android StateMachine.java

android 4.0.4: /frameworks/base/core/java/com/android/internal/util/StateMachine.java

StateMachine状态机中，会创建HandlerThread线程，和依附该线程的Handler；消息处理都是在HandlerThread中执行

framework层的好几个状态机，都是在StateMachine基础上实现的，比如：WifiStateMachine、DhcpStateMachine、WifiWatchdogStateMachine。。。

http://androidxref.com/4.0.4/xref/frameworks/base/core/java/com/android/internal/util/StateMachine.java

SmHandler：

       /**
         * Handle messages sent to the state machine by calling
         * the current state's processMessage. It also handles
         * the enter/exit calls and placing any deferred messages
         * back onto the queue when transitioning to a new state.
         */
        @Override
        public final void handleMessage(Message msg) {
            if (mDbg) Log.d(TAG, "handleMessage: E msg.what=" + msg.what);

            /** Save the current message */
            mMsg = msg;

            /**
             * Check that construction was completed
             */
            if (!mIsConstructionCompleted) {
                Log.e(TAG, "The start method not called, ignore msg: " + msg);//  在状态机没有启动之前，收到msg，只是打印error日志
                return;
            }

            /**
             * Process the message abiding by the hierarchical semantics
             * and perform any requested transitions.
             */
            processMsg(msg);
            performTransitions();

            if (mDbg) Log.d(TAG, "handleMessage: X");
        }

        /**
         * Complete the construction of the state machine.
         */
        private final void completeConstruction() {
            if (mDbg) Log.d(TAG, "completeConstruction: E");

            /**
             * Determine the maximum depth of the state hierarchy
             * so we can allocate the state stacks.
             */
            int maxDepth = 0;
            for (StateInfo si : mStateInfo.values()) {
                int depth = 0;
                for (StateInfo i = si; i != null; depth++) {
                    i = i.parentStateInfo;
                }
                if (maxDepth < depth) {
                    maxDepth = depth;
                }
            }
            if (mDbg) Log.d(TAG, "completeConstruction: maxDepth=" + maxDepth);

            mStateStack = new StateInfo[maxDepth];
            mTempStateStack = new StateInfo[maxDepth];
            setupInitialStateStack();

            /**
             * Construction is complete call all enter methods
             * starting at the first entry.
             */
            mIsConstructionCompleted = true;
            mMsg = obtainMessage(SM_INIT_CMD);
            invokeEnterMethods(0);// 初始状态的enter方法，在调用线程中执行；即如果在UI线程中，调用状态机的start()方法，则初始状态的enter方法，在UI线程中执行，如果enter方法中有耗时的操作，肯定会占用UI线程的资源

            /**
             * Perform any transitions requested by the enter methods
             */
            performTransitions();// 如果初始状态的enter方法中，有跳转，即调用了transitionTo方法，则初始状态的exit方法、新状态的enter方法，也都会在调用线程中执行，依次类推，也会进一步占用调用线程的资源

            if (mDbg) Log.d(TAG, "completeConstruction: X");
        }

StateMachine：

    /**
     * Start the state machine.
     */
    public void start() {
        // mSmHandler can be null if the state machine has quit.
        if (mSmHandler == null) return;

        /** Send the complete construction message */
        mSmHandler.completeConstruction();
    }

///////////////////////////////////////////////////////////////////////////////////////////////////////////     

android 4.1.1: /frameworks/base/core/java/com/android/internal/util/StateMachine.java

http://androidxref.com/4.1.1/xref/frameworks/base/core/java/com/android/internal/util/StateMachine.java

SmHandler：

        /**
         * Handle messages sent to the state machine by calling
         * the current state's processMessage. It also handles
         * the enter/exit calls and placing any deferred messages
         * back onto the queue when transitioning to a new state.
         */
        @Override
        public final void handleMessage(Message msg) {
            if (mDbg) Log.d(TAG, "handleMessage: E msg.what=" + msg.what);

            /** Save the current message */
            mMsg = msg;

            if (mIsConstructionCompleted) {
                /** Normal path */
                processMsg(msg);
            } else if (!mIsConstructionCompleted && (mMsg.what == SM_INIT_CMD) && (mMsg.obj == mSmHandlerObj)) {
                /** Initial one time path. */
                mIsConstructionCompleted = true;// 调用start方法，走该分支一次；后面处理消息，都走前面的分支processMsg；(在HandlerThread线程中执行)
                invokeEnterMethods(0);
            } else {
                throw new RuntimeException("StateMachine.handleMessage: " + "The start method not called, received msg: " + msg);//  这里也是修改点，状态机没有启动之前，即没有调用start()方法之前，在4.0.4上，是打印error日志；在4.1.1上，则是
            }
            performTransitions();

            if (mDbg) Log.d(TAG, "handleMessage: X");
        }

        /**
         * Complete the construction of the state machine.
         */
        private final void completeConstruction() {
            if (mDbg) Log.d(TAG, "completeConstruction: E");

            /**
             * Determine the maximum depth of the state hierarchy
             * so we can allocate the state stacks.
             */
            int maxDepth = 0;
            for (StateInfo si : mStateInfo.values()) {
                int depth = 0;
                for (StateInfo i = si; i != null; depth++) {
                    i = i.parentStateInfo;
                }
                if (maxDepth < depth) {
                    maxDepth = depth;
                }
            }
            if (mDbg) Log.d(TAG, "completeConstruction: maxDepth=" + maxDepth);

            mStateStack = new StateInfo[maxDepth];
            mTempStateStack = new StateInfo[maxDepth];
            setupInitialStateStack();

            /** Sending SM_INIT_CMD message to invoke enter methods asynchronously */
            sendMessageAtFrontOfQueue(obtainMessage(SM_INIT_CMD, mSmHandlerObj));// 不同于4.0.4，比如：在UI线程中，调用状态机的start方法，这里只是把SM_INIT_CMD消息发送给HandlerThread中的Handler处理，初始状态的enter、exit方法，都是在状态机的HandlerThread线程中执行的，不会占用UI线程的资源^-^算是一个小改进吧

            if (mDbg) Log.d(TAG, "completeConstruction: X");
        }

StateMachine：

    /**
     * Enqueue a message to the front of the queue for this state machine.
     * Protected, may only be called by instances of StateMachine.
     */
    protected final void sendMessageAtFrontOfQueue(int what, Object obj) {
        mSmHandler.sendMessageAtFrontOfQueue(obtainMessage(what, obj));
    }