BindService详解

1 bindService介绍

1.1 bindService介绍

bindService 是 Android 中用于绑定到服务的方法。它的核心功能是建立一个客户端与服务之间的连接,使得客户端可以与服务进行交互。

在解析 bindService 的源码之前,我们需要先了解它的使用方法。bindService 是一个 Activity 的方法,它需要三个参数:

  1. Intent:这是一个明确指示要启动的服务的对象。
  2. ServiceConnection:这是一个回调接口,当我们与服务建立连接时,系统将调用这个接口。
  3. flags:这是一个可选的标志,用于指定绑定服务的额外选项。

1.2 bindService使用

bindService 的例子:

Intent intent = new Intent(this, MyService.class);
ServiceConnection serviceConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        // 当服务连接成功时调用
    }
 
    @Override
    public void onServiceDisconnected(ComponentName name) {
        // 当服务连接断开时调用
    }
};
 
boolean bindServiceResult = bindService(intent, serviceConnection, Context.BIND_AUTO_CREATE);

1.3 bindService 的大致流程

bindService 的大致流程:

  1. 当你调用 bindService 方法时,ContextImpl 类中的 bindService 方法会被调用。
  2. 这个方法会创建一个 ServiceConnection 的代理,并通过 ActivityManagerNativeActivityManagerService 请求绑定服务。
  3. ActivityManagerService 会处理绑定服务的请求,如果服务不存在,它会创建服务的实例。
  4. 服务创建后,ActivityManagerService 会通过 ServiceDispatcher 回调你提供的 ServiceConnection 的代理。
  5. 代理接收回调后,将其转发给你的 ServiceConnection 实现。

2 源码解析

2.1 binderService流程

从上面简单使用实例看到,我们一般通过bindService(intent, connection, Context.BIND_AUTO_CREATE)开始。这个方法会走到ContextWrapper#bindService()

public boolean bindService(@RequiresPermission @NonNull Intent service,
            @BindServiceFlags int flags, @NonNull @CallbackExecutor Executor executor,
            @NonNull ServiceConnection conn) {
        throw new RuntimeException("Not implemented. Must override in a subclass.");
}

继续往下到ContextImpl#bindService()

@Override
public boolean bindService(Intent service, ServiceConnection conn, int flags) {
    warnIfCallingFromSystemProcess();
    return bindServiceCommon(service, conn, flags, null, mMainThread.getHandler(), null,getUser());
}

这里直接到ContextImpl#bindServiceCommon

private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
            String instanceName, Handler handler, Executor executor, UserHandle user) {
    ...
    int res = ActivityManager.getService().bindIsolatedService(
                mMainThread.getApplicationThread(), getActivityToken(), service,
                service.resolveTypeIfNeeded(getContentResolver()),
                sd, flags, instanceName, getOpPackageName(), user.getIdentifier());
}

ContextImpl#bindServiceCommon前面主要是进行一些条件检查,我们直接跳过,其中关键的是调用到了ActivityManager.getService().bindIsolatedService也就是ActivityManagerService#bindIsolatedService

public int bindIsolatedService(IApplicationThread caller, IBinder token, Intent service, String resolvedType, IServiceConnection connection, int flags, String instanceName, String callingPackage, int userId) throws TransactionTooLargeException {
    ...
    synchronized(this) {
        return mServices.bindServiceLocked(caller, token, service,
                                           resolvedType, connection, flags,
                                           instanceName, callingPackage, userId);
    }
}

bindIsolatedService最后调到了mServices.bindServiceLocked。这个mServices是一个ActiveServices。

final ActiveServices mServices;
public ActivityManagerService(Injector injector, ServiceThread handlerThread) {
    ...
    mServices = hasHandlerThread ? new ActiveServices(this) : null;
    ...
}

