android wifi状态机原理
从源代码角度去分析状态机的实现过程。
主要涉及到的文件有：
frameworks/base/wifi/java/android/net/wifi/WifiStateMachine.java
frameworks/base/core/java/com/android/internal/util/StateMachine.java
frameworks/base/core/java/com/android/internal/util/State.java
frameworks/base/core/java/com/android/internal/util/IState.java
其中IState是一个接口类：
上述的方法会由StateMachine来支配，决定何时调用，现有这个概念即可。
接着看StateMachine类中一些重要的内嵌类和函数。
public static class ProcessedMessageInfo {//包含一个状态的所有信息
private int what;
private State state;//这个经常用到，表示当前处于那个状态
private State orgState;//表示接收到消息的状态
........................................
ProcessedMessageInfo(Message message, State state, State orgState) {
update(message, state, orgState);//更新当前状态
}
..........................................
public void update(Message message, State state, State orgState) {
this.what = message.what;
this.state = state;
this.orgState = orgState;
}
.......................................
}
private static class ProcessedMessages {//保存最近处理的20条消息，具体包括state,发送的message等
private static final int DEFAULT_SIZE = 20;//默认的最大状态个数，这个不是指所有的状态，而是当前活动状态往父类追溯得到的所有类的状态
private Vector<ProcessedMessageInfo> mMessages = new Vector<ProcessedMessageInfo>();
private int mMaxSize = DEFAULT_SIZE;
....................................
ProcessedMessageInfo get(int index) {//根据索引获取状态信息
int nextIndex = mOldestIndex + index;
if (nextIndex >= mMaxSize) {
nextIndex -= mMaxSize;
}
if (nextIndex >= size()) {
return null;
} else {
return mMessages.get(nextIndex);
}
}
.........................................
void add(Message message, State state, State orgState) {//orgState为最底层状态节点，state为有能力处理message的节点，他们可能相等，或则state为orgState的祖类节点
mCount += 1;
if (mMessages.size() < mMaxSize) {
mMessages.add(new ProcessedMessageInfo(message, state, orgState));
} else {
ProcessedMessageInfo pmi = mMessages.get(mOldestIndex);
mOldestIndex += 1;
if (mOldestIndex >= mMaxSize) {
mOldestIndex = 0;
}
pmi.update(message, state, orgState);
}
}
}
private static class SmHandler extends Handler {
.................................
private StateInfo mStateStack[];//这里存放的是当前state以及父类的state
private int mStateStackTopIndex = -1;//mStateStack数组的下标索引
private StateInfo mTempStateStack[];//状态信息缓存区
private HaltingState mHaltingState = new HaltingState();//状态挂起时候才会用到，一般用不上
private QuittingState mQuittingState = new QuittingState();//状态退出时候才会用上，一般用不上
private StateMachine mSm;//全局的StateMachine引用，在构造函数中this指针赋的值
private HashMap<State, StateInfo> mStateInfo =
new HashMap<State, StateInfo>();//保存所有加入的state信息
private State mInitialState;//初始化的状态
private State mDestState;//切换时新的目标状态
@Override
public final void handleMessage(Message msg) {
processMsg(msg);//处理接收到的消息
performTransitions();//处理就状态到新状态的切换
if (mDbg) Log.d(TAG, "handleMessage: X");
}
..........................
}
到这里，还是先把wifistatemachine的状态图写出来，以便好理解。
比如，如果当前状态为mDriverFailedState,则上面mStateStack存放的是[mDefaultState，mDriverUnloadedState，mDriverFailedState]三个状态的信息
StateMachine的构造函数做了些什么？
protected StateMachine(String name) {
mSmThread = new HandlerThread(name);
mSmThread.start();
Looper looper = mSmThread.getLooper();
initStateMachine(name, looper);
}
而在initStateMachine方法中：
private void initStateMachine(String name, Looper looper) {
mName = name;
mSmHandler = new SmHandler(looper, this); //mSmHandler是一个全局的handler，后面常用到
}
private SmHandler(Looper looper, StateMachine sm) {
super(looper);
mSm = sm;//mSm是一个全局的变量，后面经常用到
addState(mHaltingState, null);//状态挂起的时候调用
addState(mQuittingState, null);//状态退出的时候调用
}
WifiStateMachine的构造函数主要做了些什么？
主要是调用addState方法将wifi中创建的状态加入状态机中，最后setInitialState来设置初始化状态。具体过程如下：
protected final void addState(State state, State parent) {//将state添加到父节点parent下，如果parent为null,则state作为父节点
mSmHandler.addState(state, parent);
}
private final StateInfo addState(State state, State parent) {
if (mDbg) {
Log.d(TAG, "addStateInternal: E state=" + state.getName()
+ ",parent=" + ((parent == null) ? "" : parent.getName()));
}
StateInfo parentStateInfo = null;
if (parent != null) {
parentStateInfo = mStateInfo.get(parent);//取出父节点的parentStateInfo信息
if (parentStateInfo == null) { //如果父节点为null,则递归调用,把当前节点作为父节点
// Recursively add our parent as it's not been added yet.
