先上一段代码：

private  IDeviceService deviceService = null;
private ServiceConnection conn=null;
private synchronized void bindyourservice() {    Intent intent = new Intent();intent.setPackage("servicepackagename");intent.setAction("serviceactionname");conn=new ServiceConnection() {@Overridepublic void onServiceConnected(ComponentName componentName, IBinder iBinder) {               deviceService = IDeviceService.Stub.asInterface(iBinder);}@Overridepublic void onServiceDisconnected(ComponentName componentName) {.....................................             }};try {if (bindService(intent, mConn, Service.BIND_AUTO_CREATE)) {...............................} else {....................}} catch (SecurityException e) {.........................}}

这个是最早绑定服务的方式，bindService返回绑定服务状态，访问服务接口需在取到ServiceConnection连接后再访问，整个过程是异步的，而且就算开线程去绑定服务、加锁也没办法在一个方法里面返回这个service对象，原因是这个方法里面的实现：

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

看下这个的代码：

  public boolean bindService(Intent service, ServiceConnection conn, int flags) {warnIfCallingFromSystemProcess();return bindServiceCommon(service, conn, flags, null, mMainThread.getHandler(), null,getUser());}@Overridepublic boolean bindService(Intent service, int flags, Executor executor, ServiceConnection conn) {return bindServiceCommon(service, conn, flags, null, null, executor, getUser());}@Overridepublic boolean bindIsolatedService(Intent service, int flags, String instanceName,Executor executor, ServiceConnection conn) {warnIfCallingFromSystemProcess();if (instanceName == null) {throw new NullPointerException("null instanceName");}return bindServiceCommon(service, conn, flags, instanceName, null, executor, getUser());}@Overridepublic boolean bindServiceAsUser(Intent service, ServiceConnection conn, int flags,UserHandle user) {return bindServiceCommon(service, conn, flags, null, mMainThread.getHandler(), null, user);}/** @hide */@Overridepublic boolean bindServiceAsUser(Intent service, ServiceConnection conn, int flags,Handler handler, UserHandle user) {if (handler == null) {throw new IllegalArgumentException("handler must not be null.");}return bindServiceCommon(service, conn, flags, null, handler, null, user);}.....................private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,String instanceName, Handler handler, Executor executor, UserHandle user) {....................
}

 bindServiceCommon是个私有方法，里面又套了几层代码，太长，翻起来就是整个系统bindservice的流程了。

关键点，bindservice执行的时候接收的Handler是 mMainThread.getHandler()，这个是APP的主线程，也就是无论外部怎么折腾，这个是在主线程接收的。

在上面这段系统代码段里面，有两个方法是可以使用的：

//method 1
public boolean bindService(Intent service, int flags, Executor executor, ServiceConnection conn)
//method 2
/** @hide */
@Override
public boolean bindServiceAsUser(Intent service, ServiceConnection conn, int flags,Handler handler, UserHandle user)

1、bindService

在bindService有一个传参executor，接收ServiceConnection放到了这个里面：

private boolean[] isBind = {false};
private CountDownLatch latch = new CountDownLatch(1);
private boolean bindyourservice(final Context context){if(deviceService==null){latch = new CountDownLatch(1);Executor executor= Executors.newSingleThreadExecutor();executor.execute(new Runnable() {@Overridepublic void run() {mConn=new ServiceConnection() {@Overridepublic void onServiceConnected(ComponentName className, IBinderiBinder) {deviceService = IDeviceService.Stub.asInterface(iBinder);isBind[0] =true;latch.countDown();}@Overridepublic void onServiceDisconnected(ComponentName className) {                          isBind[0] =false;latch.countDown();}};Intent intent = new Intent();intent.setPackage("yourservicename");intent.setAction("yourserviceaction");if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {boolean bind=bindService(intent, Context.BIND_AUTO_CREATE,executor,mConn);if(!bind){                               isBind[0] =false;latch.countDown();}}}});if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT) {                   try {latch.await();} catch (InterruptedException e) {e.printStackTrace();}                   if(!isBind[0])return false;}else{                   return false;}}         return true;}

需要注意的是Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q，这个方法是android7.0及以后提供的。

2、bindServiceAsUser

也可以实现方法1的功能，只不过把接收对象换成了Handler ，bindServiceAsUser是系统隐藏方法，需通过反射方法使用，至于bindServiceAsUser是否早于android7.0之前就有，无法确认。