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copied!<blockquote> <p>What I am unsure about is the check using <code>isHeld()</code> - does it really tell me if a <code>WakeLock</code> is acquired or not, and do I need to do this check at all?</p> </blockquote> <p>Actually slightly tricky to answer. Looking at the source for <code>PowerManager</code> and <code>PowerManager.WakeLock</code> <a href="https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/core/java/android/os/PowerManager.java" rel="nofollow">here</a> the <code>WakeLock.acquire()</code> and <code>WakeLock.acquireLocked()</code> methods are as follows...</p> <pre><code>public void acquire(long timeout) { synchronized (mToken) { acquireLocked(); mHandler.postDelayed(mReleaser, timeout); } } private void acquireLocked() { if (!mRefCounted || mCount++ == 0) { // Do this even if the wake lock is already thought to be held (mHeld == true) // because non-reference counted wake locks are not always properly released. // For example, the keyguard's wake lock might be forcibly released by the // power manager without the keyguard knowing. A subsequent call to acquire // should immediately acquire the wake lock once again despite never having // been explicitly released by the keyguard. mHandler.removeCallbacks(mReleaser); try { mService.acquireWakeLock(mToken, mFlags, mTag, mWorkSource); } catch (RemoteException e) { } mHeld = true; } } </code></pre> <p>...<code>mService</code> is an <code>IPowerManager</code> interface and the source for it isn't available so it's hard to tell what may or may not go wrong when attempting to call <code>acquireWakeLock(...)</code>.</p> <p>In any case, the only exception that can be caught is <code>RemoteException</code> and the <code>catch</code> block does nothing. Immediately after the try/catch, <code>mHeld</code> is set <code>true</code> regardless.</p> <p>In short, if you call <code>isHeld()</code> immediately after <code>acquire()</code> the result will always be <code>true</code>.</p> <p>Looking further into the source for <code>PowerManager.WakeLock</code> shows similar behaviour for <code>release()</code> which calls <code>release(int flags)</code> where the <code>mHeld</code> member is always set to <code>false</code> regardless of what happens.</p> <p>In conclusion I'd suggest it is always a good idea to check <code>isHeld()</code> just as a best practice in case later versions of Android change this behaviour of the <code>WakeLock</code> methods.</p>

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