它是在AMS的构造函数里面初始化的。我们继续看ActiveServices#bindServiceLocked里面做了啥。

int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,
            String resolvedType, final IServiceConnection connection, int flags,
            String instanceName, String callingPackage, final int userId)
            throws TransactionTooLargeException {
    ... //省略一些条件检查
    ServiceLookupResult res = retrieveServiceLocked(service, instanceName,
                                                    resolvedType,
                                                    callingPackage,callingPid,
                                                    callingUid, userId,
                                                    true,callerFg, isBindExternal,
                                                    allowInstant);
    ...
    final ServiceRecord serviceRecord = s;
    final Intent serviceIntent = service;
    RemoteCallback callback = new RemoteCallback(
        new RemoteCallback.OnResultListener() {
            @Override
            public void onResult(Bundle result) {
                bringUpServiceLocked(serviceRecord,serviceIntent.getFlags(),
                                     callerFg, false, false);
            }
        }
    ...
    try {
        if (unscheduleServiceRestartLocked(s, callerApp.info.uid, false)) {
            if (DEBUG_SERVICE)
                Slog.v(TAG_SERVICE, "BIND SERVICE WHILE RESTART PENDING: " + s);
        }
        AppBindRecord b = s.retrieveAppBindingLocked(service, callerApp);
        ConnectionRecord c = new ConnectionRecord(b, activity,
                    connection, flags, clientLabel, clientIntent,
                    callerApp.uid, callerApp.processName, callingPackage);
        
        IBinder binder = connection.asBinder();
        s.addConnection(binder, c);
        b.connections.add(c);
        if (activity != null) {
            activity.addConnection(c);
        }
        b.client.connections.add(c);
        c.startAssociationIfNeeded();
        ...
        if (s.app != null && b.intent.received) {
                // Service is already running, so we can immediately
                // publish the connection.
                try {
                    c.conn.connected(s.name, b.intent.binder, false);
                } catch (Exception e) {
                    Slog.w(TAG, "Failure sending service " + s.shortInstanceName
                            + " 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) {
                    requestServiceBindingLocked(s, b.intent, callerFg, true);
                }
            } else if (!b.intent.requested) {
                requestServiceBindingLocked(s, b.intent, callerFg, false);
            }
    } finally {
            Binder.restoreCallingIdentity(origId);
        }
}

ActiveServices#bindServiceLocked这个方法分两种情况:

  1. ActiveServices#bringUpServiceLocked()
  2. ActiveServices#requestServiceBindingLocked()

为什么分为两种情况,这涉及到 A进程访问B进程时的几种状态:

  1. 进程B没有启动,即整个B进程都没有启动
  2. 进程B启动了,但是里面的Service没创建出来
  3. 进程B启动了,里面的Service也创建了,但是Service没有被绑定过,回调onBind()
  4. 进程B启动了,里面的Service也创建了,但是Service已经被绑定过,回调onRebind()

状态1、2对应代码中的情况1;状态3、4对应代码中的情况2。

第一种情况ActiveServices#bringUpServiceLockedService启动流程,我们另一篇幅再介绍,这里略去不表。

接着往下看ActiveServices#bindServiceLocked

这里创建了一个ConnectionRecord对象,传入了服务端和客户端的信息,然后和IServiceConnection的binder对象一起,存入ServiceRecord的connections中,

private final ArrayMap<IBinder, ArrayList<ConnectionRecord>> connections
    = new ArrayMap<IBinder, ArrayList<ConnectionRecord>>();

然后以binder为key,以ConnectionRecord组成的ArrayList存入mServiceConnections中

ArrayList<ConnectionRecord> clist = mServiceConnections.get(binder);
if (clist == null) {
    clist = new ArrayList<>();
    mServiceConnections.put(binder, clist);
}
clist.add(c);

mServiceConnections中存放的是所有绑定的service连接。

/**
 * All currently bound service connections.  Keys are the IBinder of
 * the client's IServiceConnection.
 */
final ArrayMap<IBinder, ArrayList<ConnectionRecord>> mServiceConnections = new ArrayMap<>();

