SMC状态机 讲解1 XX.sm文件详解

SMC状态机 讲解1.4 XX.sm文件

• 1、Task类
• 2、FSM任务
• 3、创建SMC.sm文件
• 4、定义FSM状态
• 5、定义转换 transition
• 6、定义FSM转换动作
• 7、定义FSM默认转换
• 8、定义状态Entry/Exit 动作
• 9、连接Task与Task FSM

1、Task类

SMC为对象(不是进程或应用程序，而是单个对象)生成有限状态机。如果有接收异步回调的对象，并且对象响应这些回调是基于对象状态的，那么SMC提供了一个强大的解决方案。

package com.acme.supercron;public final class Task implements TaskEventListener,TimerEventListener
{public Task(){// 对象初始化...}//-----------------------------------------------------------// TaskEventListener Interface Implemenation.//// 未完成任务在指定时间片内继续工作的时间。public void start(long timeSlice){...}// 当一个正在运行的、未完成的任务应该暂停运行时调用，即使它的时间片没有过期。// 注意:当时间片过期时，任务的运行也会暂停。public void suspend(){...}// 当未完成的任务被阻塞时调用。被阻塞的任务在解除阻塞后能够继续运行。public void block(){...}// 当阻塞的任务被解除阻塞并允许继续运行时调用。public void unblock(){...}// 当一个未完成的任务被永久停止时调用。// 然后删除已停止的任务。public void stop(){...}// 当任务被删除时调用。出现以下情况之一调用：//1.任务已经完成运行并且现在被停止//2.系统正在关闭并且所有任务都将立即终止时，任务将被删除。public void delete(){...}//// end of TaskEventListener Interface Implemenation.//-----------------------------------------------------------//-----------------------------------------------------------// TimerEventListener Interface Implementation.//// 当时间片计时器到期时调用。如果运行，任务挂起。public void handleTimeout(TimerEvent event){...}//// end of TimerEventListener Interface Implementation.//-----------------------------------------------------------// Remainder of class definition....
}

2、FSM任务

任务FSM示意图如下:
任务的状态是:

1. Running:任务正在运行。允许任务在指定的时间限制内运行。
2. Suspended:任务尚未完成，正在等待再次运行。
3. Stopped:任务已完成运行或外部停止。
4. Blocked:未完成的任务被外部阻止再次运行。它将保持这种状态，直到停止或解除阻塞。
5. Stopping:任务在进入停止状态前，正在清理已分配的资源。
6. Deleted:任务完全停止，关联资源全部返回。现在可以安全地删除任务了。FSM的结束状态。

3、创建SMC.sm文件

XX.sm 文件是一个没有定义状态或转换的框架。包含以下特性:

代码实现：

%{
//编写注释
//...
%}// This FSM works for the Task class only and only the Task
// class may instantiate it.%class Task
%package com.acme.supercron
%fsmclass TaskFSM
%fsmfile TaskFSM
%access package// A %map name cannot be the same as the FSM class name.
%start TaskMap::Suspended
%map TaskMap
%%...
%%

4、定义FSM状态

在%map TaskFSM %% … %% 分隔符中定义FSM状态

// 此FSM只对Task类起作用
// class可以实例化.
%class Task
%package com.acme.supercron
%fsmclass TaskFSM
%fsmfile TaskFSM
%access package// %map 名字不能与FSM类名相同
%start TaskMap::Suspended
%map TaskMap
%%
Suspended
{...
}
Running
{...
}
// 此处等待解锁、停止、删除
Blocked
{...
}Stopping
{...
}
Stopped
{...
}
Deleted
{...
}
...
%%

5、定义转换 transition

转换由四个部分组成:

1. transition name:转换名称
2. transition guard:转换保护（可选）
3. 转换结束时的状态
4. transition action:转换动作

下面介绍Stop、Block和Delete转换：

// 该FSM只对Task类工作，并且只对Task类工作
// 类可以实例化
%class Task
%package com.acme.supercron
%package package
%fsmclass TaskFSM
%fsmfile TaskFSM
%access package// %map名称不能与FSM的类名相同
%start TaskMap::Suspended
%map TaskMap
%%
Suspended
{// Time to do more work.// 时间片持续时间作为转换传入// argument.Start(timeslice: long) // 转换名称Running // 转换结束后的状态{... // 执行动作}
}Running
{// 等待时间片Suspend //转换名称Suspended //转换结束后的状态{...}// Task已经完成.DoneStopped{...}
}// 等待解锁、停止或删除
Blocked
{// The task may continue working now.UnblockSuspended{...}
}
Stopping
{// task结束StoppedStopped{...}
}
Stopped
{...
}
Deleted
{...
}...
%%

