在update_engine-整體結構(二）中分析到了Action，那么我們接着繼續分析.
首先來看一下BuildUpdateActons(...)這個方法。
src/system/update_engine/update_attempter_android.cc
1 void UpdateAttempterAndroid::BuildUpdateActions(const string& url) { 2 CHECK(!processor_->IsRunning()); 3 processor_->set_delegate(this); 4
5 // Actions:
6 shared_ptr<InstallPlanAction> install_plan_action( 7 new InstallPlanAction(install_plan_)); 8
9 HttpFetcher* download_fetcher = nullptr; 10 if (FileFetcher::SupportedUrl(url)) { 11 DLOG(INFO) << "Using FileFetcher for file URL."; 12 download_fetcher = new FileFetcher(); 13 } else { 14 #ifdef _UE_SIDELOAD 15 LOG(FATAL) << "Unsupported sideload URI: " << url; 16 #else
17 LibcurlHttpFetcher* libcurl_fetcher =
18 new LibcurlHttpFetcher(&proxy_resolver_, hardware_); 19 libcurl_fetcher->set_server_to_check(ServerToCheck::kDownload); 20 download_fetcher = libcurl_fetcher; 21 #endif // _UE_SIDELOAD
22 } 23 shared_ptr<DownloadAction> download_action( 24 new DownloadAction(prefs_, 25 boot_control_, 26 hardware_, 27 nullptr, // system_state, not used.
28 download_fetcher)); // passes ownership
29 shared_ptr<FilesystemVerifierAction> filesystem_verifier_action( 30 new FilesystemVerifierAction()); 31
32 shared_ptr<PostinstallRunnerAction> postinstall_runner_action( 33 new PostinstallRunnerAction(boot_control_, hardware_)); 34
35 download_action->set_delegate(this); 36 download_action->set_base_offset(base_offset_); 37 download_action_ = download_action; 38 postinstall_runner_action->set_delegate(this); 39
40 actions_.push_back(shared_ptr<AbstractAction>(install_plan_action)); 41 actions_.push_back(shared_ptr<AbstractAction>(download_action)); 42 actions_.push_back(shared_ptr<AbstractAction>(filesystem_verifier_action)); 43 actions_.push_back(shared_ptr<AbstractAction>(postinstall_runner_action)); 44
45 // Bond them together. We have to use the leaf-types when calling
46 // BondActions().
47 BondActions(install_plan_action.get(), download_action.get()); 48 BondActions(download_action.get(), filesystem_verifier_action.get()); 49 BondActions(filesystem_verifier_action.get(), 50 postinstall_runner_action.get()); 51
52 // Enqueue the actions.
53 for (const shared_ptr<AbstractAction>& action : actions_) 54 processor_->EnqueueAction(action.get()); 55 }
我們會發現processor_,InstallPlanAction,DownloadAction,FilesystemVerifierAction,PostinstallRunnerAction。首先分析processor_,它是在UpdateAttempterAndroid的構造方法中被賦值
1 UpdateAttempterAndroid::UpdateAttempterAndroid( 2 DaemonStateInterface* daemon_state, 3 PrefsInterface* prefs, 4 BootControlInterface* boot_control, 5 HardwareInterface* hardware) 6 : daemon_state_(daemon_state), 7 prefs_(prefs), 8 boot_control_(boot_control), 9 hardware_(hardware), 10 processor_(new ActionProcessor()) { 11 network_selector_ = network::CreateNetworkSelector(); 12 }
ActionProcessor的數據結構為：
1 // An ActionProcessor keeps a queue of Actions and processes them in order.
2
3 namespace chromeos_update_engine { 4
5 class AbstractAction; 6 class ActionProcessorDelegate; 7
8 class ActionProcessor { 9 public: 10 ActionProcessor() = default; 11
12 virtual ~ActionProcessor(); 13
14 // Starts processing the first Action in the queue. If there's a delegate,
15 // when all processing is complete, ProcessingDone() will be called on the
16 // delegate.
17 virtual void StartProcessing(); 18
19 // Aborts processing. If an Action is running, it will have
20 // TerminateProcessing() called on it. The Action that was running and all the
21 // remaining actions will be lost and must be re-enqueued if this Processor is
22 // to use it.