第一次service起来一般不会走下面的connected流程,这里先不看,后面再看。

if (s.app != null && b.intent.received) {
    // Service is already running, so we can immediately publish the connection.
    try {
        c.conn.connected(s.name, b.intent.binder, false);
    }
}

2.2 onBind流程

我们回过头来继续看ActiveServices#bindServiceLocked后面的流程。

private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i, boolean execInFg, boolean rebind) throws TransactionTooLargeException {
    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);
            r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
                                             r.app.getReportedProcState());
            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;
}

bumpServiceExecutingLocked主要是把相关的信息更新到ServiceRecord里面,这里就不看了。

重点来看r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind, r.app.getReportedProcState());

这里r.app的app是ServiceRecord的成员变量ProcessRecord

ProcessRecord app;      // where this service is running or null.

而thread是ProcessRecord的成员变量IApplicationThread。

IApplicationThread thread;  // the actual proc...  may be null only if
                            // 'persistent' is true (in which case we
                            // are in the process of launching the app)

IApplicationThread这个我们很熟悉,它的实现是ActivityThread的内部类ApplicationThread

private class ApplicationThread extends IApplicationThread.Stub

直接看ApplicationThread#scheduleBindService

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());
               sendMessage(H.BIND_SERVICE, s);
}

继续看

case BIND_SERVICE:
	Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
	handleBindService((BindServiceData)msg.obj);
	Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
	break;

这里调到了handleBindService。

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) {
                    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);
                }
            } 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);
            }
        }
    }
}

这里根据service的token从service的集合中找到对应的service。

final ArrayMap<IBinder, Service> mServices = new ArrayMap<>();

然后调用service的onBind方法,并将Intent作为参数传递过去了,然后返回服务端的IBinder对象,最后调用ActivityManagerService#publishService发布服务。

2.3 发布服务

AMS的publishService很简单,最终又回到了ActiveServices里面了。

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");
        }
        mServices.publishServiceLocked((ServiceRecord)token, intent, service);
    }
}

publishServiceLocked里面会把前面保存到ServiceRecord里面的相关信息再取出来。

void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
    final long origId = Binder.clearCallingIdentity();
    try {
        if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "PUBLISHING " + r
                                  + " " + intent + ": " + service);
        if (r != null) {
            Intent.FilterComparison filter = new Intent.FilterComparison(intent);
            IntentBindRecord b = r.bindings.get(filter);
            if (b != null && !b.received) {
                b.binder = service;
                b.requested = true;
                b.received = true;
                ArrayMap<IBinder, ArrayList<ConnectionRecord>> connections =
                    r.getConnections();
                for (int conni = connections.size() - 1; conni >= 0; conni--) {
                    ArrayList<ConnectionRecord> clist = connections.valueAt(conni);
                    for (int i=0; i<clist.size(); i++) {
                        ConnectionRecord c = clist.get(i);
                        if (!filter.equals(c.binding.intent.intent)) {
                            if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Not publishing
                                                      to: " + c);
                            if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Bound intent: " +
                                                      c.binding.intent.intent);
                            if (DEBUG_SERVICE) Slog.v(
                                TAG_SERVICE, "Published intent: " + intent);
                                continue;
                            }
                       if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Publishing to: " + c);
                        try {
                            c.conn.connected(r.name, service, false);
                        } catch (Exception e) {
                            Slog.w(TAG, "Failure sending service " +
                                   r.shortInstanceName
                                  + " to connection " + c.conn.asBinder()
                                  + " (in " + c.binding.client.processName + ")", e);
                        }
                    }
                }
            }

            serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);
        }
    } finally {
        Binder.restoreCallingIdentity(origId);
    }
}

2.4 onServiceConnected流程

这里调用 c.conn.connected(r.name, service, false);

IServiceConnection的实现类是android.app.LoadedApk的静态内部类ServiceDispatcher里面。

static final class ServiceDispatcher {
    private static class InnerConnection extends IServiceConnection.Stub {
        final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;

