Android bindService流程

亦凉 2024-03-25 21:55 75阅读 0赞

## 一. 前言 ##

我们可以通过startService来启动一个服务, 当然也可以通过bindService绑定一个服务,本篇文章我们来讲一讲绑定服务的完整流程, 阅读此文之前,建议先阅读一下笔者的这三篇文章[ Android 进程间通信机制(三) 系统进程与应用进程通信][Android _]

[ Android 进程间通信机制(四) 应用进程启动过程][Android _ 1]

[Android 进程间通信机制(五) startService流程 ][Android _ startService_]

整个流程我们从 应用进程到AMS的的调用过程 和 Sevice的绑定过程 来梳理一下

## 二. 流程分析 ##

绑定服务,一般流程在客户端调用bindService()方法, 待绑定服务端的service成功后, 再回调客户端的ServiceConnection中的onServiceConnected()方法. 好了,接下来就一起看看代码

预先准备：自己写了一个客户端MyClient.apk 一个服务端MyService.apk

#### 2.1 App ---> AMS ####

比如客户端MyClient.apk 调用代码如下:

Intent intent = new Intent();
            ComponentName componentName = new ComponentName("com.example.mysevicejava",
                    "com.example.mysevicejava.MyService");
            intent.setComponent(componentName);
            this.bindService(intent, mServiceConnection, Context.BIND_AUTO_CREATE);

第一个参数传入Intent，第二个参数传入创建的ServiceConnection， ServiceConnection本身是一个接口. 其中包括两个回调方法, bindService()是在ContextWrapper.java类中实现的。

@Override
        public boolean bindService(Intent service, ServiceConnection conn,
                int flags) {
            return mBase.bindService(service, conn, flags);
        }

mBase是ContextImpl类型对象，调用ContextImpl的bindService()方法。

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

继续调用ContextImpl.java中的 bindServiceCommon 方法

private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
                String instanceName, Handler handler, Executor executor, UserHandle user) {
    
    ....
          // Keep this in sync with DevicePolicyManager.bindDeviceAdminServiceAsUser.
          // 先提前说一下, IServiceConnection 也是一个接口,继承android.os.IInterface 说明是一个Binder,用于跨进程通信用的, 后文有用到它的地方
            IServiceConnection sd;
    
           if (mPackageInfo != null) {
               //注释1
                if (executor != null) {
                    sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), executor, flags);
                } else {
                    sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);
                }
            } else {
                throw new RuntimeException("Not supported in system context");
            }
    
            //检查service intent的有效性, 在高于L版本之后, 启动servie必须是显示的intent
            //要带上包名和类名
            validateServiceIntent(service);
    
            //注释2
             int res = ActivityManager.getService().bindIsolatedService(
                    mMainThread.getApplicationThread(), getActivityToken(), service,
                    service.resolveTypeIfNeeded(getContentResolver()),
                    sd, flags, instanceName, getOpPackageName(), user.getIdentifier());
    }

注释1处创建sd对象

注释2处调用bindIsolatedService()方法与系统进程中的AMS交互

在注释1处调用了 LoadedApk类型的对象 mPackagelnfo 的getServiceDispatcher方法.

接着又调用 getServiceDispatcherCommon这个方法

private IServiceConnection getServiceDispatcherCommon(ServiceConnection c,
                Context context, Handler handler, Executor executor, int flags) {
    
        .....
          LoadedApk.ServiceDispatcher sd = null;
          ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map = mServices.get(context);
          
         //第一次绑定sd为null  executor为null
         if (sd == null) {
                    if (executor != null) {
                        sd = new ServiceDispatcher(c, context, executor, flags);
                    } else {
         //走这里的代码,创建一个ServiceDispatcher实例。
                        sd = new ServiceDispatcher(c, context, handler, flags);
                    }
    
        
         //创建好后, 用map存起来  key为 ServiceConnection对象(客户端传递过来的ServiceConnection), value为ServiceDispatcher对象
         map.put(c, sd);
    
        
         //返回一个InnerConnection对象。
         return sd.getIServiceConnection();
    }

在来看看 ServiceDispatcher这个类, 首先它属于LoadedApk.java中的一个静态类

/frameworks/base/core/java/android/app/LoadedApk.java

static final class ServiceDispatcher {
            private final ServiceDispatcher.InnerConnection mIServiceConnection;
    .....
    