23 void StopProcessing(); 24
25 // Suspend the processing. If an Action is running, it will have the
26 // SuspendProcessing() called on it, and it should suspend operations until
27 // ResumeProcessing() is called on this class to continue. While suspended,
28 // no new actions will be started. Calling SuspendProcessing while the
29 // processing is suspended or not running this method performs no action.
30 void SuspendProcessing(); 31
32 // Resume the suspended processing. If the ActionProcessor is not suspended
33 // or not running in the first place this method performs no action.
34 void ResumeProcessing(); 35
36 // Returns true iff the processing was started but not yet completed nor
37 // stopped.
38 bool IsRunning() const { return current_action_ != nullptr || suspended_; } 39
40 // Adds another Action to the end of the queue.
41 virtual void EnqueueAction(AbstractAction* action); 42
43 // Sets/gets the current delegate. Set to null to remove a delegate.
44 ActionProcessorDelegate* delegate() const { return delegate_; } 45 void set_delegate(ActionProcessorDelegate *delegate) { 46 delegate_ = delegate; 47 } 48
49 // Returns a pointer to the current Action that's processing.
50 AbstractAction* current_action() const { 51 return current_action_; 52 } 53
54 // Called by an action to notify processor that it's done. Caller passes self.
55 void ActionComplete(AbstractAction* actionptr, ErrorCode code); 56
57 private: 58 // Continue processing actions (if any) after the last action terminated with
59 // the passed error code. If there are no more actions to process, the
60 // processing will terminate.
61 void StartNextActionOrFinish(ErrorCode code); 62
63 // Actions that have not yet begun processing, in the order in which
64 // they'll be processed.
65 std::deque<AbstractAction*> actions_; 66
67 // A pointer to the currently processing Action, if any.
68 AbstractAction* current_action_{nullptr}; 69
70 // The ErrorCode reported by an action that was suspended but finished while
71 // being suspended. This error code is stored here to be reported back to the
72 // delegate once the processor is resumed.
73 ErrorCode suspended_error_code_{ErrorCode::kSuccess}; 74
75 // Whether the action processor is or should be suspended.
76 bool suspended_{false}; 77
78 // A pointer to the delegate, or null if none.
79 ActionProcessorDelegate* delegate_{nullptr}; 80
81 DISALLOW_COPY_AND_ASSIGN(ActionProcessor); 82 }; 83
84 // A delegate object can be used to be notified of events that happen
85 // in an ActionProcessor. An instance of this class can be passed to an
86 // ActionProcessor to register itself.
87 class ActionProcessorDelegate { 88 public: 89 virtual ~ActionProcessorDelegate() = default; 90
91 // Called when all processing in an ActionProcessor has completed. A pointer
92 // to the ActionProcessor is passed. |code| is set to the exit code of the
93 // last completed action.
94 virtual void ProcessingDone(const ActionProcessor* processor, 95 ErrorCode code) {} 96
97 // Called when processing has stopped. Does not mean that all Actions have
98 // completed. If/when all Actions complete, ProcessingDone() will be called.
99 virtual void ProcessingStopped(const ActionProcessor* processor) {} 100
101 // Called whenever an action has finished processing, either successfully
102 // or otherwise.
