bindService 绑定服务过程
我们直接看 ContextWrapper 类中的 bindService 函数
//ContextWrapper.java
public class ContextWrapper extends Context {
Context mBase;
...
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
return mBase.bindService(service, conn, flags);
}
...
}这里调用方式跟 startService 相似，都是调用 ContextImpl 内部函数，直接看 ContextImpl 的 bindService 函数
//ContextImpl.java
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, mMainThread.getHandler(),
Process.myUserHandle());
}我们看 bindServiceCommon，代码如下:
//ContextImp.java
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler handler, UserHandle user) {
...
1. 调用 LoadApk 类型的对象 mPackageInfo 的 getServiceDispatcher 函数，它的主要作用就是将 ServiceConnection 封装为 IServiceConncet 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。
if (mPackageInfo != null) {
sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);
} else {
throw new RuntimeException("Not supported in system context");
}
validateServiceIntent(service);
try {
IBinder token = getActivityToken();
if (token == null && (flags&BIND_AUTO_CREATE) == 0 && mPackageInfo != null
&& mPackageInfo.getApplicationInfo().targetSdkVersion
< android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
flags |= BIND_WAIVE_PRIORITY;
}
service.prepareToLeaveProcess(this);
2. 获得 AMS 的代理，调用 bindService 函数，将会传递到 AMS 中
int res = ActivityManager.getService().bindService(
mMainThread.getApplicationThread(), getActivityToken(), service,
service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, getOpPackageName(), user.getIdentifier());
if (res < 0) {
throw new SecurityException(
"Not allowed to bind to service " + service);
}
return res != 0;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
调用 IActivityManager 的 bindService 函数，最终也还是会回到 AMS 中 bindService 函数，下
Service 绑定过程
收到 ContextImp 向 AMS 发送过来的 bindService 请求，代码如下
//AMS.java
/**
* 通过 ContextImpl 调用，中间进程间通信传递过来的
*/
public int bindService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags, String callingPackage, int userId) throws TransactionTooLargeException {
...
synchronized(this) {
//调用 ActiveService 的 bindServiceLocked 函数
return mServices.bindServiceLocked(caller, token, service,
resolvedType, connection, flags, callingPackage, userId);
}
}回调到 AMS 的 bindService 函数中，内部又调用 ActiveService 的 bindServiceLocked 函数进行传递，这里可以看到 ActiveService 不管是 start 还是 bind 最后都是在 ActiveService 中处理 Service 的启动逻辑。下面调用代码如下:
//ActiveServie.java
int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, final IServiceConnection connection, int flags,
String callingPackage, final int userId) throws TransactionTooLargeException {
....
1. 调用 ServiceRecord 的 retrieveAppBindingLocked 函数来获取 AppBindRecord
retrieveAppBindingLocked 函数内部创建 IntentBindRecord ,并对 IntentBindRecord 的成员变量进行赋值。
AppBindRecord b = s.retrieveAppBindingLocked(service, callerApp);
ConnectionRecord c = new ConnectionRecord(b, activity,
connection, flags, clientLabel, clientIntent);
IBinder binder = connection.asBinder();
...
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
2. 在 bringUpServiceLocked 函数的内部中调用了 realStartServiceLocked 函数，最终由 ActivityThread 来调用 Service 的 onCreate 函数启动 Service.
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false,
permissionsReviewRequired) != null) {
return 0;
}
}
....
3. 表示 Server 已经运行，其中 s 是 ServiceRecord 对象，app 是 ProcessRecord 类型对象，b.intent.received 表示当前应用程序进程已经接收到绑定服务的 Service 是返回回来的 Binder,
if (s.app != null && b.intent.received) {
// Service is already running, so we can immediately
// publish the connection.
try {
4. 调用 IServiceConnect 的connected 函数，具体实现在 @see ServiceDispatcher.InnerConnection，
c.conn.connected(s.name, b.intent.binder, false);
} catch (Exception e) {
...
}
5. 如果当前应用程序进程是第一个与 Service 进行绑定的，并且 Service 已经调用过 onUnBind 函数，则需要调用注释
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
6. 调用内部 requestServiceBindingLocked 函数
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {7. 如果应用程序进程的 Client 端没有发送过绑定 Service 的请求，则会调用注释 8
8.表示不是重新绑定
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
getServiceMapLocked(s.userId).ensureNotStartingBackgroundLocked(s);
} finally {
Binder.restoreCallingIdentity(origId);
}
return 1;
}我们看注释 6 如果当前应用程序进程是第一个与 Service 进行绑定的，并且 Service 已经调用过 onUnBind 函数。
//ActiveServices.java
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);
/**
* 1. i.requested 表示是否发送过绑定的请求，这里上上一步知道是发送过的，因为 为 false, rebind 为true ,所以前面为 true,
* i.apps.size() 其中 i 是 IntentBindRecord 对象，AMS 会为每个绑定 Service 的Intent 分配一个 IntentBindRecord 类型的对象。
*/
if ((!i.requested || rebind) && i.apps.size() > 0) {
try {
bumpServiceExecutingLocked(r, execInFg, "bind");
r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
//2. 调用 IApplicationThread 对象
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) {
...
throw e;
} catch (RemoteException e) {
...
return false;
}
}
return true;
}会调用注释 2 ，通过 IApplicationThread 与 ActivityThread 应用程序进程通信，代码如下:
//ActivityThread#ApplicationThread.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;
s.rebind = rebind;
...
