gecko/embedding/android/MemoryWatcher.java

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package org.mozilla.gecko;

import android.os.*;
import android.app.*;
import android.app.ActivityManager.*;
import android.util.*;


// Memory Watcher
//
// the onLowMemory method is not called on the foreground
// activity.  Hence we need something that monitors memory
// growth, and broadcasts onLowMemory when we get low on
// resources.  We can also use this to test to see if the
// system is responsive.  For example, if a call to get
// available memory takes too much time, we can assume that
// the system is unstable and we should try our best to reduce
// resources.  Much of this is a hack and should only be used
// on devices that don't kill us during low memory.  Forgive
// me.

public class MemoryWatcher extends Handler
{
    private static final long MEMORY_WATCHER_INTERVAL = 2000;
    private static final long MEMORY_WATCHER_INTERVAL_DELAY_FACTOR = 5;
    private static final long MEMORY_WATCHER_CRITICAL_RESPONSE_THRESHOLD = 200; // in ms

    private Handler mMemoryWatcherHandler;
    private ActivityManager mActivityManager;
    private MemoryInfo mMemoryInfo;
    private boolean mMemoryWatcherKeepGoing;
    private boolean mMemoryWatcherEnabled = false;

    public MemoryWatcher(GeckoApp app) {
        if (android.os.Build.MODEL.equals("Nexus S") == false)
            return;
        mMemoryWatcherEnabled = true;

        mMemoryWatcherKeepGoing = true;
        mMemoryInfo = new MemoryInfo();
        mActivityManager = (ActivityManager) app.getSystemService("activity");
    }


    @Override
    public void handleMessage(Message msg) {
        long startTime = System.currentTimeMillis();
        mActivityManager.getMemoryInfo(mMemoryInfo);
        long took = System.currentTimeMillis() - startTime;

        /*
          Log.w("GeckoApp", String.format("OOM_CHECKER %d %d %b %s\n",
          mMemoryInfo.availMem,
          mMemoryInfo.threshold,
          mMemoryInfo.lowMemory,
          ("took " + took + "ms")));
        */

        // We will adjust the next time this is called if
        // we fire a memory event.
        long nextInterval = MEMORY_WATCHER_INTERVAL;

        // if this call too long, something is very
        // wrong with the device.  fire a critical
        // notification and hope things get better.
        if (took > MEMORY_WATCHER_CRITICAL_RESPONSE_THRESHOLD) {
            GeckoAppShell.onCriticalOOM();
            nextInterval *= MEMORY_WATCHER_INTERVAL_DELAY_FACTOR;
        }
        else if (mMemoryInfo.lowMemory) {
            GeckoAppShell.onLowMemory();
            nextInterval *= MEMORY_WATCHER_INTERVAL_DELAY_FACTOR;
        }

        if (mMemoryWatcherKeepGoing == true)
            this.sendEmptyMessageDelayed(0, nextInterval);
    }

    public void StartMemoryWatcher() {
        if (mMemoryWatcherEnabled == false)
            return;
        mMemoryWatcherKeepGoing = true;
        sendEmptyMessageDelayed(0, MEMORY_WATCHER_INTERVAL);
    }

    public void StopMemoryWatcher() {
        if (mMemoryWatcherEnabled == false)
            return;
        mMemoryWatcherKeepGoing = false;
        removeMessages(0);
    }
}