            private static class ConnectionInfo {
                IBinder binder;
                IBinder.DeathRecipient deathMonitor;
            }
            
            //注释1 内部类 InnerConnection是一个Binder
            //看见这块比较熟悉的代码,在跨进程通信来看, 这里就属于服务端的代码, 那谁是客户端呢?
            //答案是 AMS 
            private static class InnerConnection extends IServiceConnection.Stub {
                @UnsupportedAppUsage
                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);
                    }
                }
            }
    
    
          //ServiceDispatcher构造方法
            @UnsupportedAppUsage
            ServiceDispatcher(ServiceConnection conn,
                Context context, Handler activityThread, int flags) {
            //创建一个InnerConnection对象，是一个IBinder
            mIServiceConnection = new InnerConnection(this);
            //将客户端conn赋值给mConnection
            mConnection = conn;
            mContext = context;
            mActivityThread = activityThread;
            mActivityExecutor = null;
            mLocation = new ServiceConnectionLeaked(null);
            mLocation.fillInStackTrace();
            mFlags = flags;
        }
    
    
    
            IServiceConnection getIServiceConnection() {
                return mIServiceConnection;
            }
    
    .....
    }

在看看IServiceConnection.aidl 文件, 用关键字oneway修饰,说明在远程调用时(是异步调用，即客户端AMS不会被阻塞), 它只是发送事务数据并立即返回, oneway修饰了的方法不可以有返回值.

/** @hide */
    oneway interface IServiceConnection {
        @UnsupportedAppUsage
        void connected(in ComponentName name, IBinder service, boolean dead);
    }

上面这段代码IServiceConnection 跨进程通信模型如下:

![0cfb1c6c8f1c47c192cc2a3e98ec13c9.png][]

**IServiceConnection 用于在 AMS 在bindService成功后通知app(此时AMS作为客户端, app进程作为服务端), 然后回调app的 ServiceConnection的 onServiceConnected方法.**

好了把注释1 和 注释2 分析完后, 先总结一下时序图:

![1cc840d434994e85aac7686ca13e7aa9.png][]

#### 2.2 Sevice绑定过程 ####

接下来就进入到 AMS 中

调用到ActivityManagerService的bindIsolatedService方法

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);
            }
    ....
    
    }

接下来调用 frameworks/base/services/core/java/com/android/server/am/ActiveServices.java

中的 bindServiceLocked 方法:

int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,
                String resolvedType, final IServiceConnection connection, int flags,
                String instanceName, String callingPackage, final int userId)
                throws TransactionTooLargeException {
        .....	
        ServiceRecord s = res.record;
    
    	boolean permissionsReviewRequired = false;
        .....
          //注释1记录需要bind的service
        AppBindRecord b = s.retrieveAppBindingLocked(service, callerApp);
        ConnectionRecord c = new ConnectionRecord(b, activity,
                        connection, flags, clientLabel, clientIntent,
                        callerApp.uid, callerApp.processName, callingPackage);
    
    
        //注释2 这个就是 bindservice()方法的第三个参数  Context.BIND_AUTO_CREATE
        if ((flags&Context.BIND_AUTO_CREATE) != 0) {
                    s.lastActivity = SystemClock.uptimeMillis();
                    //会调用到service服务端进程进行onCreate onBind
                    if (bringUpServiceLocked(s, service.getFlags(), callerFg, false,
                            permissionsReviewRequired) != null) {
                        return 0;
                    }
        }
        .....
     
       // 注释3   s为ServiceRecord  s.app为ProcessRecord  第一次绑定是s.app为null 
       // b.intent.received 为false 所以走else分支.
       
       if (s.app != null && b.intent.received) {
                    // Service is already running, so we can immediately
                    // publish the connection.
                    //直接翻译英文注释: 服务已经正在运行, 所以我们立马能回调 connection
                    //即回调 IServiceConnection 接口中的 connected(3个参数)方法了
                    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.
                    // 注释4 应用进程与服务进行绑定,并且服务已经调用过onUnbind方法
                    if (b.intent.apps.size() == 1 && b.intent.doRebind) {
                        requestServiceBindingLocked(s, b.intent, callerFg, true);
                    }
       } else if (!b.intent.requested) {
                  //注释5 如果应用进程没有发送过绑定service的请求, 第一次绑定会走这里
                  requestServiceBindingLocked(s, b.intent, callerFg, false);
       }
        .....
    }