        InnerConnection(LoadedApk.ServiceDispatcher sd) {
            mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
        }

        public void connected(ComponentName name, IBinder service, boolean dead)
            throws RemoteException {
            LoadedApk.ServiceDispatcher sd = mDispatcher.get();
            if (sd != null) {
                sd.connected(name, service, dead);
            }
        }
    }
    
    public void connected(ComponentName name, IBinder service, boolean dead) {
        if (mActivityExecutor != null) {
            mActivityExecutor.execute(new RunConnection(name, service, 0, dead));
        } else if (mActivityThread != null) {
            mActivityThread.post(new RunConnection(name, service, 0, dead));
        } else {
            doConnected(name, service, dead);
        }
    }
}

这里直接调用了LoadedApk.ServiceDispatche#connected

connected函数里面三个分支最终都会走到connected里面。

public void doConnected(ComponentName name, IBinder service, boolean dead) {
    ...
    if (service != null) {
        // A new service is being connected... set it all up.
        info = new ConnectionInfo();
        info.binder = service;
        info.deathMonitor = new DeathMonitor(name, service);
        try {
            service.linkToDeath(info.deathMonitor, 0);
            mActiveConnections.put(name, info);
        } catch (RemoteException e) {
            // This service was dead before we got it...  just
            // don't do anything with it.
            mActiveConnections.remove(name);
            return;
        }
    }
    
    // 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) {
        mConnection.onServiceConnected(name, service);
    } else {
        // The binding machinery worked, but the remote returned null from onBind().
        mConnection.onNullBinding(name);
    }
}

这里会将绑定的信息放到mActiveConnections的集合里面,然后回调ServiceConnection#onServiceConnected。这时客户端就收到了onServiceConnected。

2.5 bringUpServiceLocked逻辑

最后来看bringUpServiceLocked的逻辑。

if ((flags&Context.BIND_AUTO_CREATE) != 0) {
    s.lastActivity = SystemClock.uptimeMillis();
    if (bringUpServiceLocked(s, service.getFlags(), callerFg, false,
                             permissionsReviewRequired) != null) {
        return 0;
    }
}

如果service没有运行时,就会走bringUpServiceLocked逻辑,然后直接返回。

private String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg, boolean whileRestarting, boolean permissionsReviewRequired)
    throws TransactionTooLargeException {
    ...
    if (app != null && app.thread != null) {
    	app.addPackage(r.appInfo.packageName, r.appInfo.longVersionCode,
                   mAm.mProcessStats);
    	realStartServiceLocked(r, app, execInFg);
        return null;
    }
    ...
}

如果APP 已经创建了,即进程已经启动了,就启动service,走realStartServiceLocked。

/**
 * Note the name of this method should not be confused with the started services concept.
 * The "start" here means bring up the instance in the client, and this method is called
 * from bindService() as well.
 */
private final void realStartServiceLocked(ServiceRecord r,
                     ProcessRecord app, boolean execInFg) throws RemoteException {
    r.setProcess(app);
    r.restartTime = r.lastActivity = SystemClock.uptimeMillis();

    final boolean newService = app.startService(r);
    bumpServiceExecutingLocked(r, execInFg, "create");
    mAm.updateLruProcessLocked(app, false, null);
    updateServiceForegroundLocked(r.app, /* oomAdj= */ false);
    mAm.updateOomAdjLocked(app, OomAdjuster.OOM_ADJ_REASON_START_SERVICE);
    
   ...
   app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
   app.thread.scheduleCreateService(r, r.serviceInfo,
                    mAm.compatibilityInfoForPackage(r.serviceInfo.applicationInfo),
                    app.getReportedProcState());
   r.postNotification();
    ...
}