6、定义FSM转换动作

转换操作是FSM和应用程序类Task之间的第一次耦合。actions是Task的方法。这些方法必须具有以下属性:

1. FSM可访问，这意味着至少有public方法。或者如果在同一个package中，则有package方法。
2. 有void返回类型。如果该方法确实返回值，则FSM将忽略该值。

SMC对转换参数没有语法限制，只是将它们用“()”括号括起来并以逗号分隔。

// This FSM works for the Task class only and only the Task
// class may instantiate it.
%class Task
%package com.acme.supercron
%fsmclass TaskFSM
%fsmfile TaskFSM
%access package// A %map name cannot be the same as the FSM class name.
%start TaskMap::Suspended
%map TaskMap
%%
Suspended
{// Time to do more work.// The timeslice duration is passed in as a transition// argument.Start(timeslice: long)Running{continueTask();startSliceTimer(timeslice);}
}Running
{// Wait for another time slice.SuspendSuspended{stopSliceTimer();suspendTask();}// Task has completed.DoneStopped{stopSliceTimer();releaseResources();}
}// Wait here to be either unblocked, stopped or deleted.
Blocked
{// The task may continue working now.// No actions needed.UnblockSuspended{}
}Stopping
{// The task is now stopped.StoppedStopped{releaseResources();}
}Stopped
{...
}Deleted
{...
}
...
%%

Task中的转换动作方法为:

package com.acme.supercron;public final class Task implements TaskEventListener, TimerEventListener
{public Task(){// 对象初始化...}//-----------------------------------------------------------// TaskEventListener Interface Implemenation.//<snip>//// end of TaskEventListener Interface Implemenation.//-----------------------------------------------------------//-----------------------------------------------------------// TimerEventListener Interface Implementation.//<snip>//// end of TimerEventListener Interface Implementation.//-----------------------------------------------------------//-----------------------------------------------------------// State Machine Actions.//// Activate the underlying task and get it running again./* package */ void continueTask(){...return;}// Inactivate the underlying task./* package */ void suspendTask(){...return;}// Start the timeslice timer for the given milliseconds./* package */ void startSliceTimer(long timeslice){...return;}// Stop the timeslice timer./* package */ void stopSliceTimer(){...return;}// Return system resources from whence they came./* package */ void releaseResources(){...return;}//// end of State Machine Actions.//-----------------------------------------------------------// Remainder of class definition....
}

7、定义FSM默认转换

现在已经定义了转换“Stop”、“Block”和“Delete”。这些转换没有开始状态的原因是，无论当前状态如何，都要进行转换。

1. Stop:如果task仍然是alive的(处于Suspended、Running或Blocked状态)，那么它必须立即转换到stop状态。如果任务为not alive(在其他三种状态下)，则忽略此转换，因为task不再alive。
2. Block:如果task处于Suspended或running状态，那么它将转换到Bolcked状态。否则该请求将被忽略。
3. Delete:如果task处于除Deleted之外的任何状态，那么它必须转换到Deleted状态。

SMC提供了两种定义默认转换的方法:Default状态和Default转换。sm更新了默认的Stop, Block和Delete转换定义:

// This FSM works for the Task class only and only the Task
// class may instantiate it.
%class Task
%package com.acme.supercron
%fsmclass TaskFSM
%fsmfile TaskFSM
%access package// A %map name cannot be the same as the FSM class name.
%start TaskMap::Suspended
%map TaskMap
%%
Suspended
{// Time to do more work.// The timeslice duration is passed in as a transition// argument.Start(timeslice: long)Running{continueTask();startSliceTimer(timeslice);}BlockBlocked{blockTask();}Running
{// Wait for another time slice.SuspendSuspended{stopSliceTimer();suspendTask();}BlockBlocked{stopSliceTimer();blockTask();}// Task has completed.DoneStopped{stopSliceTimer();releaseResources();}
}// Wait here to be either unblocked, stopped or deleted.
Blocked
{// The task may continue working now.// No actions needed.UnblockSuspended{}
}Stopping
{// The task is now stopped.StoppedStopped{releaseResources();}// We are stopping.Stopnil{}
}Stopped
{// We are stopping.Stopnil{}// Ignore all transitions until deleted.Defaultnil{}
}Deleted
{// Define all known transitions as loopbacks.Start(timeslice: long)nil{}Suspend()nil{}Block()nil{}Unblock()nil{}Done()nil{}Stop()nil{}Stopped()nil{}Delete()nil{}
}Default
{// Three states follow this transition, three states ignore.// So define the active definition.StopStopping{stopTask();}// Block is ignored by four of six states.// Force the other two states to define this.// Note the "nil" end state. This is a loopback transitionBlocknil{}// All but the Delete state follow this transition. Define it here.DeleteDeleted{}// Ignore a transition by default.Defaultnil{}
}
%%

