1、Android深入四大组件三Service的绑定过程Android深入四大组件(三)Service的绑定过程1.ContextImpl到ActivityManageService的调用过程我们可以用bindService方法来绑定Service,它的实现在ContextWrapper中,代码如下所示。 frameworks/base/core/Java/Android/content/ContextWrapper.java Override public boolean bindService(Intent service, ServiceConnection conn, int flags)
2、 return mBase.bindService(service, conn, flags);查看ContextImpl的bindService方法: frameworks/base/core/java/android/app/ContextImpl.java Override public boolean bindService(Intent service, ServiceConnection conn, int flags) warnIfCallingFromSystemProcess(); return bindServiceCommon(service, conn, flags,
3、mMainThread.getHandler(), Process.myUserHandle(); 在bindService方法中,又return了bindServiceCommon方法,代码如下所示。 frameworks/base/core/java/android/app/ContextImpl.javaprivate boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler handler, UserHandle user) IServiceConnection sd; if
4、 (conn = null) throw new IllegalArgumentException(connection is null); if (mPackageInfo != null) sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);/1 else throw new RuntimeException(Not supported in system context); validateServiceIntent(service); try . /* * 2 */ int re
5、s = ActivityManagerNative.getDefault().bindService( mMainThread.getApplicationThread(), getActivityToken(), service, service.resolveTypeIfNeeded(getContentResolver(), sd, flags, getOpPackageName(), user.getIdentifier(); . catch (RemoteException e) throw e.rethrowFromSystemServer(); 在注释1处调用了LoadedApk
6、类型的对象mPackageInfo的getServiceDispatcher方法,它的主要作用是将ServiceConnection封装为IServiceConnection类型的对象sd,从IServiceConnection的名字我们就能得知它实现了Binder机制,这样Service的绑定就支持了跨进程。接着在注释2处我们又看见了熟悉的代码,最终会调用AMS的bindService方法。 ContextImpl到ActivityManageService的调用过程如下面的时序图所示。2.Service的绑定过程AMS的bindService方法代码如下所示。 frameworks/bas
7、e/services/core/java/com/android/server/am/ActivityManagerService.java public int bindService(IApplicationThread caller, IBinder token, Intent service, String resolvedType, IServiceConnection connection, int flags, String callingPackage, int userId) throws TransactionTooLargeException enforceNotIsol
8、atedCaller(bindService);. synchronized(this) return mServices.bindServiceLocked(caller, token, service, resolvedType, connection, flags, callingPackage, userId); bindService方法最后会调用ActiveServices类型的对象mServices的bindServiceLocked方法: frameworks/base/services/core/java/com/android/server/am/ActiveService
9、s.java int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service, String resolvedType, final IServiceConnection connection, int flags, String callingPackage, final int userId) throws TransactionTooLargeException . if (flags&Context.BIND_AUTO_CREATE) != 0) s.lastActivity = System
10、Clock.uptimeMillis(); /* * 1 */ if (bringUpServiceLocked(s, service.getFlags(), callerFg, false, permissionsReviewRequired) != null) return 0; . if (s.app != null & b.intent.received) /2 try c.conn.connected(s.name, b.intent.binder);/3 catch (Exception e) . if (b.intent.apps.size() = 1 & b.intent.do
11、Rebind) /4 requestServiceBindingLocked(s, b.intent, callerFg, true);/5 else if (!b.intent.requested) /6 requestServiceBindingLocked(s, b.intent, callerFg, false);/7 getServiceMap(s.userId).ensureNotStartingBackground(s); finally Binder.restoreCallingIdentity(origId); return 1;在注释1处会bringUpServiceLoc
12、ked方法,在bringUpServiceLocked方法中又会调用realStartServiceLocked方法,最终由ActivityThread来调用Service的onCreate方法启动Service,在注释2处s.app != null 表示Service已经运行,其中s是ServiceRecord类型对象,app是ProcessRecord类型对象。b.intent.received表示当前应用程序进程的Client端已经接收到绑定Service时返回的Binder,这样应用程序进程的Client端就可以通过Binder来获取要绑定的Service的访问接口。注释3处调用c.c
13、onn的connected方法,其中c.conn指的是IServiceConnection,它的具体实现为ServiceDispatcher.InnerConnection,其中ServiceDispatcher是LoadedApk的内部类,InnerConnection的connected方法内部会调用H的post方法向主线程发送消息,从而解决当前应用程序进程和Service跨进程通信的问题,在后面会详细介绍这一过程。 在注释4处如果当前应用程序进程的Client端第一次与Service进行绑定的,并且Service已经调用过onUnBind方法,则需要调用注释5的代码。 注释6处如果应用程
14、序进程的Client端没有发送过绑定Service的请求,则会调用注释7的代码,注释7和注释5的代码区别就是最后一个参数rebind为false,表示不是重新绑定。 接着我们查看注释7的requestServiceBindingLocked方法,代码如下所示。 frameworks/base/services/core/java/com/android/server/am/ActiveServices.javaprivate final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i, boolea
15、n execInFg, boolean rebind) throws TransactionTooLargeException . if (!i.requested | rebind) & i.apps.size() 0) /1 try bumpServiceExecutingLocked(r, execInFg, bind); r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE); r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
