Service的绑定过程
Service的绑定过程
服务的绑定也算是开发中比较常用的功能，在上下文环境中通过bindService就可以绑定一个服务，通过追踪bindService的源码可以知道，最后会调用到父类ContextWrapper中，在这个类中又调用了mBase的bindService方法，mBase的实现是ContextImpl《Context创建》，部分源码如下(ContextWrapper中)：
//Context类型，具体实现类是ContextImpl
Context mBase;
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
return mBase.bindService(service, conn, flags);
}
由于bindService的具体实现是在ContextImpl类中，那么就来查看下ContextImpl的bindService方法：
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, mMainThread.getHandler(), getUser());
}
ContextImpl的bindService方法又调用了bindServiceCommon方法：
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler
handler, UserHandle user) {
...............
try {
.............
//关键代码1
int res = ActivityManager.getService().bindService(
mMainThread.getApplicationThread(), getActivityToken(), service,
service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, getOpPackageName(), user.getIdentifier());
.............
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
在关键代码1处，ActivityManager.getService()是AMS的代理对象，这里通过跨进程通信调用到了AMS的方法中，查看下AMS的bindService方法：
public int bindService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags, String callingPackage,
int userId) throws TransactionTooLargeException {
enforceNotIsolatedCaller("bindService");
..................
synchronized(this) {
return mServices.bindServiceLocked(caller, token, service,
resolvedType, connection, flags, callingPackage, userId);
}
}
在上述方法中，又调用了ActiveServices的bindServiceLocked方法：
int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, final IServiceConnection connection, int flags,
String callingPackage, final int userId) throws TransactionTooLargeException {
......................
if (s.app != null && b.intent.received) {
try {
c.conn.connected(s.name, b.intent.binder, false);
} catch (Exception e) {
Slog.w(TAG, "Failure sending service " + s.shortName
+ " to connection " + c.conn.asBinder()
+ " (in " + c.binding.client.processName + ")", e);
}
// If this is the first app connected back to this binding,
// and the service had previously asked to be told when
// rebound, then do so.
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
//关键代码2
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {
//关键代码3
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
......................
}
在关键代码2和关键代码3处，调用了requestServiceBindingLocked方法：
private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i,
boolean execInFg, boolean rebind) throws TransactionTooLargeException {
if (r.app == null || r.app.thread == null) {
// If service is not currently running, can't yet bind.
return false;
}
if (DEBUG_SERVICE) Slog.d(TAG_SERVICE, "requestBind " + i + ": requested=" + i.requested
+ " rebind=" + rebind);
if ((!i.requested || rebind) && i.apps.size() > 0) {
try {
bumpServiceExecutingLocked(r, execInFg, "bind");
r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
//关键代码4
r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
r.app.repProcState);
if (!rebind) {
i.requested = true;
}
i.hasBound = true;
i.doRebind = false;
} catch (TransactionTooLargeException e) {
// Keep the executeNesting count accurate.
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Crashed while binding " + r, e);
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
throw e;
} catch (RemoteException e) {
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Crashed while binding " + r);
// Keep the executeNesting count accurate.
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
return false;
}
}
return true;
}
在关键代码4处，r.app.thread是ApplicaitonThread的代理对象，这里是AMS向客户端发起了跨进程通信请求，调用ApplicaitonThread中的scheduleBindService方法：
public final void scheduleBindService(IBinder token, Intent intent,
boolean rebind, int processState) {
updateProcessState(processState, false);
BindServiceData s = new BindServiceData();
s.token = token;
s.intent = intent;
s.rebind = rebind;
if (DEBUG_SERVICE)
Slog.v(TAG, "scheduleBindService token=" + token + " intent=" + intent + " uid="
+ Binder.getCallingUid() + " pid=" + Binder.getCallingPid());
//关键代码5
sendMessage(H.BIND_SERVICE, s);
}
在关键代码5处，发送了一个绑定服务的消息给H，H类中的handleMessage方法：
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
在H类中收到绑定服务消息后又调用了ActivityThread的handleBindService方法:
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
if (DEBUG_SERVICE)
Slog.v(TAG, "handleBindService s=" + s + " rebind=" + data.rebind);
if (s != null) {
try {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
try {
if (!data.rebind) {
//关键代码6
IBinder binder = s.onBind(data.intent);
ActivityManager.getService().publishService(
data.token, data.intent, binder);
} else {
s.onRebind(data.intent);
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
}
ensureJitEnabled();
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to bind to service " + s
+ " with " + data.intent + ": " + e.toString(), e);
}
}
}
}
在关键代码6处，调用Service的onBind方法返回binder对象，这个binder对象就是我们自己创建的(aidl的stub的实现类)，然后在通过AMS的publishService方法发布该binder服务，下面看下AMS的publishService方法：
public void publishService(IBinder token, Intent intent, IBinder service) {
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
if (!(token instanceof ServiceRecord)) {
throw new IllegalArgumentException("Invalid service token");
}
//关键代码7
mServices.publishServiceLocked((ServiceRecord)token, intent, service);
}
}
在关键代码7处调用了ActiveServices的publishServiceLocked方法：
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
final long origId = Binder.clearCallingIdentity();
try {
//关键代码8 c.conn是IServiceConnection类型的
c.conn.connected(r.name, service, false);
} catch (Exception e) {
Slog.w(TAG, "Failure sending service " + r.name +
" to connection " + c.conn.asBinder() +
" (in " + c.binding.client.processName + ")", e);
}
}
关键代码8处的c.conn的类型是IServiceConnection，它的具体实现是LoadedApk的内部类ServiceDispatcher的内部类InnerConnection：
public final class LoadedApk {
...................