blockTask()和stopTask()方法被添加到Task类中:

package com.acme.supercron;public final class Task implements TaskEventListener, TimerEventListener
{public Task(){// Object initialization....}<snip>//-----------------------------------------------------------// State Machine Actions.//<snip>// Block the underlying task from running./* package */ void blockTask(){...return;}// Permanently stop the underlying task./* package */ void stopTask(){...return;}<snip>//// end of State Machine Actions.//-----------------------------------------------------------// Remainder of class definition....
}

8、定义状态Entry/Exit 动作

当不处于Running状态时，应该停止时间片定时器。实现这一点的方法是在Running中添加一个Exit块，并将stopSliceTimer()动作移动到那里。

由于正在定义状态的Exit动作，因此将startSliceTimer()动作放入Entry块中似乎是很自然的。但反对的理由有两点:

1. 进入运行状态的转换只有一次。将startSliceTimer()从Suspended的Start过渡移动到Running的entry动作没有任何好处。
2. startSliceTimer()接受Start转换的时间片参数。如果startSliceTimer()是一个入口操作，那么它不能访问转换参数。解决这个问题的唯一方法是将切片时间存储在Task类中，然后在entry动作(startSliceTimer(ctext . getslicetime()))中立即检索它。现在，将动作移动到entry块比什么都不做还要糟糕。

// This FSM works for the Task class only and only the Task
// class may instantiate it.
%class Task
%package com.acme.supercron
%fsmclass TaskFSM
%fsmfile TaskFSM
%access package// A %map name cannot be the same as the FSM class name.
%start TaskMap::Suspended
%map TaskMap
%%
RunningExit{stopSliceTimer();}
{// Wait for another time slice.SuspendSuspended{// stopSliceTimer(); moved.suspendTask();}BlockBlocked{// stopSliceTimer(); moved.blockTask();}// Task has completed.DoneStopped{// stopSliceTimer(); moved.releaseResources();}
}

}
%%

9、连接Task与Task FSM

将FSMs连接到它们的应用程序类非常简单:

1. 在Task类中添加数据成员TaskFSM _fsm
2. 在Task的构造函数中实例化TaskFSM。
3. 如果start状态有必须在创建FSM时执行的entry动作，那么在Task的构造函数之外调用_fsm.enterStartState()
4. 当你需要发出一个转换时，调用_fsm相应的转换方法:

_fsm.Start(timeSlice);

package com.acme.supercron;public final class Taskimplements TaskEventListener,TimerEventListener
{public Task(){// Object initialization....// Instantiate the FSM here but perform the initial// state's entry actions outside of the constructor// to prevent referencing this object before its// initialization is complete._fsm = new TaskFSM(this);}// Execute the start state's entry actions by calling this// method. This method should be called only once and prior to// issuing any transitions. Therefore this method should be// called before registering this Task instance as a task and// timer event listener.public void startFSM(){_fsm.enterStartState();TaskManager.addListener(this);}//-----------------------------------------------------------// TaskEventListener Interface Implemenation.//// Time for the incomplete task to continue its work for the// specified time slice.public void start(long timeSlice){_fsm.Start(timeSlice);}// Called when a running, incomplete task should suspend// running even though its time slice is not expired.// Note: the task's running is also suspended when the time// slice expires.public void suspend(){_fsm.Suspend();}// Called when an incomplete task is blocked. Blocked tasks// are able to continue running when unblocked.public void block(){_fsm.Block();}// Called when a blocked task is unblocked and allowed// to continue running.public void unblock(){_fsm.Unblock();}// Called when an incomplete task is permanently stopped.// Stopped tasks are then deleted.public void stop(){_fsm.Stop();}// Called when the task is deleted. Tasks are deleted when// either 1) the task has completed running and is now// stopped or 2) when the system is shutting down and all// are to terminate immediately.public void delete(){_fsm.Delete();}//// end of TaskEventListener Interface Implemenation.//-----------------------------------------------------------//-----------------------------------------------------------// TimerEventListener Interface Implementation.//// Called with the time slice timer has expired. If running,// the task is suspended.public void handleTimeout(TimerEvent event){_fsm.Suspend();}//// end of TimerEventListener Interface Implementation.//-----------------------------------------------------------<snip>// The associated finite state machine.private final TaskFSM _fsm;
}

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