16、r.app.repProcState);/2 . . return true;注释1处i.requested表示是否发送过绑定Service的请求,从前面的代码得知是没有发送过,因此,!i.requested为true。从前面的代码得知rebind值为false,那么(!i.requested | rebind)的值为true。如果IntentBindRecord中的应用程序进程记录大于0,则会调用注释2的代码,r.app.thread的类型为IApplicationThread,它的实现我们已经很熟悉了,是ActivityThread的内部类ApplicationThread,schedul
17、eBindService方法如下所示。 frameworks/base/core/java/android/app/ActivityThread.java 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;
18、s.rebind = rebind; if (DEBUG_SERVICE) Slog.v(TAG, scheduleBindService token= + token + intent= + intent + uid= + Binder.getCallingUid() + pid= + Binder.getCallingPid(); sendMessage(H.BIND_SERVICE, s); 首先将Service的信息封装成BindServiceData对象,需要注意的BindServiceData的成员变量rebind的值为false,后面会用到它。接着将BindServiceData
19、传入到sendMessage方法中。sendMessage向H发送消息,我们接着查看H的handleMessage方法。 frameworks/base/core/java/android/app/ActivityThread.javapublic void handleMessage(Message msg) if(DEBUG_MESSAGES) Slog.v(TAG, handling: + codeToString(g.what); switch (msg.what) . case BIND_SERVICE: Trace.traceBegin(Trace.TRACE_TAG_ACTIVI
20、TY_MANAGER, serviceBind); handleBindService(BindServiceData)msg.obj); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; . . . H在接收到BIND_SERVICE类型消息时,会在handleMessage方法中会调用handleBindService方法: frameworks/base/core/java/android/app/ActivityThread.java private void handleBindService(BindServiceDa
21、ta data) Service s = mServices.get(data.token);/1 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) /2 IBinder binder = s.onBind(data.int
22、ent);/3 ActivityManagerNative.getDefault().publishService( data.token, data.intent, binder);/4 else s.onRebind(data.intent);/5 ActivityManagerNative.getDefault().serviceDoneExecuting( data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0); ensureJitEnabled(); . . 注释1处获取要绑定的Service 。注释2处的BindServiceData的成员变量
23、rebind的值为false,这样会调用注释3处的代码来调用Service的onBind方法,这样Service处于绑定状态了。如果rebind的值为true就会调用注释5处的Service的onRebind方法,结合前文的bindServiceLocked方法的注释4处,我们得知如果当前应用程序进程的Client端第一次与Service进行绑定,并且Service已经调用过onUnBind方法,则会调用Service的onRebind方法。 接着查看注释4的代码,实际上是调用AMS的publishService方法。 讲到这,先给出这一部分的代码时序图(不包括Service启动过程)我们接着
24、来查看AMS的publishService方法,代码如下所示。 frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.javapublic void publishService(IBinder token, Intent intent, IBinder service) . synchronized(this) if (!(token instanceof ServiceRecord) throw new IllegalArgumentException(Invalid service
25、token); mServices.publishServiceLocked(ServiceRecord)token, intent, service); publishService方法中,调用了ActiveServices类型的mServices对象的publishServiceLocked方法: frameworks/base/services/core/java/com/android/server/am/ActiveServices.java void publishServiceLocked(ServiceRecord r, Intent intent, IBinder servi
26、ce) final long origId = Binder.clearCallingIdentity(); try . for (int conni=r.connections.size()-1; conni=0; conni-) ArrayList clist = r.connections.valueAt(conni); for (int i=0; iclist.size(); i+) . try c.conn.connected(r.name, service);/1 catch (Exception e) . serviceDoneExecutingLocked(r, mDestro
27、yingServices.contains(r), false); finally Binder.restoreCallingIdentity(origId); 注释1处的代码,我在前面介绍过,c.conn指的是IServiceConnection,它的具体实现为ServiceDispatcher.InnerConnection,其中ServiceDispatcher是LoadedApk的内部类,ServiceDispatcher.InnerConnectiond的connected方法的代码如下所示。 frameworks/base/core/java/android/app/LoadedA
28、pk.javastatic final class ServiceDispatcher . private static class InnerConnection extends IServiceConnection.Stub final WeakReference mDispatcher; InnerConnection(LoadedApk.ServiceDispatcher sd) mDatcher=new WeakReference(sd); public void connected(ComponentName name, IBinder service) throws Remote
29、Exception LoadedApk.ServiceDispatcher sd = mDispatcher.get(); if (sd != null) sd.connected(name, service);/1 . 在注释1处调用了ServiceDispatcher 类型的sd对象的connected方法,代码如下所示。 frameworks/base/core/java/android/app/LoadedApk.java public void connected(ComponentName name, IBinder service) if (mActivityThread !=
30、null) mActivityThread.post(new RunConnection(name, service, 0);/1 else doConnected(name, service); 注释1处调用Handler类型的对象mActivityThread的post方法,mActivityThread实际上指向的是H。因此,通过调用H的post方法将RunConnection对象的内容运行在主线程中。RunConnection的定义如下所示。 frameworks/base/core/java/android/app/LoadedApk.java private final class RunConnection implements Runnable RunConnection(ComponentName name, IBinder service
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