103 virtual void ActionCompleted(ActionProcessor* processor, 104 AbstractAction* action, 105 ErrorCode code) {} 106 }; 107
108 }
從中可以看到ActionProcessor其實就是用來管理Action的，它的方法都比較簡單，根據注釋我們大體就能夠明白每個方法的意思，在遇到的時候某一個方法再具體分析。接下來再看Action它所存在的繼承關系如下
Aciton繼承關系
FilesystemVerifierAction,PostinstallRunnerAction,DownloadAction都繼承了InstallPlanAction,根據繼承關系可以看出他們都會有PerformAction,ActionCompleted等方法。PerformAction()是在Action開始執行前進行調用，而ActionCompleted是在執行完成后進行調用。先來看看InstallPlanAction中的內容
src/system/update_engine/payload_consumer/install_plan.h
1 class InstallPlanAction : public Action<InstallPlanAction> { 2 public: 3 InstallPlanAction() {} 4 explicit InstallPlanAction(const InstallPlan& install_plan): 5 install_plan_(install_plan) {} 6
7 void PerformAction() override { 8 if (HasOutputPipe()) { 9 SetOutputObject(install_plan_); 10 } 11 processor_->ActionComplete(this, ErrorCode::kSuccess); 12 } 13
14 InstallPlan* install_plan() { return &install_plan_; } 15
16 static std::string StaticType() { return "InstallPlanAction"; } 17 std::string Type() const override { return StaticType(); } 18
19 typedef ActionTraits<InstallPlanAction>::InputObjectType InputObjectType; 20 typedef ActionTraits<InstallPlanAction>::OutputObjectType OutputObjectType; 21
22 private: 23 InstallPlan install_plan_; 24
25 DISALLOW_COPY_AND_ASSIGN(InstallPlanAction); 26 };
可以看到InstallAction比較簡單，僅僅是將install_plan_設置為了輸出對象，傳遞給了下一個Action,這是Action之間的一個通信方式，這個方式可以稱之為pipe方式，下面來分析一下這種通信方式。先來看在Action這個類里面提到的ActionPipe
src/system/update_engine/common/action_pipe.h
1 namespace chromeos_update_engine { 2
3 // Used by Actions an InputObjectType or OutputObjectType to specify that
4 // for that type, no object is taken/given.
5 class NoneType {}; 6
7 template<typename T>
8 class Action; 9
10 template<typename ObjectType>
11 class ActionPipe { 12 public: 13 virtual ~ActionPipe() {} 14
15 // This should be called by an Action on its input pipe.
16 // Returns a reference to the stored object.
17 const ObjectType& contents() const { return contents_; } //獲取管道中的內容
18
19 // This should be called by an Action on its output pipe.
20 // Stores a copy of the passed object in this pipe.
21 void set_contents(const ObjectType& contents) { contents_ = contents; } //設置管道中的內容
22
23 // Bonds two Actions together with a new ActionPipe. The ActionPipe is
24 // jointly owned by the two Actions and will be automatically destroyed
25 // when the last Action is destroyed.
26 template<typename FromAction, typename ToAction>
27 static void Bond(FromAction* from, ToAction* to) { //將兩個Action連接通過pipe連接在一起
28 std::shared_ptr<ActionPipe<ObjectType>> pipe(new ActionPipe<ObjectType>); 29 from->set_out_pipe(pipe); 30
31 to->set_in_pipe(pipe); // If you get an error on this line, then
32 // it most likely means that the From object's OutputObjectType is
33 // different from the To object's InputObjectType.
34 } 35
36 private: 37 ObjectType contents_; 38
39 // The ctor is private. This is because this class should construct itself
40 // via the static Bond() method.
41 ActionPipe() {} 42 DISALLOW_COPY_AND_ASSIGN(ActionPipe); 43 }; 44
45 // Utility function
46 template<typename FromAction, typename ToAction>
47 void BondActions(FromAction* from, ToAction* to) { 48 static_assert( 49 std::is_same<typename FromAction::OutputObjectType, 50 typename ToAction::InputObjectType>::value, 51 "FromAction::OutputObjectType doesn't match ToAction::InputObjectType"); 52 ActionPipe<typename FromAction::OutputObjectType>::Bond(from, to); 53 } 54
55 }
可以看到ActionPipe主要就是將兩個Action連接在一起。為什么說就會連接在一起呢？再來看Action中相關的方法
src/system/update_engine/common/action.h
1 template<typename SubClass>
2 class Action : public AbstractAction { 3 public: 4 ~Action() override {} 5
6 // Attaches an input pipe to this Action. This is optional; an Action
7 // doesn't need to have an input pipe. The input pipe must be of the type
8 // of object that this class expects.
9 // This is generally called by ActionPipe::Bond()
10 void set_in_pipe( //設置輸入管道
11 // this type is a fancy way of saying: a shared_ptr to an
12 // ActionPipe<InputObjectType>.
