首先，完全没必要担心AP休眠会导致收不到消息推送。通讯协议栈运行于BP，一旦收到数据包，BP会将AP唤醒，唤醒的时间足够AP执行代码完成对收到的数据包的处理过程。其它的如Connectivity事件触发时AP同样会被唤醒。那么唯一的问题就是程序如何执行向服务器发送心跳包的逻辑。你显然不能靠AP来做心跳计时。Android提供的Alarm Manager就是来解决这个问题的。Alarm应该是BP计时（或其它某个带石英钟的芯片，不太确定，但绝对不是AP），触发时唤醒AP执行程序代码。那么Wake Lock API有啥用呢？比如心跳包从请求到应答，比如断线重连重新登陆这些关键逻辑的执行过程，就需要Wake Lock来保护。而一旦一个关键逻辑执行成功，就应该立即释放掉Wake Lock了。两次心跳请求间隔5到10分钟，基本不会怎么耗电。除非网络不稳定，频繁断线重连，那种情况办法不多。

      网上有说使用AlarmManager，因为AlarmManager 是Android 系统封装的用于管理 RTC 的模块，RTC (Real Time Clock) 是一个独立的硬件时钟，可以在 CPU 休眠时正常运行，在预设的时间到达时，通过中断唤醒 CPU。

      实验

      后来，本人使用AlarmManager，但是又碰到不准的问题，而且当系统繁忙的时候（比如刚开机前一分钟），更为明显，后来查看官方的API说明。因为我之前使用的方法大致是下面的原理：

If your application has strong ordering requirements there are other APIs that you can use to get the necessary behavior; see setWindow(int, long, long, PendingIntent) andsetExact(int, long, PendingIntent).意思是虽然19（包括）之后可能不准确，但是android保留了两个接口，这两个接口是准确的。本人于是使用了这其中一个。

方法如下    TIP：前提是确保你的API是19的或更高，否则做下判断

public static boolean isKitKatOrLater() {

 return Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR2;

}

然后注册一个广播接收器接收

/**
 * 2014-12-05 BenMin FEIXUN_DESKCLOCK_BENMIN_001
 *     modify PWEUN-4141 to remind the user when the timing is over.
 * 2014-12-17 BenMin FEIXUN_DESKCLOCK_BENMIN_002
 *     modify to ensure the fragment attached to Activity when using getResources() function.
 * 2014-12-26 BenMin FEIXUN_DESKCLOCK_BENMIN_003
 *     modify PLGN-489 to stop the ring when press the back menu.
 */
package com.phicomm.keyer;

import java.util.Timer;
import java.util.TimerTask;

import android.R.integer;
import android.app.AlarmManager;
import android.app.AlertDialog;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.media.MediaPlayer;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.NumberPicker;
import android.widget.NumberPicker.Formatter;
import android.widget.NumberPicker.OnValueChangeListener;
import android.widget.TextView;

import com.phicomm.deskclock.DeskClockFragment;
import com.phicomm.deskclock.FxDeskClock;
import com.phicomm.deskclock.R;

public class FxKeyerFragment extends DeskClockFragment implements
        OnClickListener, Formatter, OnValueChangeListener {

    private NumberPicker keyerHour;
    private NumberPicker keyerMinute;
    private NumberPicker keyerSecond;

    private Button kbtnStart;
    private Button kbtnPause;
    private Button kbtnReset;
    private LinearLayout time;
    private TextView hour;
    private TextView minute;
    private TextView second;
    private int hourtime;
    private int minutetime;
    private int secondtime;
    private Timer timer;
    private TimerTask task; 
    
    private MediaPlayer alarmMusic;
    private AlertDialog dialog = null;
   
    
    private static final int originState = 0;   //original state
    private static final int timerState = 1;    //timer state
    private static final int pauseState = 2;    //pause
    private static final int resetState = 3;    //reset
    private static final int overState = 4;     //over
    
    private int stateNow = originState;

    Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
           
            
            if(msg.what == 1){
                
                if(secondtime > 0) {
                    secondtime --;
                    second.setText(format(secondtime));
                } else if(minutetime > 0) {
                    minutetime --;
                    secondtime = 59;
                    second.setText(format(secondtime));
                    minute.setText(format(minutetime));
                } else if(hourtime > 0) {
                    hourtime --;
                    secondtime = 59;
                    minutetime = 59;
                    second.setText(format(secondtime));
                    minute.setText(format(minutetime));
                    hour.setText(format(hourtime));
                }
                if (hourtime <= 0 && minutetime <= 0 && secondtime <= 0) {
                    
                    startRing();
                }
                
            }
        }
    };

    private AlarmManager mAlarmManager;
    private PendingIntent sendIntent;
    public static String ALARM_KEYER_ACTION = "com.phicomm.keyer.alarm_keyer_action";
    private BroadcastReceiver mBroadcastReceiver;
    private boolean isRing = false;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        mAlarmManager = (AlarmManager) this.getActivity().getSystemService(Context.ALARM_SERVICE);
        Intent intent = new Intent();
        intent.setAction(ALARM_KEYER_ACTION);
        sendIntent = PendingIntent.getBroadcast(getActivity(), 0, intent , PendingIntent.FLAG_UPDATE_CURRENT);
        mBroadcastReceiver = new BroadcastReceiver(){
            @Override
            public void onReceive(Context arg0, Intent arg1) {
                // TODO Auto-generated method stub
                kbtnPause.setEnabled(false);
                
                startRing();
                
            }
        };
        IntentFilter filter = new IntentFilter(ALARM_KEYER_ACTION);
        getActivity().registerReceiver(mBroadcastReceiver, filter );
    }
    
    private void startRing(){
        if (timer != null) {
            timer.cancel();
        }
        stateNow = overState;
        if (isAdded() && isRing == false) {
            kbtnPause.setTextColor(getResources().getColor(R.color.text_summery));
            alarmMusic = MediaPlayer.create(getActivity(), R.raw.in_call_alarm);
            alarmMusic.setLooping(true);
            alarmMusic.start();
            isRing = true;
            AlertDialog.Builder builder = new AlertDialog.Builder(getActivity())
                    .setTitle(R.string.tip)
                    .setMessage(R.string.tip_text)
                    .setPositiveButton(R.string.ok, new DialogInterface.OnClickListener()
                    {

                        @Override
                        public void onClick(DialogInterface arg0, int arg1) {
                            // TODO Auto-generated method stub
                            alarmMusic.stop();
                            alarmMusic.release();
                            alarmMusic = null;
                            isRing = false;
                        }

                    });
            dialog = builder.setCancelable(false).create();
            dialog.show();
            
        }
        mAlarmManager.cancel(sendIntent);
        startTime = 0;
        leftTimeToRun = 0;
        ringTime = 0;
        adjustTime = 0;
        setNumberPicker(0);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        View v = inflater.inflate(R.layout.keyer, container, false);

        keyerHour = (NumberPicker) v.findViewById(R.id.keyer_hour);
        keyerHour.setMinValue(0);
        keyerHour.setMaxValue(23);
        keyerHour.setFormatter(this);
        keyerHour.setOnValueChangedListener(this);
        
        keyerHour.getChildAt(0).setFocusable(false);
        

        keyerMinute = (NumberPicker) v.findViewById(R.id.keyer_minute);
        keyerMinute.setMinValue(0);
        keyerMinute.setMaxValue(59);
        keyerMinute.setFormatter(this);
        keyerMinute.setOnValueChangedListener(this);
        
        keyerMinute.getChildAt(0).setFocusable(false);
       

