start called in an invalid state: 16; at android.media.MediaRecorder.start(Native Method)

public void startRecording(String outputPath) {
    if (recorder == null) {
        recorder = new MediaRecorder();
        recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        recorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
        recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
        recorder.setAudioSamplingRate(RECORDER_SAMPLERATE_22050);
        recorder.setOutputFile(outputPath);
        try {
            recorder.prepare();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    recorder.start();
    SampleRecordThread thread = new SampleRecordThread(outputPath);
    thread.start();

}

private class SampleRecordThread extends Thread {
    private volatile boolean running = true;

    public void exit() {
        running = false;
    }

    @Override
public void run() {
    while (running) {
        try {
            Thread.sleep(10 * 1000);//to record 10 seconds sound
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        recorder.stop();
        recorder.reset();
        recorder.release();
        recorder = null;

        // upload the data to cloud
        if (isWifiActive && isInstallationSaved) {
                    .....
                    record.saveInBackground();
            }

        break;
    }
}

public class AudioRecordManager {

public interface OnAudioRecordCallback {

    void onComplete(String path);

    void onFailed(int code);

}

private OnAudioRecordCallback onAudioRecordCallback;

public void setOnAudioRecordCallback(OnAudioRecordCallback onAudioRecordCallback) {
    this.onAudioRecordCallback = onAudioRecordCallback;
}

private MediaRecorder myRecorder;
private String outputFile;
private AudioRecordThread audioRecordThread;

public AudioRecordManager() {
    audioRecordThread = new AudioRecordThread();
}

private AudioRecordThread audioRecordThread;

public void startRecord() {
    if(audioRecordThread == null || !audioRecordThread.isRunning()){
        new Thread(audioRecordThread).start();
    }
}

public void stopRecord() {
    if(audioRecordThread!=null && audioRecordThread.isRunning()) {
        audioRecordThread.stopRecording();
    }
}

class AudioRecordThread implements Runnable {

    private boolean isRunning;

    private boolean isStop;

    private long startTime;

    private void startRecord() {
        isRunning = true;
        isStop = false;
        File folder = new File(Content.AUDIO_DIR);
        if (!folder.exists()) {
            boolean b = folder.mkdirs();
        }
        startTime = System.currentTimeMillis();
        outputFile = folder.getPath() + "/rec_" + startTime + ".mp3";

        myRecorder = new MediaRecorder();
        myRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        myRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
        myRecorder.setAudioEncoder(MediaRecorder.OutputFormat.AMR_NB);
        myRecorder.setOutputFile(outputFile);
        try {
            myRecorder.prepare();
            myRecorder.start();

            startTime = System.currentTimeMillis();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void stopRecord() {

        final long stopTime = System.currentTimeMillis();

        try {
            if(System.currentTimeMillis() - startTime < 500){
                try{
                    Thread.sleep(500);
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
            myRecorder.stop();

            myRecorder.release();
            myRecorder = null;
        } catch (Exception e) {
            myRecorder = null;
            e.printStackTrace();
        }

        if (stopTime - startTime > 1000) {
            if (onAudioRecordCallback != null) {
                onAudioRecordCallback.onComplete(outputFile);
            }
        } else {
            File current = new File(outputFile);
            current.delete();
            if (onAudioRecordCallback != null) {
                onAudioRecordCallback.onFailed(2);
            }
        }

        isRunning = false;
    }

    @Override
    public void run() {
        startRecord();
        while (!isStop) {
            try {
                Thread.sleep(30);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        stopRecord();
    }

    public void stopRecording() {
        isStop = true;
    }

    public boolean isRunning() {
        return isRunning;
    }
  }
}