java.lang.RuntimeException: WakeLock under-locked C2DM_LIB

Question

I have uploaded my application on google play but users have reported the following exception

java.lang.RuntimeException: WakeLock under-locked C2DM_LIB. This exception occurs when I try to release the WakeLock. Can anyone tell what could be the problem.

Solution 1

I have traced same exception in new GCM Library too. Actually old C2DM Android library have same error, same crash, and Google hasn't fixed it yet. As I can see by our statistics, about 0.1% of users experiencing this crash.

My investigations shows that problem is in incorrect releasing of network WakeLock in GCM library, when library tries to release WakeLock that holds nothing (internal lock counter becomes negative).

I was satisfied with simple solution - just catch this exception and do nothing, because we don't need to do any extra job then our wakelock hold nothing.

In order to do this you need to import GCM library sources in your project, rather than already compiled .jar file. You can find GCM library sources under "$Android_SDK_Home$/extras/google/gcm/gcm-client/src" folder (you need to download it first using Android SDK Manager).

Next open GCMBaseIntentService class, find line

sWakeLock.release();

and surround it with try-catch.

It should look like this:

    synchronized (LOCK) {
        // sanity check for null as this is a public method
        if (sWakeLock != null) {
            Log.v(TAG, "Releasing wakelock");
            try {
                sWakeLock.release();
            } catch (Throwable th) {
                // ignoring this exception, probably wakeLock was already released
            }
        } else {
            // should never happen during normal workflow
            Log.e(TAG, "Wakelock reference is null");
        }
    }

UPDATE: Alternativally, as suggested @fasti in his answer, you can use mWakeLock.isHeld() method to check if wakelock actually holding this lock.

Solution 2

You didn't post your code, so I don't know if you've already done what I will suggest here, but I also had that exception and all I added to fix it was a simple "if" to make sure the WakeLock is actually being held, before trying to release it.

All I added in my onPause was this "if" statement (before the "release()"):

if (mWakeLock.isHeld())
    mWakeLock.release();

and the exception was gone.

Solution 3

Although the isHeld() solution seems nicer, it can actually fail - because it is not atomic (i.e. not thread safe). If you have more than one thread that might release the lock then between the check (isHeld) and the call to relase another thread may release the lock... and then you fail.

By using try/catch you disguise the bug, but in a thread-safe way.

Solution 4

I don't have this problem as long as I don't reinitialize the wake lock and call acquire on the new Object. You should only keep one instance of wakeLock (so make it a field variable). Then you know you're always releasing that one wakeLock.

So....

 if (mWakeLock == null) {
        PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK | PowerManager.ACQUIRE_CAUSES_WAKEUP
                | PowerManager.ON_AFTER_RELEASE, "MyWakeLock");
    }

try{
        mWakeLock.release();//always release before acquiring for safety just in case
    }
    catch(Exception e){
        //probably already released
        Log.e(TAG, e.getMessage());
    }
    mWakeLock.acquire();

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