static final class ServiceDispatcher {
...................
private final ServiceDispatcher.InnerConnection mIServiceConnection;
//关键代码9
private static class InnerConnection extends IServiceConnection.Stub {
final WeakReference mDispatcher;
InnerConnection(LoadedApk.ServiceDispatcher sd) {
mDispatcher = new WeakReference(sd);
}
public void connected(ComponentName name, IBinder service, boolean dead)
throws RemoteException {
LoadedApk.ServiceDispatcher sd = mDispatcher.get();
if (sd != null) {
//关键代码10
sd.connected(name, service, dead);
}
}
}
//LoadedApk.ServiceDispatcher的connected方法
public void connected(ComponentName name, IBinder service, boolean dead) {
if (mActivityThread != null) {
//关键代码11
mActivityThread.post(new RunConnection(name, service, 0, dead));
} else {
//关键代码12
doConnected(name, service, dead);
}
}
}
}
在关键代码9处InnerConnection具体实现了IServiceConnection.Stub，IServiceConnection是个aidl接口，所以InnerConnection具备跨进程通信的能力，而在关键代码8处connected方法的调用其实就是调用了InnerConnection的connected方法，在connected方法中的关键代码10处调用了sd的connected方法，sd是LoadedApk.ServiceDispatcher类型的，在sd的connected方法中的关键代码11处mActivityThread是一个Handler(其真身是ActivityThread中的H)，通过H将程序回调到主线程中执行，由于RunConnection是个Runnable，所以会执行RunConnection的run方法，RunConnection源码如下：
private final class RunConnection implements Runnable {
RunConnection(ComponentName name, IBinder service, int command, boolean dead) {
mName = name;
mService = service;
mCommand = command;
mDead = dead;
}
public void run() {
if (mCommand == 0) {
//关键代码13
doConnected(mName, mService, mDead);
} else if (mCommand == 1) {
doDeath(mName, mService);
}
}
final ComponentName mName;
final IBinder mService;
final int mCommand;
final boolean mDead;
}
由关键代码12和关键代码13可知，最终程序会执行到ServiceDispatcher的doConnected方法中，doConnected源码如下：
public void doConnected(ComponentName name, IBinder service, boolean dead) {
.......................
// If there was an old service, it is now disconnected.
if (old != null) {
mConnection.onServiceDisconnected(name);
}
if (dead) {
mConnection.onBindingDied(name);
}
// If there is a new viable service, it is now connected.
if (service != null) {
//关键代码14
mConnection.onServiceConnected(name, service);
} else {
// The binding machinery worked, but the remote returned null from onBind().
mConnection.onNullBinding(name);
}
}
由关键代码14处可知，调用了mConnection的onServiceConnected方法，而mConnection的类型是ServiceConnection，其实这个mConnection对象就是我们binderService方法中传递的自己创建的ServiceConnection对象，由于该对象无法进行跨进程通信，所以在需要跟AMS进行跨进程通信的时候用的都是一个跟它相对应的InnerConnection对象，客户端同时持有了这两个对象，这样需要跨进程的时候就使用InnerConnection，我们在客户端绑定服务时会向AMS发起跨进程通信，AMS处理完毕会回调InnerConnection的connected方法，在connected方法中就会调用客户端传入的ServiceConnection对象的onServiceConnected方法，这样服务的绑定就完成了。