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git-svn-id: svn://chrome-svn/chromeos/trunk@24 06c00378-0e64-4dae-be16-12b19f9950a1
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+// Copyright (c) 2009 The Chromium OS 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 UPDATE_ENGINE_PIPE_H__
+#define UPDATE_ENGINE_PIPE_H__
+
+#include <stdio.h>
+#include <iostream>
+#include <map>
+#include <string>
+#include <tr1/memory>
+#include <glog/logging.h>
+#include "base/basictypes.h"
+
+// The structure of these classes (Action, ActionPipe, ActionProcessor, etc.)
+// is based on the KSAction* classes from the Google Update Engine code at
+// http://code.google.com/p/update-engine/ . The author of this file sends
+// a big thanks to that team for their high quality design, implementation,
+// and documentation.
+
+// This class serves as a temporary holding area for an object passed out
+// from one Action and into another Action. It's templated so that it may
+// contain any type of object that an Action outputs/inputs. Actions
+// cannot be bonded (i.e., connected with a pipe) if their output/input
+// object types differ (a compiler error will result).
+//
+// An ActionPipe is generally created with the Bond() method and owned by
+// the two Action objects. a shared_ptr is used so that when the last Action
+// pointing to an ActionPipe dies, the ActionPipe dies, too.
+
+using std::map;
+using std::string;
+using std::tr1::shared_ptr;
+
+namespace chromeos_update_engine {
+
+// Used by Actions an InputObjectType or OutputObjectType to specify that
+// for that type, no object is taken/given.
+class NoneType {};
+
+template<typename T>
+class Action;
+
+template<typename ObjectType>
+class ActionPipe {
+ public:
+ virtual ~ActionPipe() {
+ LOG(INFO) << "ActionPipe died";
+ }
+
+ // This should be called by an Action on its input pipe.
+ // Returns a reference to the stored object.
+ const ObjectType& contents() const { return contents_; }
+
+ // This should be called by an Action on its output pipe.
+ // Stores a copy of the passed object in this pipe.
+ void set_contents(const ObjectType& contents) { contents_ = contents; }
+
+ // Bonds two Actions together with a new ActionPipe. The ActionPipe is
+ // jointly owned by the two Actions and will be automatically destroyed
+ // when the last Action is destroyed.
+ template<typename FromAction, typename ToAction>
+ static void Bond(FromAction* from, ToAction* to) {
+ shared_ptr<ActionPipe<ObjectType> > pipe(new ActionPipe<ObjectType>);
+ from->set_out_pipe(pipe);
+
+ to->set_in_pipe(pipe); // If you get an error on this line, then
+ // it most likely means that the From object's OutputObjectType is
+ // different from the To object's InputObjectType.
+ }
+
+ private:
+ ObjectType contents_;
+
+ // The ctor is private. This is because this class should construct itself
+ // via the static Bond() method.
+ ActionPipe() {}
+ DISALLOW_COPY_AND_ASSIGN(ActionPipe);
+};
+
+// Utility function
+template<typename FromAction, typename ToAction>
+void BondActions(FromAction* from, ToAction* to) {
+ // TODO(adlr): find something like this that the compiler accepts:
+ // COMPILE_ASSERT(typeof(typename FromAction::OutputObjectType) ==
+ // typeof(typename ToAction::InputObjectType),
+ // FromAction_OutputObjectType_doesnt_match_ToAction_InputObjectType);
+ ActionPipe<typename FromAction::OutputObjectType>::Bond(from, to);
+}
+
+} // namespace chromeos_update_engine
+
+#endif // UPDATE_ENGINE_PIPE_H__