parentStateInfo = addState(parent, null);
}
}
StateInfo stateInfo = mStateInfo.get(state);//新节点，肯定为null了
if (stateInfo == null) {
stateInfo = new StateInfo();
mStateInfo.put(state, stateInfo);//将state和stateInfo放入哈系表中，以后根据state即可取出stateInfo信息，前面说过，全局变量mStateInfo哈系表保存了所有state信息
}
// Validate that we aren't adding the same state in two different hierarchies.
if ((stateInfo.parentStateInfo != null) && //新创建还没有赋值，肯定为null啦，否则就抛出异常了
(stateInfo.parentStateInfo != parentStateInfo)) {
throw new RuntimeException("state already added");
}
stateInfo.state = state;
stateInfo.parentStateInfo = parentStateInfo;//以后通过state可以找到父节点，一直递归，如果state的父节点为null，则表示到了顶部
stateInfo.active = false; //时候是当前活动状态标志
if (mDbg) Log.d(TAG, "addStateInternal: X stateInfo: " + stateInfo);
return stateInfo;
}
这样，通过上面的addState方法，最终形成了上图所示的树形结构。在使用之前，还要设置state的初始化状态：
/**
* Set the initial state. This must be invoked before
* and messages are sent to the state machine.
*
* @param initialState is the state which will receive the first message.
*/
protected final void setInitialState(State initialState) {
mSmHandler.setInitialState(initialState);
}
注释已经说的很清楚，这是第一次接收到消息时候进入的状态：
private final void setInitialState(State initialState) {
if (mDbg) Log.d(TAG, "setInitialState: initialState" + initialState.getName());
mInitialState = initialState;//先简单的保存到全局变量中，后续才用到
}
这样初始化工作完成，WifiStateMachine的构造函数最后调用start()来启动状态机，它的实现方法在父类StateMachine中：
public void start() {
// mSmHandler can be null if the state machine has quit.
if (mSmHandler == null) return;//mSmHandler引用在前面构造函数中就赋值了，肯定不为null了
/** Send the complete construction message */
mSmHandler.completeConstruction();
}
}
来看completeConstruction方法的实现：
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()) {//这个for循环就是遍历前面添加到哈系表中的状态，找出树的最大深度，根据前面的树形表可以看出，最大深度为5
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];//这个是最后存放当前活动state的，可以看到要得到最大深度的作用就是为了创建数组，因为当前活动state以及父类家族最多就为maxDepth
mTempStateStack = new StateInfo[maxDepth];//这个是暂时存放state的
setupInitialStateStack();
/**
* Construction is complete call all enter methods
* starting at the first entry.