13 const std::shared_ptr<ActionPipe<
14 typename ActionTraits<SubClass>::InputObjectType>>& in_pipe) { 15 in_pipe_ = in_pipe; 16 } 17
18 // Attaches an output pipe to this Action. This is optional; an Action
19 // doesn't need to have an output pipe. The output pipe must be of the type
20 // of object that this class expects.
21 // This is generally called by ActionPipe::Bond()
22 void set_out_pipe( //設置輸出管道
23 // this type is a fancy way of saying: a shared_ptr to an
24 // ActionPipe<OutputObjectType>.
25 const std::shared_ptr<ActionPipe<
26 typename ActionTraits<SubClass>::OutputObjectType>>& out_pipe) { 27 out_pipe_ = out_pipe; 28 } 29
30 // Returns true iff there is an associated input pipe. If there's an input
31 // pipe, there's an input object, but it may have been constructed with the
32 // default ctor if the previous action didn't call SetOutputObject().
33 bool HasInputObject() const { return in_pipe_.get(); } //是否有輸入管道
34
35 // returns a const reference to the object in the input pipe.
36 const typename ActionTraits<SubClass>::InputObjectType& GetInputObject() //獲取輸入的內容
37 const { 38 CHECK(HasInputObject()); 39 return in_pipe_->contents(); 40 } 41
42 // Returns true iff there's an output pipe.
43 bool HasOutputPipe() const { //是否有輸出管道
44 return out_pipe_.get(); 45 } 46
47 // Copies the object passed into the output pipe. It will be accessible to
48 // the next Action via that action's input pipe (which is the same as this
49 // Action's output pipe).
50 void SetOutputObject( //設置輸出的內容
51 const typename ActionTraits<SubClass>::OutputObjectType& out_obj) { 52 CHECK(HasOutputPipe()); 53 out_pipe_->set_contents(out_obj); 54 } 55
56 // Returns a reference to the object sitting in the output pipe.
57 const typename ActionTraits<SubClass>::OutputObjectType& GetOutputObject() { //獲取輸出的內容
58 CHECK(HasOutputPipe()); 59 return out_pipe_->contents(); 60 } 61
62 protected: 63 // We use a shared_ptr to the pipe. shared_ptr objects destroy what they
64 // point to when the last such shared_ptr object dies. We consider the
65 // Actions on either end of a pipe to "own" the pipe. When the last Action
66 // of the two dies, the ActionPipe will die, too.
67 std::shared_ptr<ActionPipe<typename ActionTraits<SubClass>::InputObjectType>>
68 in_pipe_; 69 std::shared_ptr<ActionPipe<typename ActionTraits<SubClass>::OutputObjectType>>
70 out_pipe_; 71 };
從這里我們就能夠看出每個Action其實有兩個ActionPipe，一個是輸入ActionPipe，一個是輸出ActionPipe，輸入ActionPipe和前一個Action的輸出ActionPipe其實是一個ActionPipe,輸出Actionpipe和下一個Action的輸出ActionPipe是一個ActionPipe.
ActionTraits在這個類里僅僅是為InstallPlan這個類型定義了一個新的類型
src/system/update_engine/payload_consumer/install_plan.h
1 template<>
2 class ActionTraits<InstallPlanAction> { 3 public: 4 // Takes the install plan as input
5 typedef InstallPlan InputObjectType; 6 // Passes the install plan as output
7 typedef InstallPlan OutputObjectType; 8 };
到這里Action機制也分析的差不多了，我們可以回到BuildUpdateActions中繼續進行分析了。
