Stopwatch developed by me is lagging behind other standard stopwatch by 8-10 seconds & increases

Question

I have developed a stopwatch in Android . The stopwatch has the feature of Lap calculation too.

I have started the stopwatch . I tested the stopwatch developed by me with multiple standard stopwatches . The problem is that after 1 minutes , the stopwatch developed keeps lagging behind the other stopwatches & the difference keeps on increasing. I got around 8-10 seconds lagging after the 3 minutes.

The following code I am using:

Two classes I am using , one for the Stopwatch implementation & the other for Stopwatch display

StopwatchImplementation.java

        /** The timer used to implement the Stopwatch logic. */
                private Timer mSWatch = null;
                /**
                     * Starts the Stopwatch.
                     */
                    public void watchStart() {
                        if (mSWatch != null)
                            mSWatch .cancel();
                        mSWatch = new Timer();
                        mSWatch .schedule(new TimerTask() {
                            @Override
                            public void run() {
                                mListener.updateUIThread();
                            }

                        }, 0, 100);

                    }

    /** Runnable The Timer_ tick where the time is updated */
        Runnable Timer_Tick = new Runnable() {
            public void run() {
                updateTime(); // Updates the time , calculates the lap duration
            }
        };


    private int mHours = 0;

    /** The mins. */
    private int mMins = 0;

    /** The secs. */
    private int mSecs = 0;

    /** The fraction of a sec. */
    private int mFSec = 0;

    /** The lap hours. */
    private int mLapHours = 0;

    /** The lap mins. */
    private int mLapMins = 0;

    /** The lap secs. */
    private int mLapSecs = 0;

    /** The lap fraction of sec.... 1/10th of a sec*/
    private int mLapFSec = 0;

public void updateTime() {

        try {

            mLapFSec++;
            if (mLapFSec >= 10) {
                mLapFSec = 0;
                mLapSecs++;
                if (mLapSecs >= 60) {
                    mLapSecs = 0;
                    mLapMins++;
                    if (mLapMins >= 60) {
                        mLapMins = 0;
                        mLapHours++;
                    }
                }
            }

            mFSec++;
            if (mFSec >= 10) {
                mFSec = 0;
                mSecs++;
                if (mSecs >= 60) {
                    mSecs = 0;
                    mMins++;
                    if (mMins >= 60) {
                        mMins = 0;
                        mHours++;
                    }
                }
            }
}

StopwatchScreen.java

StopwatchImplementation mStopWatch = new StopwatchImplementation(this);


/**
     * Update ui thread.
     */
    public void updateUIThread() {

        StopWatchScreen.this.runOnUiThread(mStopWatch.Timer_Tick);
    }

public void startPressed() {


        mStopWatch.watchStart();

    }

Kindly provide any inputs regarding where the calculation is going wrong.

Thanks in advance.

Warm Regards,

CB

Answer 1

You cannot rely on the scheduling of a TimerTask for precision timing. You have asked for the updateTime method to be called every 100 milliseconds, but the Android system will only adhere to this roughly - it might take 99 or 101 milliseconds before the next time updateTime is called. Because of this you should avoid timing mechanisms which rely on simply increasing a counter.

For this reason you should record the start time, then compare the current time to the start time to get the amount of time elapsed. For instance:

private long startTime;

public void watchStart() {
    startTime = SystemClock.elapsedRealtime();
    ...
}

public void updateTime() {
    final long currentTime = SystemClock.elapsedRealtime();
    final long elapsedTime = currentTime - startTime;

    // convert elapsedTime in seconds, minutes etc
    final int seconds = (elapsedTime/1000)%60;
    final int minutes = (elapsedTime/(1000*60))%60;
    final int hours = (elapsedTime/(100*60*60))%24;
    ...
}