*/
mIsConstructionCompleted = true;
mMsg = obtainMessage(SM_INIT_CMD);
invokeEnterMethods(0);
/**
* Perform any transitions requested by the enter methods
*/
performTransitions();
if (mDbg) Log.d(TAG, "completeConstruction: X");
}
接着下一句是setupInitialStateStack方法：
private final void setupInitialStateStack() {
if (mDbg) {
Log.d(TAG, "setupInitialStateStack: E mInitialState="
+ mInitialState.getName());
}
StateInfo curStateInfo = mStateInfo.get(mInitialState);//取出初始化state,前面已经赋值过，这里为WifiStateMachine中mInitialState对应的stateInfo
for (mTempStateStackCount = 0; curStateInfo != null; mTempStateStackCount++) {
mTempStateStack[mTempStateStackCount] = curStateInfo;//最后mTempStateStack存放的值为[mInitialState,mDefaultState]对应的stateInfo
curStateInfo = curStateInfo.parentStateInfo;
}
// Empty the StateStack
mStateStackTopIndex = -1;
moveTempStateStackToStateStack();
}
moveTempStateStackToStateStack方法就是将mTempStateStack的值倒序放到mStateStack中：
private final int moveTempStateStackToStateStack() {
int startingIndex = mStateStackTopIndex + 1;// -1 + 1 = 0；
int i = mTempStateStackCount - 1;//第一次进入，2 - 1 = 1;
int j = startingIndex;
while (i >= 0) {
if (mDbg) Log.d(TAG, "moveTempStackToStateStack: i=" + i + ",j=" + j);
mStateStack[j] = mTempStateStack[i];
j += 1;
i -= 1;
}
mStateStackTopIndex = j - 1;// 2 - 1 = 1
if (mDbg) {
Log.d(TAG, "moveTempStackToStateStack: X mStateStackTop="
+ mStateStackTopIndex + ",startingIndex=" + startingIndex
+ ",Top=" + mStateStack[mStateStackTopIndex].state.getName());
}
return startingIndex; //0
}这样，当前状态信息就保存在mStateStack中，为[mDefaultState, mInitialState]对应的状态信息。
回到completeConstruction中，接着invokeEnterMethods方法：
private final void invokeEnterMethods(int stateStackEnteringIndex) {
for (int i = stateStackEnteringIndex; i <= mStateStackTopIndex; i++) {//前面分析可以，mStateStackTopIndex为1
if (mDbg) Log.d(TAG, "invokeEnterMethods: " + mStateStack[i].state.getName());
mStateStack[i].state.enter();//依次调用活动状态的enter方法，可以看到是从最顶层父类依次往下调用的
mStateStack[i].active = true; //把当前state置为true
}
}
mDefaultState重写enter方法，父类State的enter方法什么也不做；InitialState有重写enter方法：
class InitialState extends State {
@Override
//TODO: could move logging into a common class
public void enter() {
......................................
if (WifiNative.isDriverLoaded()) {
transitionTo(mDriverLoadedState);//如果我们打开过wifi，状态就会切换到mDriverLoadedState去了
}
else {
transitionTo(mDriverUnloadedState);//第一次打开是没有load过的，所以进入unload状态
}
.................................
}
}
protected final void transitionTo(IState destState) {//IState是所有state的接口类
mSmHandler.transitionTo(destState);调用handler方法来处理
}
private final void transitionTo(IState destState) {
mDestState = (State) destState;//先保存到变量中，后续真正状态切换时候才用到
if (mDbg) Log.d(TAG, "StateMachine.transitionTo EX destState" + mDestState.getName());
}
这样invokeEnterMethods方法就完成了，接着是performTransitions方法，这是真正处理状态切换的方法了：
private void performTransitions() {
.....................
State destState = null;
while (mDestState != null) {
......................................
destState = mDestState;//destState为mDriverUnLoadedState
mDestState = null;
..............................
StateInfo commonStateInfo = setupTempStateStackWithStatesToEnter(destState);
invokeExitMethods(commonStateInfo);
int stateStackEnteringIndex = moveTempStateStackToStateStack();
invokeEnterMethods(stateStackEnteringIndex);
moveDeferredMessageAtFrontOfQueue();
}
if (destState != null) {
if (destState == mQuittingState) {
cleanupAfterQuitting();
} else if (destState == mHaltingState) {
mSm.halting();
}
}
}
