java – Android(在Scala中)：StackOverflowError取决于何时启动

发布时间：2020-12-15 02:28:47 所属栏目：Java 来源：网络整理

导读：我有这个简单的Activity(在 Scala中,导入ommited)： class TestActivity extends Activity { private val TAG = "TestActivity" private val mHandler = new Handler { override def handleMessage(msg: Message) { Log.d(TAG,"handleMessage") } } private

我有这个简单的Activity(在 Scala中,导入ommited)：

class TestActivity extends Activity {
  private val TAG = "TestActivity"

  private val mHandler = new Handler {
    override def handleMessage(msg: Message) {
      Log.d(TAG,"handleMessage")
    }
  }

  private val mThread = new Thread {
    override def run {
      mHandler.sendEmptyMessage(0)
      Thread.sleep(10)
      run
    }
  }.start

  override def onCreate(savedInstanceState: Bundle) {
    super.onCreate(savedInstanceState)
    setContentView(new TextView(this) {
      setText("hello,world")
    })
  }
}

正如您所看到的,mThread立即启动,运行被尾递归重写,它向mHandler发送一条空消息,短暂休眠并再次发送相同的消息.当活动开始时,我收到此错误：

....
D/TestActivity(28224): handleMessage
D/TestActivity(28224): handleMessage
D/TestActivity(28224): handleMessage
D/TestActivity(28224): handleMessage
I/dalvikvm(28224): threadid=9: stack overflow on call to Landroid/os/MessageQueue;.nativeWake:VI
I/dalvikvm(28224):   method requires 8+20+0=28 bytes,fp is 0x43e33310 (16 left)
I/dalvikvm(28224):   expanding stack end (0x43e33300 to 0x43e33000)
I/dalvikvm(28224): Shrank stack (to 0x43e33300,curFrame is 0x43e35fe0)
W/dalvikvm(28224): threadid=9: thread exiting with uncaught exception (group=0x40015560)

E/AndroidRuntime(28224): FATAL EXCEPTION: Thread-10
E/AndroidRuntime(28224): java.lang.StackOverflowError
E/AndroidRuntime(28224):  at android.os.MessageQueue.enqueueMessage(MessageQueue.java:223)
E/AndroidRuntime(28224):  at android.os.Handler.sendMessageAtTime(Handler.java:457)
E/AndroidRuntime(28224):  at android.os.Handler.sendMessageDelayed(Handler.java:430)
E/AndroidRuntime(28224):  at android.os.Handler.sendEmptyMessageDelayed(Handler.java:394)
E/AndroidRuntime(28224):  at android.os.Handler.sendEmptyMessage(Handler.java:379)
E/AndroidRuntime(28224):  at com.iped.audiotest.MainActivity$$anon$2.run(Activity.scala:20)
E/AndroidRuntime(28224):  at com.iped.audiotest.MainActivity$$anon$2.run(Activity.scala:22)
E/AndroidRuntime(28224):  at com.iped.audiotest.MainActivity$$anon$2.run(Activity.scala:22)
E/AndroidRuntime(28224):  at com.iped.audiotest.MainActivity$$anon$2.run(Activity.scala:22)
...

现在,如果我在创建后不立即启动mThread,就像这样：

private val mThread = new Thread {
    override def run {
      mHandler.sendEmptyMessage(0)
      Thread.sleep(10)
      run
    }
  }

并在触摸事件上触发它,例如：

override def onTouchEvent(event: MotionEvent): Boolean = {
    if (event.getAction == MotionEvent.ACTION_DOWN)
      mThread.start
    true
  }

事情会好的.

我无法解释这一点.

解决方法

所以我做了一些实验,我必须得出结论,如果带有尾递归重写运行的线程在其创建的同一表达式中启动,则尾调用优化将失败(或者是导致错误的任何其他原因) ？)

坏：

class Test {
  val mThread = new Thread {
    override def run {
      println("hello")
      run
    }
  }.start
}

好：

class Test {
  val mThread = new Thread {
    override def run {
      println("hello")
      run
    }
  }
  mThread.start
}

附：我正在运行Scala 2.9.1,但由于库大小较小,因此使用2.8.2进行Android开发.

（编辑：李大同）

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