action_pipe.h revision 49fdf1889b965be25f929eeebc5b60cd40b9043 
1// Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef UPDATE_ENGINE_PIPE_H__
6#define UPDATE_ENGINE_PIPE_H__
7
8#include <stdio.h>
9#include <iostream>
10#include <map>
11#include <string>
12#include <tr1/memory>
13#include <glog/logging.h>
14#include "base/basictypes.h"
15
16// The structure of these classes (Action, ActionPipe, ActionProcessor, etc.)
17// is based on the KSAction* classes from the Google Update Engine code at
18// http://code.google.com/p/update-engine/ . The author of this file sends
19// a big thanks to that team for their high quality design, implementation,
20// and documentation.
21
22// This class serves as a temporary holding area for an object passed out
23// from one Action and into another Action. It's templated so that it may
24// contain any type of object that an Action outputs/inputs. Actions
25// cannot be bonded (i.e., connected with a pipe) if their output/input
26// object types differ (a compiler error will result).
27//
28// An ActionPipe is generally created with the Bond() method and owned by
29// the two Action objects. a shared_ptr is used so that when the last Action
30// pointing to an ActionPipe dies, the ActionPipe dies, too.
31
32using std::map;
33using std::string;
34using std::tr1::shared_ptr;
35
36namespace chromeos_update_engine {
37
38// Used by Actions an InputObjectType or OutputObjectType to specify that
39// for that type, no object is taken/given.
40class NoneType {};
41
42template<typename T>
43class Action;
44
45template<typename ObjectType>
46class ActionPipe {
47 public:
48  virtual ~ActionPipe() {
49    LOG(INFO) << "ActionPipe died";
50  }
51
52  // This should be called by an Action on its input pipe.
53  // Returns a reference to the stored object.
54  const ObjectType& contents() const { return contents_; }
55
56  // This should be called by an Action on its output pipe.
57  // Stores a copy of the passed object in this pipe.
58  void set_contents(const ObjectType& contents) { contents_ = contents; }
59
60  // Bonds two Actions together with a new ActionPipe. The ActionPipe is
61  // jointly owned by the two Actions and will be automatically destroyed
62  // when the last Action is destroyed.
63  template<typename FromAction, typename ToAction>
64  static void Bond(FromAction* from, ToAction* to) {
65    shared_ptr<ActionPipe<ObjectType> > pipe(new ActionPipe<ObjectType>);
66    from->set_out_pipe(pipe);
67
68    to->set_in_pipe(pipe);  // If you get an error on this line, then
69    // it most likely means that the From object's OutputObjectType is
70    // different from the To object's InputObjectType.
71  }
72
73 private:
74  ObjectType contents_;
75
76  // The ctor is private. This is because this class should construct itself
77  // via the static Bond() method.
78  ActionPipe() {}
79  DISALLOW_COPY_AND_ASSIGN(ActionPipe);
80};
81
82// Utility function
83template<typename FromAction, typename ToAction>
84void BondActions(FromAction* from, ToAction* to) {
85  // TODO(adlr): find something like this that the compiler accepts:
86  // COMPILE_ASSERT(typeof(typename FromAction::OutputObjectType) ==
87  //                typeof(typename ToAction::InputObjectType),
88  //     FromAction_OutputObjectType_doesnt_match_ToAction_InputObjectType);
89  ActionPipe<typename FromAction::OutputObjectType>::Bond(from, to);
90}
91
92}  // namespace chromeos_update_engine
93
94#endif  // UPDATE_ENGINE_PIPE_H__
95