setupTempStateStackWithStatesToEnter方法主要是把当前活动state家族放入mTempStateStack中，并且返回顶层节点的信息，这样，mTempStateStack保存信息为[mDriverUnLoadedState, mDefaultState]的信息；
invokeExitMethods方法则是从当前活动state顶层节点一次调用exit方法,并且设置state的active标记为false;这里要注意当前活动的还是是mStateStack中的信息，即[mDefaultState, mInitialState]对应的状态信息，exit方法一般是做一些善后工作。处理完成后
mStateStackTopIndex又自减为-1。
moveTempStateStackToStateStack和invokeEnterMethods方法前面已经分析过。完成后mStateStack的状态信息变为[mDefaultState,mDriverUnLoadedState]
最后一个函数moveDeferredMessageAtFrontOfQueue刷新消息队列的排序。该方法就是将mDeferredMessages容器中的消息按先后顺序发送出去，然后清空容器。至于消息是如何加入容器的，后面遇到再分析。
这样start方法就完成，整个WifiStateMachine构造函数也建立完成了。
如果我们打开wifi,会在WifiService中调用setWifiEnabled - >mWifiStateMachine.setWifiEnabled来启动。setWifiEnabled的状态切换过程为：
public void setWifiEnabled(boolean enable) {
mLastEnableUid.set(Binder.getCallingUid());
if (enable) {
/* Argument is the state that is entered prior to load */
sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_STATE_ENABLING, 0));
sendMessage(CMD_START_SUPPLICANT);
} else {
sendMessage(CMD_STOP_SUPPLICANT);
/* Argument is the state that is entered upon success */
sendMessage(obtainMessage(CMD_UNLOAD_DRIVER, WIFI_STATE_DISABLED, 0));
}
}
sendMessage方法是StateMachine实现的，它封装了Handler类的sendMessage方法，会被SmHandler类的handleMessage来接收处理。而它是调用一下两个方法来处理消息的：
processMsg(msg);
performTransitions();先看第一个：
private final void processMsg(Message msg) {
StateInfo curStateInfo = mStateStack[mStateStackTopIndex];//mStateStack保存信息的顺序为顶层节点->底层节点，mStateStackTopIndex为数组个数，这里取出的就为最底层节点的状态信息
if (mDbg) {
Log.d(TAG, "processMsg: " + curStateInfo.state.getName());
}
while (!curStateInfo.state.processMessage(msg)) {//所以从底层节点开始往上遍历，调用processMessage来处理消息，直到找到一个可以处理的节点后返回HANDLED(true),条件退出
/**
* Not processed
*/
curStateInfo = curStateInfo.parentStateInfo;
if (curStateInfo == null) {//找到顶层节点了，才用unhandledMessage，它不做什么事情，打印一句LOG信息而已
/**
* No parents left so it's not handled
*/
mSm.unhandledMessage(msg);
if (isQuit(msg)) {//如果命令是SM_QUIT_CMD才会退出，一般情况下是不会退出的
transitionTo(mQuittingState);
}
break;
}
if (mDbg) {
Log.d(TAG, "processMsg: " + curStateInfo.state.getName());
}
}
/**
* Record that we processed the message
*/
if (curStateInfo != null) {
State orgState = mStateStack[mStateStackTopIndex].state;
mProcessedMessages.add(msg, curStateInfo.state, orgState);//保存处理processMessage的消息到mProcessedMessages中，作为一个记录，一般保存最近的20条，这个最大值可以自己定义
} else {
mProcessedMessages.add(msg, null, null);
}
}
这时mStateStack的状态信息变为[mDefaultState, mDriverUnLoadedState]，先所以调用mDriverUnLoadedState的processMessage方法，而前面发送的消息为：
sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_STATE_ENABLING, 0));
sendMessage(CMD_START_SUPPLICANT);
第一句的CMD_LOAD_DRIVER,发送给应用层的消息为WIFI_STATE_ENABLING：
class DriverUnloadedState extends State {
@Override
public void enter() {
if (DBG) log(getName() + "\n");
EventLog.writeEvent(EVENTLOG_WIFI_STATE_CHANGED, getName());
}
@Override
public boolean processMessage(Message message) {
if (DBG) log(getName() + message.toString() + "\n");
switch (message.what) {
case CMD_LOAD_DRIVER:
mWifiP2pChannel.sendMessage(WIFI_ENABLE_PENDING);//这是发送消息给WifiP2pService，WifiP2pService会响应并返回消息WIFI_ENABLE_PROCEED，其中过程有点复杂，后续再分析
transitionTo(mWaitForP2pDisableState);//状态切换到了mWaitForP2pDisableState，其他好像没有做什么
break;
case WifiP2pService.P2P_ENABLE_PENDING:
mReplyChannel.replyToMessage(message, P2P_ENABLE_PROCEED);
break;
default:
return NOT_HANDLED;
}
EventLog.writeEvent(EVENTLOG_WIFI_EVENT_HANDLED, message.what);
return HANDLED;
}
}
WaitForP2pDisableState的enter做什么了？
状态已经进入mWaitForP2pDisableState中了：
class WaitForP2pDisableState extends State {
.............................
