_mem, size_t size_bytes);
+
+  // Sets a handle in the shared memory for transfer.
+  // Parameters:
+  // tag : an integer, different from zero that uniquely identfies the
+  // handle to transfer.
+  // handle: the handle value associated with 'tag' to tranfer
+  // Returns false if there is not enough space in the shared memory for
+  // this handle.
+  bool SetHandle(uint32 tag, HANDLE handle);
+
+  // Gets a handle previously stored by SetHandle.
+  // Parameters:
+  // tag: an integer different from zero that uniquely identfies the handle
+  // to retrieve.
+  // *handle: output handle value if the call was succesful.
+  // If a handle with the provided tag is not found the return value is false.
+  // If the tag is found the return value is true.
+  bool GetHandle(uint32 tag, HANDLE* handle);
+
+ private:
+  // A single item is the tuple handle/tag
+  struct SharedItem {
+    uint32 tag;
+    void* item;
+  };
+
+  // SharedMem is used to layout the memory as an array of SharedItems
+  struct SharedMem {
+    size_t max_items;
+    SharedItem* items;
+  };
+
+  // Finds an Item tuple provided the handle tag.
+  // Uses linear search because we expect the number of handles to be
+  // small (say less than ~100).
+  SharedItem* FindByTag(uint32 tag);
+
+  SharedMem shared_;
+  DISALLOW_EVIL_CONSTRUCTORS(SharedHandles);
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_SRC_SHARED_HANDLES_H__