service启动流程

1、以start方式启动

（1）原应用进程---AMS

startService

public class ContextWrapper extends Context {
      Context mBase;
      ......
      protected void attachBaseContext(Context base) {
          if (mBase != null) {
              throw new IllegalStateException("Base context already set");
          }
          mBase = base;
       }
       ......
       @Override
       public ComponentName startService(Intent service) {
          return mBase.startService(service);
       }
       ......
}

mBase来历

//====ActivityThread.java=====
private Activity performLaunchActivity(...){
    ......
    ContextImpl appContext = createBaseContextForActivity(r); //代码①
    Activity activity = null;
    ......
    activity.attach(appContext,...);//代码②
    ......
}

//跟进代码①
private ContextImpl createBaseContextForActivity(ActivityClientRecord r) {
    ......
    ContextImpl appContext = ContextImpl.createActivityContext(
            this, r.packageInfo, r.activityInfo, r.token, displayId, r.overrideConfig);
    ......
    return appContext;
}

//==========ContextImpl.java=======
static ContextImpl createActivityContext(...){
     ......
     ContextImpl context = new ContextImpl(...);
     .....
     return context;
}

//跟进代码②
//======Activity.java extends ContextThemeWrapper extends ContextThemeWrapper extends ContextWrapper extends Context===
final void attach(Context context,...){
     attachBaseContext(context);
     ......
}

protected void attachBaseContext(Context newBase) {
    super.attachBaseContext(newBase);
    ......
}

//======ContextThemeWrapper.java======
@Override
protected void attachBaseContext(Context newBase) {
    super.attachBaseContext(newBase);
}
//========ContextWrapper.java=====
protected void attachBaseContext(Context base) {
    if (mBase != null) {
        throw new IllegalStateException("Base context already set");
    }
    mBase = base;
}

所以mBase就是ContextImpl的实例。

class ContextImpl extends Context {
     ......
}

/

@Override
public ComponentName startService(Intent service) {
    warnIfCallingFromSystemProcess();
    return startServiceCommon(service, false, mUser);
}

private ComponentName startServiceCommon(Intent service, boolean requireForeground,
        UserHandle user) {
    try {
        ......
        ComponentName cn = ActivityManager.getService().startService(
            mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
                        getContentResolver()), requireForeground,
                        getOpPackageName(), user.getIdentifier());
        ......
        return cn;
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}

在上一篇文章中提到过，ActivityManager.getService()实际上就是获取AMS在当前进程的远程代理Proxy，这里不赘述了。

//=========ActivityManagerService.java============
......
final ActiveServices mServices;
......
@Override
public ComponentName startService(IApplicationThread caller, Intent service,
        String resolvedType, boolean requireForeground, String callingPackage, int userId)
        throws TransactionTooLargeException {
    ......
    synchronized(this) {
        final int callingPid = Binder.getCallingPid(); //调用者进程id
        final int callingUid = Binder.getCallingUid();//调用者用户id
        final long origId = Binder.clearCallingIdentity();
        ComponentName res;
        try {
            res = mServices.startServiceLocked(caller, service,
                    resolvedType, callingPid, callingUid,
                    requireForeground, callingPackage, userId);
        } finally {
            Binder.restoreCallingIdentity(origId);
        }
        return res;
    }
}

//

（2）AMS到ApplicationThread

2、以bindService方式启动