//1.
sendMessage(H.BIND_SERVICE, s);
}//ActivityThread.java
private void sendMessage(int what, Object obj) {
继续调用内部重载函数 what = H.LAUNCH_ACTIVITY
sendMessage(what, obj, 0, 0, false);
}
private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
if (DEBUG_MESSAGES) Slog.v(
TAG, "SCHEDULE " + what + " " + mH.codeToString(what)
+ ": " + arg1 + " / " + obj);
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
if (async) {
msg.setAsynchronous(true);
}
2. 通过 H 的 Handler 将 what = H.LAUNCH_ACTIVITY 消息 what 发送出去
mH.sendMessage(msg);
}这里跟 startService 一样最后都是 通过 H 来通知bindService，下面代码如下:
//ActivityThread.java
//ActivityThread.java
public final class ActivityThread {
//初始化 H 类
final H mH = new H();
/**
* H 继承自 handler 是应用程序进程中主线程的消息管理类
*/
private class H extends Handler {
...
public static final int CREATE_SERVICE = 114;
....
public void handleMessage(Message msg) {
...
case BIND_SERVICE:
//调用 handleBindService
handleBindService((BindServiceData)msg.obj);
break;
...
}
}
}接下来我们看 handleUnbindService 函数具体实现:
//ActivityThread.java
private void handleBindService(BindServiceData data) {
/**
* 1. 获取需要绑定的 Service
*/
Service s = mServices.get(data.token);
if (s != null) {
try {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
try {
/**
* 2.没有经过绑定
*/
if (!data.rebind) {
/**
* 3. 调动 Service 生命周期 onBind 函数
*/
IBinder binder = s.onBind(data.intent);
/**
* 4. 调用 AMS 的 publishService 函数
*/
ActivityManager.getService().publishService(
data.token, data.intent, binder);
} else {
/**
* 5.如果已经经过绑定调用 onRebind 生命周期函数
*/
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) {
...
}
}
}这一步算是对 Service 进行开始执行生命周期函数了，如果 data.rebind 为 false 那么说明没有绑定，执行 s.onBind(data.intent); 生命周期函数，下面我们来看注释 4 调用 AMS 的 publishService ,代码如下:
//AMS.java
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);
}
}内部调用 ActiveServices 的 publishServiceLocked 函数
//ActiveServices.java
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
final long origId = Binder.clearCallingIdentity();
try {
...
if (r != null) {
Intent.FilterComparison filter
= new Intent.FilterComparison(intent);
IntentBindRecord b = r.bindings.get(filter);
...
for (int conni=r.connections.size()-1; conni>=0; conni--) {
ArrayList<ConnectionRecord> clist = r.connections.valueAt(conni);
for (int i=0; i<clist.size(); i++) {
ConnectionRecord c = clist.get(i);
.....
try {
//1.
c.conn.connected(r.name, service, false);
} catch (Exception e) {
...
}
}
}
}
serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);
}
} finally {
Binder.restoreCallingIdentity(origId);
}
}在注释1 处调用了 ServiceDispatcher 类型的 sd 对象的 connected 函数，代码如下：
//LoadedApk.java
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) {
//1.
sd.connected(name, service, dead);
}
}
}
public void connected(ComponentName name, IBinder service, boolean dead) {
if (mActivityThread != null) {
//2.
mActivityThread.post(new RunConnection(name, service, 0, dead));
} else {
doConnected(name, service, dead);
}
}这里首先通过进程间通信 AMS 发到 InnerConnection 的 connected 函数，然后调用 LoadedApk 的 connected 函数，最后执行 注释 2 的 post 函数， 代码如下：
//LoadedApk.java
private final class RunConnection implements Runnable {
RunConnection(ComponentName name, IBinder service, int command, boolean dead) {
mName = name;
...
}
public void run() {
if (mCommand == 0) {
doConnected(mName, mService, mDead);
} else if (mCommand == 1) {
doDeath(mName, mService);
}
}
}调用 doConnected 函数，代码如下:
public void doConnected(ComponentName name, IBinder service, boolean dead) {
ServiceDispatcher.ConnectionInfo old;
ServiceDispatcher.ConnectionInfo info;
synchronized (this) {
...
// 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 service, it is now connected.
if (service != null) {
/**
* 1. 调用了 ServiceConnection 类型的对象 mConnection 的 onServiceConnected 函数，这样在客户端实现了 ServiceConnection 接口，那么就会被执行。
*/
mConnection.onServiceConnected(name, service);
}
}通过上面代码的注释 1 我们知道，只要客户端通过如下代码绑定，那么就会回调到 onServiceConnected 回调，
bindService(new Intent(XXXX,XXXX), new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.d(TAG,"绑定成功");
}
@Override
public void onServiceDisconnected(ComponentName name) {
Log.d(TAG,"绑定失败，或者取消绑定");
}
})至此，整个 bindService 过程就分析完成。
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