@Override
public boolean processMessage(Message message) {
case WifiP2pService.WIFI_ENABLE_PROCEED: //响应WifiP2pService消息
//restore argument from original message (CMD_LOAD_DRIVER)
message.arg1 = mSavedArg;
transitionTo(mDriverLoadingState);
break;
case CMD_LOAD_DRIVER:
case CMD_UNLOAD_DRIVER:
case CMD_START_SUPPLICANT:
..........................
deferMessage(message);
.............................
}
deferMessage将消息放入mDeferredMessages容器中，前面有提及过，作用是要把消息保存起来，等切换到下一个状态后，再将消息发送出去，让下一个状态接收；接下来的performTransitions方法中会将消息发送出去，并且在切换下一个状态前清空容器。
这时候状态在WaitForP2pDisableState中，WifiP2pService接收到消息WIFI_ENABLE_PENDING后，返回WIFI_ENABLE_PROCEED作为响应；
所以执行transitionTo(mDriverLoadingState)进入下一个状态。
processMsg就处理完成了，接着的performTransitions前面已经分析过，主要工作为调用当前状态的exit方法；切换新状态到mSupplicantStartingState，并调用新状态的enter方法，静等下一个消息的到来。
根据前面的分析可知，这时候先执行的是mDriverLoadingState的enter方法：
class DriverLoadingState extends State {
@Override
public void enter() {
if (DBG) log(getName() + "\n");
EventLog.writeEvent(EVENTLOG_WIFI_STATE_CHANGED, getName());
final Message message = new Message();
message.copyFrom(getCurrentMessage());
/* TODO: add a timeout to fail when driver load is hung.
* Similarly for driver unload.
*/
new Thread(new Runnable() {
public void run() {
mWakeLock.acquire();
//enabling state
switch(message.arg1) {
case WIFI_STATE_ENABLING:
setWifiState(WIFI_STATE_ENABLING);
break;
if(WifiNative.loadDriver()) {
if (DBG) log("Driver load successful");
sendMessage(CMD_LOAD_DRIVER_SUCCESS);
} else {
loge("Failed to load driver!");
switch(message.arg1) {
case WIFI_STATE_ENABLING:
setWifiState(WIFI_STATE_UNKNOWN);
break;
case WIFI_AP_STATE_ENABLING:
setWifiApState(WIFI_AP_STATE_FAILED);
break;
}
sendMessage(CMD_LOAD_DRIVER_FAILURE);
}
mWakeLock.release();
}
}).start();
@Override
public boolean processMessage(Message message) {
if (DBG) log(getName() + message.toString() + "\n");
switch (message.what) {
case CMD_LOAD_DRIVER_SUCCESS:
transitionTo(mDriverLoadedState);
break;
case CMD_LOAD_DRIVER_FAILURE:
transitionTo(mDriverFailedState);
break;
case CMD_LOAD_DRIVER:
case CMD_UNLOAD_DRIVER:
case CMD_START_SUPPLICANT:
case CMD_STOP_SUPPLICANT:
case CMD_START_AP:
case CMD_STOP_AP:
case CMD_START_DRIVER:
case CMD_STOP_DRIVER:
case CMD_SET_SCAN_MODE:
case CMD_SET_SCAN_TYPE:
case CMD_SET_HIGH_PERF_MODE:
case CMD_SET_COUNTRY_CODE:
case CMD_SET_FREQUENCY_BAND:
case CMD_START_PACKET_FILTERING:
case CMD_STOP_PACKET_FILTERING:
deferMessage(message);
break;
default:
return NOT_HANDLED;
}
EventLog.writeEvent(EVENTLOG_WIFI_EVENT_HANDLED, message.what);
return HANDLED;
}
enter线程中的消息为前面发送的WIFI_STATE_ENABLING，setWifiState的作用是发送广播通知应用层wifi状态的改变，并且加载JNI的wifi驱动，成功后还发送CMD_LOAD_DRIVER_SUCCESS消息。
接着第二句命令CMD_START_SUPPLICANT，状态在mDriverLoadingState中，执行processMessage方法，这时候会先接收前面的延时消息CMD_LOAD_DRIVER_SUCCESS，接着接收CMD_LOAD_DRIVER，CMD_START_SUPPLICANT
状态就切换到了mDriverLoadedState，并且将其他两条消息延后再传给下一个状态。
后续WifiService会根据逻辑需求，发送各种命令过来进行状态的切换，但流程都和上述分析的一样，状态机能确保各种状态有条不紊的切换并保持控制流程的清晰明了。
最后画一幅流程图如下：