1 void UpdateAttempterAndroid::BuildUpdateActions(const string& url) { 2 CHECK(!processor_->IsRunning()); 3 processor_->set_delegate(this); 4 5 // Actions: 6 shared_ptr<InstallPlanAction> install_plan_action( 7 new InstallPlanAction(install_plan_)); 8 9 HttpFetcher* download_fetcher = nullptr; 10 if (FileFetcher::SupportedUrl(url)) { 11 DLOG(INFO) << "Using FileFetcher for file URL."; 12 download_fetcher = new FileFetcher(); 13 } else { 14 #ifdef _UE_SIDELOAD 15 LOG(FATAL) << "Unsupported sideload URI: " << url; 16 #else 17 LibcurlHttpFetcher* libcurl_fetcher = 18 new LibcurlHttpFetcher(&proxy_resolver_, hardware_); 19 libcurl_fetcher->set_server_to_check(ServerToCheck::kDownload); 20 download_fetcher = libcurl_fetcher; 21 #endif // _UE_SIDELOAD 22 } 23 shared_ptr<DownloadAction> download_action( 24 new DownloadAction(prefs_, 25 boot_control_, 26 hardware_, 27 nullptr, // system_state, not used. 28 download_fetcher)); // passes ownership 29 shared_ptr<FilesystemVerifierAction> filesystem_verifier_action( 30 new FilesystemVerifierAction()); 31 32 shared_ptr<PostinstallRunnerAction> postinstall_runner_action( 33 new PostinstallRunnerAction(boot_control_, hardware_)); 34 35 download_action->set_delegate(this); 36 download_action->set_base_offset(base_offset_); 37 download_action_ = download_action; 38 postinstall_runner_action->set_delegate(this); 39 40 actions_.push_back(shared_ptr<AbstractAction>(install_plan_action)); 41 actions_.push_back(shared_ptr<AbstractAction>(download_action)); 42 actions_.push_back(shared_ptr<AbstractAction>(filesystem_verifier_action)); 43 actions_.push_back(shared_ptr<AbstractAction>(postinstall_runner_action)); 44 45 // Bond them together. We have to use the leaf-types when calling 46 // BondActions(). 47 BondActions(install_plan_action.get(), download_action.get()); 48 BondActions(download_action.get(), filesystem_verifier_action.get()); 49 BondActions(filesystem_verifier_action.get(), 50 postinstall_runner_action.get()); 51 52 // Enqueue the actions. 53 for (const shared_ptr<AbstractAction>& action : actions_) 54 processor_->EnqueueAction(action.get()); 55 }
在這個方法里主要做了：
1.為processor_設置delegate,其實也就是注冊了回調方法，UpdateAttempterAndroid實現了ActionProcessDelegate中的方法.
2. 創建了InstallPlanAction
3.創建了download_fetcher，我們這里假定用的是本地的文件既使用file:///協議，所以download_fetcher即為FileFetcher,從這一部分的代碼可以看HtppFetcher,FileFetcher,LibcurlHttpFetcher之間具有繼承或實現的關系。
4.創建DownloadAction,注意在創建的時候傳入了download_fetcher為FileFetcher類型
5.創建FilesystemVerifierAction，PostinstallRunnerAction.從這里可以看出升級流程的精華應該就是這三個Action了
6.為download_action設置delegate，設置開始下載的offfset等，因為代碼中設置delegate的操作比較多，如果不注意很有可能記混亂了。
7.為postinstall_runner_action設置delegate
8.將Action加入到Action的集合中
9.使用BondActions方法為Action之間建立管道。
10.將action遍歷放入到processor_的隊列中，並且設置action的管理者為processor_。
在分析完這個方法所干的事情之后，再分析一下HtppFetcher,FileFetcher,LibcurlHttpFetcher這三者之間的關系
HtppFetcher,FileFetcher,LibcurlHttpFetcher這三者之間的關系
現在繼續分析ApplyPayload中的最后一個方法UpdateBootFlags()
1 void UpdateAttempterAndroid::UpdateBootFlags() { 2 if (updated_boot_flags_) { 3 LOG(INFO) << "Already updated boot flags. Skipping."; 4 CompleteUpdateBootFlags(true); 5 return; 6 } 7 // This is purely best effort.