参数app是一个 ProcessRecord 对象,每启动一个app就创建了一个进程,进程信息就保存在ProcessRecord里面。app.thread就是ApplicationThread对象。

app.thread.scheduleCreateService(),会调用Handler发送一个CREATE_SERVICE消息,然后执行handleCreateService()方法:

private void handleCreateService(CreateServiceData data) {
    ...
    ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
    Application app = packageInfo.makeApplication(false, mInstrumentation);
    java.lang.ClassLoader cl = packageInfo.getClassLoader();
    service = packageInfo.getAppFactory()
        .instantiateService(cl, data.info.name, data.intent);
    // Service resources must be initialized with the same loaders as the application
    // context.
    context.getResources().addLoaders(
        app.getResources().getLoaders().toArray(new ResourcesLoader[0]));

    context.setOuterContext(service);
    service.attach(context, this, data.info.name, data.token, app,
                   ActivityManager.getService());
    service.onCreate();
    mServices.put(data.token, service);
    try {
        ActivityManager.getService().serviceDoneExecuting(
            data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}

这里通过类加载器和反射加载的Service,并把它保存到mServices集合中。

final ArrayMap<IBinder, Service> mServices = new ArrayMap<>();

为什么要将service put到mServices中,因为service只能创建一次,只能bind一次,下次再调用bindService进行绑定服务时,先从mServices中寻找,如果找到了则判断service是否绑定了,如果还没有绑定,则调onBind进行绑定,如果已经绑定了,则调用onRebind。这个过程在handleBindService()中:

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) {
                    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);
                }
            } 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);
            }
        }
    }
}

最后bringUpServiceLocked返回null,继续走ActiveServices#bindServiceLocked后面的流程。

Service的app进程没有启动的逻辑这里就不再展开讨论。

2.6 总结

BindService详解_第1张图片

3 疑问

3.1 onServiceConnected()和onBind()的时机与顺序

我们主要看ActiveServices#bindServiceLocked中下面这段

if (s.app != null && b.intent.received) {
    // Service is already running, so we can immediately
    // publish the connection.
    try {
        c.conn.connected(s.name, b.intent.binder, false);
    } catch (Exception e) {
        Slog.w(TAG, "Failure sending service " + s.shortInstanceName
               + " 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) {
        requestServiceBindingLocked(s, b.intent, callerFg, true);
    }
} else if (!b.intent.requested) {
    requestServiceBindingLocked(s, b.intent, callerFg, false);
}

条件1:s.app != null && b.intent.received

s.app != null这个条件一般应该都满足。那么b.intent.received是什么时候设置为true的呢?

答案就在ActiveServices#publishServiceLocked的时候

void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
     if (r != null) {
         if (b != null && !b.received) {
             b.binder = service;
             b.requested = true;
             b.received = true;
         }
     }
}

再来看b.intent.apps.size() == 1 && b.intent.doRebind这个条件。

先来看``b.intent.apps.size() == 1这个条件,它的设置在ServiceRecord#retrieveAppBindingLocked`中

public AppBindRecord retrieveAppBindingLocked(Intent intent,ProcessRecord app) {
	Intent.FilterComparison filter = new Intent.FilterComparison(intent);
    IntentBindRecord i = bindings.get(filter);
    if (i == null) {
        i = new IntentBindRecord(this, filter);
        bindings.put(filter, i);
    }
    AppBindRecord a = i.apps.get(app);
    if (a != null) {
        return a;
    }
    a = new AppBindRecord(this, i, app);
    i.apps.put(app, a);
    return a;
}

所以,对于已经绑定过service的client来说,这个值应该会是1。

再来看 b.intent.doRebind这个条件

doRebind设置为true的时机,也就是应用端收到UnbindService之后。

void unbindFinishedLocked(ServiceRecord r, Intent intent, boolean doRebind) {
    if (b != null) {
        if (b.apps.size() > 0 && !inDestroying) {
            // Applications have already bound since the last
            // unbind, so just rebind right here.
            boolean inFg = false;
            for (int i=b.apps.size()-1; i>=0; i--) {
                ProcessRecord client = b.apps.valueAt(i).client;
                if (client != null && client.setSchedGroup
                    != ProcessList.SCHED_GROUP_BACKGROUND) {
                    inFg = true;
                    break;
                }
            }
            try {
                requestServiceBindingLocked(r, b, inFg, true);
            } catch (TransactionTooLargeException e) {
                // Don't pass this back to ActivityThread, it's unrelated.
            }
        } else {
            // Note to tell the service the next time there is a new client.
            b.doRebind = true;
        }
    }
}