先看注释1的调用代码

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;
        }

讲到这 有必要先介绍几个与 Service 关的对象类型 ，这样有助于对源码进行理解，  
如下所示

ServiceRecord ：用于描述一个 Service  
ProcessRecord : 一个进程的信息。  
ConnectionRecord ：用于描述应用进程和 Service 建立的一次通信。  
AppBindRecord ：**应用进程通过 Intent 绑定 Service 时，会通过 AppBindRecord  
来维护 Service 与应用程序进程之间的关联**。其内部存储了谁绑定的 Service  
( ProcessRecord 、被绑定的 Service ( AppBindRecord ）、绑定 Service Intent  
( IntentBindRecord ）和所有绑定通信记 的信息（ ArraySet<Connect onRecord ）。  
IntentBindRecord ：用于描述绑定 Service Intent

注释2处部分

在注释2处调用 bringUpServiceLocked 方法，在 bringUpServiceLocked 方法中又调用  
realStartServiceLocked 方法，最终由 ActivityThread 来调用 Service onCreate 方法启动  
Service ，这也说明了 bindService 方法内部会启动 Service

关于startService的启动流程 请查阅笔者的 [Android 进程间通信机制(五) startService流程][Android _ startService_]

注释3处部分:

s为ServiceRecord s.app为ProcessRecord 第一次绑定是s.app为null b.intent.received 为false 所以走else分支(走注释5处代码)

b.intent.received只有在服务端MyService执行 onBind()并且publishService()之后才为true

s.app是在realStartServiceLocked()的时候被赋值.

注释4处表示:应用进程与服务进行绑定,并且服务已经调用过onUnbind方法

继续分析 注释5 部分

注释5处表示: 如果应用进程没有发送过绑定service的请求,第一次绑定就会走这个分支

private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i,
                boolean execInFg, boolean rebind) throws TransactionTooLargeException {
    
    
     if ((!i.requested || rebind) && i.apps.size() > 0) {
                try {
                    bumpServiceExecutingLocked(r, execInFg, "bind");
                    r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
                    //这里就通过IApplicationThread进行跨进程通信, 跳转到app进程的 ActivityThread.java的scheduleBindService方法了
                    r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
                            r.app.getReportedProcState());
                    if (!rebind) {
                        i.requested = true;
                    }
                    i.hasBound = true;
                    i.doRebind = false;
    }

继续跳转到

frameworks/base/core/ java/and  oid/app/ ActivityTh read  . java 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());
                //发送BIND_SERVICE消息
                sendMessage(H.BIND_SERVICE, s);
            }
    
    
    //处理消息的代码:
     case BIND_SERVICE:
                        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
                        handleBindService((BindServiceData)msg.obj);
                        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                        break;
    ....

继续调用frameworks/base/core/java/android/app/ActivityThread java的handleBindService方法

private void handleBindService(BindServiceData data) {
     
         Service s = mServices.get(data.token); //1
         
         if (s != null) {
                try {
                    data.intent.setExtrasClassLoader(s.getClassLoader());
                    data.intent.prepareToEnterProcess();
                    try {
                        if (!data.rebind) { //2
                            IBinder binder = s.onBind(data.intent); //3
                            ActivityManager.getService().publishService(
                                    data.token, data.intent, binder); //4
                        } 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);
                    }
                }
    ....
    
    }

在1 处获取要绑定的 Service

在2处BindServiceData成员变量rebind值为false

在3处,就执行来调用 Service中的 onBind方法, 比如我自己写MyService.java

@Override
        public IBinder onBind(Intent intent) {
            Log.e("test", "==服务端==onBind========");
            // TODO: Return the communication channel to the service.
            return new MyBinder();
        }

如果 rebind 的值为 true 则调用 5处的 Service onRebind 方法

在4会调用  
ActivityManager.getService()的publishService方法，调用ActivityManagerService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");
                }
                mServices.publishServiceLocked((ServiceRecord)token, intent, service);
            }
        }

接着又会调用 mServices.publishServiceLocked((ServiceRecord)token, intent, service);