        keyerSecond = (NumberPicker) v.findViewById(R.id.keyer_second);
        keyerSecond.setMinValue(0);
        keyerSecond.setMaxValue(59);
        keyerSecond.setFormatter(this);
        keyerSecond.setOnValueChangedListener(this);
       
        keyerSecond.getChildAt(0).setFocusable(false);
        

        kbtnStart = (Button) v.findViewById(R.id.kbtnStart);
        kbtnStart.setOnClickListener(this);

        kbtnPause = (Button) v.findViewById(R.id.kbtnPause);
        kbtnPause.setOnClickListener(this);

        kbtnReset = (Button) v.findViewById(R.id.kbtnReset);
        kbtnReset.setOnClickListener(this);

        time = (LinearLayout) v.findViewById(R.id.time);
        hour = (TextView) v.findViewById(R.id.hour);
        minute = (TextView) v.findViewById(R.id.minute);
        second = (TextView) v.findViewById(R.id.second);
        
        TimeAllZero();
        
        return v;
    }

    @Override
    public void onResume() {
        if (getActivity() instanceof FxDeskClock) {
            ((FxDeskClock) getActivity()).registerPageChangedListener(this);
        }

        long now = SystemClock.elapsedRealtime();
        if(now <= ringTime && stateNow == timerState){
            long leftTime = ringTime - now;
            setNumberPicker(leftTime);
        } 
        
        if(stateNow == overState) {
            setNumberPicker(0);
        }
        super.onResume();
    }

    private void setNumberPicker(long leftTime){
        long secs = leftTime/1000;
        int hours = (int) (secs/3600);
        int minutes = (int) ((secs%3600)/60);
        int seconds = (int) ((secs%3600)%60);
        secondtime = seconds;
        minutetime = minutes;
        hourtime = hours;
        second.setText(format(seconds));
        minute.setText(format(minutes));
        hour.setText(format(hours));
        
    }
    @Override
    public void onPause() {
        if (getActivity() instanceof FxDeskClock) {
            ((FxDeskClock) getActivity()).unregisterPageChangedListener(this);
        }
        
        super.onPause();
    }

    public String format(int value) {
        String tmpStr = String.valueOf(value);
        if (value < 10) {
            tmpStr = "0" + tmpStr;
        }
        return tmpStr;
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
        case R.id.kbtnStart:
            
            TimeAllZero();
            
            Start();
            break;
        case R.id.kbtnPause:
            Pause();
            break;
        case R.id.kbtnReset:
            Reset();
            
            kbtnStart.setTextColor(getResources().getColor(R.color.text_summery));
            
            break;
        }
    }

    public void onValueChange(NumberPicker picker, int oldVal, int newVal) {
        if (picker == keyerHour) {
            hourtime = newVal;
        }
        if (picker == keyerMinute) {
            minutetime = newVal;
        }
        if (picker == keyerSecond) {
            secondtime = newVal;
        }
        
        TimeAllZero();
        
    }
    private long startTime = 0;
    private long leftTimeToRun = 0;
    private long ringTime = 0;
    private long adjustTime = 0;
    
    public void Start() {
        
        if (kbtnStart.isEnabled()) {
            kbtnStart.setVisibility(View.GONE);

            time.setVisibility(View.VISIBLE);
            hour.setText(format(hourtime));
            minute.setText(format(minutetime));
            second.setText(format(secondtime));

            kbtnPause.setVisibility(View.VISIBLE);
            kbtnPause.setText(R.string.kpause);
            kbtnPause.setEnabled(true);
            kbtnPause.setTextColor(getResources().getColor(R.color.text_gray));

            kbtnReset.setText(R.string.kreset);
            kbtnReset.setVisibility(View.VISIBLE);