doRebind设置为false的时机:在每一次重新绑定之后,都会把,这个逻辑在前面的requestServiceBindingLocked和移除conn的时候:

private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i, boolean execInFg, boolean rebind) throws TransactionTooLargeException {
    ...
    if ((!i.requested || rebind) && i.apps.size() > 0) {
        if (!rebind) {
            i.requested = true;
        }
        i.hasBound = true;
        i.doRebind = false;
    }
}
void removeConnectionLocked(ConnectionRecord c, ProcessRecord skipApp,
            ActivityServiceConnectionsHolder skipAct) {
    ...
    b.intent.hasBound = false;
    // Assume the client doesn't want to know about a rebind;
    // we will deal with that later if it asks for one.
    b.intent.doRebind = false;
}

所以,这里分几种情况:

  1. 如果service是第一次调用bindService,那么此时received是false,就会直接走!b.intent.requested分支;

  2. 如果service已经绑定过了,那么直接调用c.conn.connected,客户端收到onServiceConnected回调;

    而且,如果之前有unBind过,那么就会再次调用onBind。

3.2 AMS进程的 conn.connected 是如何调用到app进程的connection.onServiceConnected()方法的?

先看下app进程的ServiceConnection对象是如何转为IServiceConnection对象的,app调用bindService方法进行绑定服务时会在ContextImpl#bindServiceCommon方法中对参数conn对象进行封装,转换为IServiceConnection对象sd,

private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
                                  UserHandle user) {
    IServiceConnection sd;
    if (conn == null) {
        throw new IllegalArgumentException("connection is null");
    }
    if (mPackageInfo != null) {
        sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
                                               mMainThread.getHandler(), flags);
	...
}

mPackageInfo时是LoadedApk对象,LoadedApk#getServiceDispatcher方法:

public final IServiceConnection getServiceDispatcher(ServiceConnection c,
        Context context, Handler handler, int flags) {
    synchronized (mServices) {
        LoadedApk.ServiceDispatcher sd = null;
        ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map =
            mServices.get(context);
        if (map != null) {
            sd = map.get(c);
        }
        if (sd == null) {
            sd = new ServiceDispatcher(c, context, handler, flags);
            if (map == null) {
                map = new ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>();
                mServices.put(context, map);
            }
            map.put(c, sd);
        } else {
            sd.validate(context, handler);
        }
        return sd.getIServiceConnection();
    }
}

static final class ServiceDispatcher {
	private final ServiceDispatcher.InnerConnection mIServiceConnection;
	...
	private static class InnerConnection extends IServiceConnection.Stub {
        final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;

        InnerConnection(LoadedApk.ServiceDispatcher sd) {
            mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
        }

        public void connected(ComponentName name, IBinder service) throws RemoteException {
            LoadedApk.ServiceDispatcher sd = mDispatcher.get();
            if (sd != null) {
                sd.connected(name, service);
            }
        }
    }

	...

    IServiceConnection getIServiceConnection() {
        return mIServiceConnection;
    }
    ...
}

也就是说客户端进程的bindService方法会把传递进去的ServiceConnection conn参数转为InnerConnection对象sd,InnerConnection实现了IServiceConnection接口,并且是Stub类,而AMS进程的conn对象也实现了IServiceConnection接口,是个Proxy类。
也就是AMS进程调用 conn.connected 方法最终调用到app进程的connection.onServiceConnected()方法的过程是一个Binder机制跨进程调用的过程,这个过程中AMS进程是客户端(IServiceConnection.Stub.Proxy),app进程是服务端(IServiceConnection.Stub)。

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