8 LOG(INFO) << "Marking booted slot as good."; 9 if (!boot_control_->MarkBootSuccessfulAsync( 10 Bind(&UpdateAttempterAndroid::CompleteUpdateBootFlags, 11 base::Unretained(this)))) { 12 LOG(ERROR) << "Failed to mark current boot as successful."; 13 CompleteUpdateBootFlags(false); 14 } 15 }
首先檢查當前運行的slot是否已經被標記為successful狀態，如果是則調用CompleteUpdateBootFlags方法，否則的就調用MarkBootSuccessfulAsync將當前的slot標記為successful。標記完成后調用CompleteUpdateBootFlags方法
1 void UpdateAttempterAndroid::CompleteUpdateBootFlags(bool successful) { 2 updated_boot_flags_ = true; 3 ScheduleProcessingStart(); 4 }
從這里看出即使標記失敗了仍然調用 ScheduleProcessingStart()，這個方法主要就是開始執行Action
1 void UpdateAttempterAndroid::ScheduleProcessingStart() { 2 LOG(INFO) << "Scheduling an action processor start."; 3 brillo::MessageLoop::current()->PostTask( 4 FROM_HERE, 5 Bind([](ActionProcessor* processor) { processor->StartProcessing(); }, 6 base::Unretained(processor_.get()))); 7 }
在來看看StartProcessing()方法的實現，首先是獲取對列中的第一個action,打印action的類型，之后將action移出隊列，並且調用PerformAction。
src/system/update_engine/common/action_processor.cc
1 void ActionProcessor::StartProcessing() { 2 CHECK(!IsRunning()); 3 if (!actions_.empty()) { 4 current_action_ = actions_.front(); 5 LOG(INFO) << "ActionProcessor: starting " << current_action_->Type(); 6 actions_.pop_front(); 7 current_action_->PerformAction(); 8 } 9 }
分析到了這里就對整體的update_engine有了一定的了解，接下來只需要對各個Action逐個擊破就好了。在之前已經看過了InstallPlanAction，它的內容很簡單，僅僅是在輸出管道中設置了install_plan_,接下來就調用了processor_->ActionComplete(this, ErrorCode::kSuccess),看一下ActionComplete的內容，它是如何讓下一個action開始執行的。
1 void ActionProcessor::ActionComplete(AbstractAction* actionptr, 2 ErrorCode code) { 3 CHECK_EQ(actionptr, current_action_); 4 if (delegate_) 5 delegate_->ActionCompleted(this, actionptr, code); 6 string old_type = current_action_->Type(); 7 current_action_->ActionCompleted(code); 8 current_action_->SetProcessor(nullptr); 9 current_action_ = nullptr; 10 LOG(INFO) << "ActionProcessor: finished "
11 << (actions_.empty() ? "last action " : "") << old_type 12 << (suspended_ ? " while suspended" : "") 13 << " with code " << utils::ErrorCodeToString(code); 14 if (!actions_.empty() && code != ErrorCode::kSuccess) { 15 LOG(INFO) << "ActionProcessor: Aborting processing due to failure."; 16 actions_.clear(); 17 } 18 if (suspended_) { 19 // If an action finished while suspended we don't start the next action (or
20 // terminate the processing) until the processor is resumed. This condition
21 // will be flagged by a nullptr current_action_ while suspended_ is true.
22 suspended_error_code_ = code; 23 return; 24 } 25 StartNextActionOrFinish(code); 26 }
其實這個方法中也就進行了善后和開始下一個Action的工作。包括:
1.判斷是否注冊了回調方法。這里的delegate_的類型為UpdateAttempterAndroid。如果注冊了就回調ActionCompleted方法，在UpdateAttempterAndroid中它的內容為
1 void UpdateAttempterAndroid::ActionCompleted(ActionProcessor* processor, 2 AbstractAction* action, 3 ErrorCode code) { 4 // Reset download progress regardless of whether or not the download
5 // action succeeded.
6 const string type = action->Type(); 7 if (type == DownloadAction::StaticType()) { 8 download_progress_ = 0; 9 } 10 if (code != ErrorCode::kSuccess) { 11 // If an action failed, the ActionProcessor will cancel the whole thing.
12 return; 13 } 14 if (type == DownloadAction::StaticType()) { 15 SetStatusAndNotify(UpdateStatus::FINALIZING); 16 } 17 }
可以看到這個方法主要就是為重置下載的進度。
2.調用當前的Action的ActionCompleted，將Processor和當前Action置空等。
3.如果執行到某人Action的時候出了錯，則停止執行其他的Action
4. processor如果被掛起，則暫停執行下一個Action
5.執行下一個Action或者是否完成了所有的Action,StartNextActionOrFinish(code),該方法比較簡單，就不進行分析了。
到這里整體的Action的執行流程也就通了,下一篇開始會分析其他三個Action
.