            keyerHour.setVisibility(View.GONE);
            keyerMinute.setVisibility(View.GONE);
            keyerSecond.setVisibility(View.GONE);
            timer = null;
            task = null;
            timer = new Timer();
            task = new TimerTask() {
                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    Message message = new Message();
                    message.what = 1;
                    handler.sendMessage(message);
                }
            };
            timer.schedule(task, 1000, 1000);
            startTime = SystemClock.elapsedRealtime();
            leftTimeToRun = (60 * 60 * hourtime + 60 * minutetime + secondtime) * 1000;
            ringTime = startTime + leftTimeToRun;
            mAlarmManager.cancel(sendIntent);
            if (isKitKatOrLater()) {
                mAlarmManager.setExact(AlarmManager.ELAPSED_REALTIME_WAKEUP, ringTime, sendIntent);
            } else {
                mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, ringTime, sendIntent);
            }
            
            stateNow = timerState;
            
        }
        
    }
    public static boolean isKitKatOrLater() {
        return Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR2;
    }
    
    public void Pause() {
        if(kbtnPause.getText().toString().equals(getResources().getString(R.string.kpause))) {
            kbtnPause.setText(R.string.kcontinue);
            timer.cancel();
            adjustTime = (leftTimeToRun - (SystemClock.elapsedRealtime() - startTime)) % 1000;
            mAlarmManager.cancel(sendIntent);
            stateNow = pauseState;
        } else {
            stateNow = timerState;
            kbtnPause.setText(R.string.kpause);
            secondtime = Integer.parseInt(second.getText().toString());
            minutetime = Integer.parseInt(minute.getText().toString());
            hourtime = Integer.parseInt(hour.getText().toString());
            timer = new Timer();
            task = new TimerTask() {
                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    Message message = new Message();
                    message.what = 1;
                    handler.sendMessage(message);
                }
            };
            timer.schedule(task, adjustTime, 1000);

            startTime = SystemClock.elapsedRealtime();
            leftTimeToRun = (60 * 60 * hourtime + 60 * minutetime + secondtime) * 1000 + adjustTime;
            ringTime = startTime + leftTimeToRun;
            mAlarmManager.cancel(sendIntent);
            if (isKitKatOrLater()) {
                mAlarmManager.setExact(AlarmManager.ELAPSED_REALTIME_WAKEUP, ringTime, sendIntent);
            } else {
                mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, ringTime, sendIntent);
            }
        }
    }
    public void Reset() {
        stateNow = resetState;
        kbtnStart.setVisibility(View.VISIBLE);
        kbtnPause.setVisibility(View.GONE);
        kbtnReset.setVisibility(View.GONE);

        keyerHour.setVisibility(View.VISIBLE);
        keyerHour.setValue(0);
        hourtime = 0;
        keyerMinute.setVisibility(View.VISIBLE);
        keyerMinute.setValue(0);
        minutetime = 0;
        keyerSecond.setVisibility(View.VISIBLE);
        keyerSecond.setValue(0);
        secondtime = 0;

        time.setVisibility(View.GONE);

        timer.cancel();
        
        startTime = 0;
        leftTimeToRun = 0;
        ringTime = 0;
        adjustTime = 0;
        mAlarmManager.cancel(sendIntent);
    }

    public void TimeAllZero() {
        if (keyerHour.getValue() == 0 && keyerMinute.getValue() == 0 && keyerSecond.getValue() == 0) {
            kbtnStart.setEnabled(false);
            kbtnStart.setTextColor(getResources().getColor(R.color.text_summery));
        } else {
            kbtnStart.setEnabled(true);
            kbtnStart.setTextColor(getResources().getColor(R.color.text_gray));
        }
    }

    @Override
    public void onDestroyView() {
        // TODO Auto-generated method stub
        super.onDestroyView();
        if (timer != null) {
            timer.cancel();
            timer = null;
        }
        if (task != null) {
            task = null;
        }

        if (alarmMusic != null) {
            alarmMusic.stop();
            alarmMusic.release();
            alarmMusic = null;

        if(mBroadcastReceiver!= null){
            getActivity().unregisterReceiver(mBroadcastReceiver);
        }
    }

    
}