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 {
                                    //最重要的方法
                                    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);
                                }

**重点关注 c.conn.connected(r.name, service, false);**

可以再回过头看下2.1 小结中的 IServiceConnection 通信的示意图(见2.1小结的分析图)

调用 c.conn.connected方法，其中 c.conn指的是 IServiceConnection , 它的实现为ServiceDispatcher.InnerConnection ，实现代码在 /frameworks/base/core/java/android/app/LoadedApk.java 中

其中ServiceDispatcher 是LoadedApk 的内部类, 而InnerConnection又是ServiceDispatcher的内部类.

c.conn.connected(xxx) 就调用的如下的代码

private static class InnerConnection extends IServiceConnection.Stub {
                @UnsupportedAppUsage
                final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;
    
                InnerConnection(LoadedApk.ServiceDispatcher sd) {
                    mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
                }
                
                //会调用这里的方法
                public void connected(ComponentName name, IBinder service, boolean dead)
                        throws RemoteException {
                    LoadedApk.ServiceDispatcher sd = mDispatcher.get();
                    if (sd != null) {
                        sd.connected(name, service, dead);
                    }
                }
            }

继续调用 sd.connected(name, service, dead)方法:

public void connected(ComponentName name, IBinder service, boolean dead) {
                if (mActivityExecutor != null) {
                    mActivityExecutor.execute(new RunConnection(name, service, 0, dead));
                } else if (mActivityThread != null) {
                    //注释1
                    mActivityThread.post(new RunConnection(name, service, 0, dead));
                } else {
                    doConnected(name, service, dead);
                }
            }

注释1处调用 Handler 类型的对象 mActivityThread post 方法， mActivityThread  
际上指向的是H 。通过调用H 的post方法将 RunConnection 对象的内容运行在主线  
程中。 下面再看看RunConnection 里面的run方法

/frameworks/base/core/java/android/app/LoadedApk.java

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() {
                //上面传递进来的第三个参数 mCommand 为 0,所以走这里的代码
                    if (mCommand == 0) {
                        doConnected(mName, mService, mDead);
                    } else if (mCommand == 1) {
                        doDeath(mName, mService);
                    }
                }
    
                final ComponentName mName;
                final IBinder mService;
                final int mCommand;
                final boolean mDead;
            }

继续调用doConnected(mName, mService, mDead)方法

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.
                //这里就回调到了 客户端的  onServiceConnected 方法了
                if (service != null) {
                    mConnection.onServiceConnected(name, service);
                } else {
                    // The binding machinery worked, but the remote returned null from onBind().
                    mConnection.onNullBinding(name);
                }
    .....
    }

这样在客户端实现了 ServiceConnection 接口类的 onServiceConnected方法就会被执  
行。至此，Service 的绑定过程就分析完成。

## 三. 整体流程图 ##

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAbGVhcm5mcmFtZXdvcms_size_20_color_FFFFFF_t_70_g_se_x_16_pic_center][]

在自己写的demo(客户端 MyClient.apk 服务端MyService.apk)中加入log,也和上面分析的流程图是一致的

03-21 21:50:57.942  4221  9156 E test    : =ActiveServices===创建==scheduleCreateService==
    03-21 21:50:57.943  4221  9156 E test    : ===ActiveServices  scheduleBindService===
    03-21 21:50:57.945 29708 29708 E test    : =服务端MyService==onCreate=====
    03-21 21:50:57.946 29708 29708 E test    : ==服务端MyService==onBind========
    03-21 21:50:57.964 29831 29831 E test    :  客户端MyClient 回调方法 onServiceConnected

##  ##

[Android _]: https://blog.csdn.net/u012514113/article/details/129633900
[Android _ 1]: https://blog.csdn.net/u012514113/article/details/129649290
[Android _ startService_]: https://blog.csdn.net/u012514113/article/details/129558584
[0cfb1c6c8f1c47c192cc2a3e98ec13c9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/f27c6a14388d4d8c989166cfedbbe171.png
[1cc840d434994e85aac7686ca13e7aa9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/aee842bdb58d4b8c8a412f68d2a1994d.png
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAbGVhcm5mcmFtZXdvcms_size_20_color_FFFFFF_t_70_g_se_x_16_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/ba79210036f44a8aa848156fc0d7ae1a.png