1page.title=Tracking Memory Allocations 2parent.title=Articles 3parent.link=../browser.html?tag=article 4@jd:body 5 6<p>Writing efficient mobile applications is not always straightforward. In 7particular, Android applications rely on automatic memory management handled by 8Dalvik's garbage collector, which can sometimes cause performance issues if you 9are not careful with memory allocations.</p> 10 11<p>In a performance-sensitive code path, such as the layout or drawing method of 12a view or the logic code of a game, any allocation comes at a price. After too 13many allocations, the garbage collector will kick in and stop your application 14to let it free some memory. Most of the time, garbage collections happen fast 15enough for you not to notice. However, if a collection happens while you are 16scrolling through a list of items or while you are trying to defeat a foe in a 17game, you may suddenly see a drop in performance/responsiveness of the 18application. It's not unusual for a garbage collection to take 100 to 200 ms. 19For comparison, a smooth animation needs to draw each frame in 16 to 33 ms. If 20the animation is suddenly interrupted for 10 frames, you can be certain that 21your users will notice.</p> 22 23<p>Most of the time, garbage collection occurs because of tons of small, 24short-lived objects and some garbage collectors, like generational garbage 25collectors, can optimize the collection of these objects so that the application 26does not get interrupted too often. The Android garbage collector is 27unfortunately not able to perform such optimizations and the creation of 28short-lived objects in performance critical code paths is thus very costly for 29your application.</p> 30 31<p>To help you avoid frequent garbage collections, the Android SDK ships with a 32very useful tool called <em>allocation tracker</em>. This tool is part of DDMS, 33which you must have already used for debugging purposes. To start using the 34allocation tracker, you must first launch the standalone version of DDMS, which 35can be found in the <code>tools/</code> directory of the SDK. The version of 36DDMS included in the Eclipse plugin does not offer you ability to use the 37allocation tracker yet.</p> 38 39<p>Once DDMS is running, simply select your application process and then click 40the <em>Allocation Tracker</em> tab. In the new view, click <em>Start 41Tracking</em> and then use your application to make it execute the code paths 42you want to analyze. When you are ready, click <em>Get Allocations</em>. A list 43of allocated objects will be shown in the first table. By clicking on a line you 44can see, in the second table, the stack trace that led to the allocation. Not 45only you will know what type of object was allocated, but also in which thread, 46in which class, in which file and at which line. The following screenshot shows 47the allocations performed by <a 48href="http://code.google.com/p/shelves">Shelves</a> while scrolling a 49ListView.</p> 50 51<a href="images/ddms_allocation_trackerl.png"> 52 53<img style="cursor:hand;width: 320px; height: 250px;" src="images/ddms_allocation_tracker.png" border="0" alt="" /> 54</a> 55 56<p>Even though it is not necessary — and sometimes not possible — to 57remove all allocations for your performance critical code paths. the allocation 58tracker will help you identify important issues in your code. For instance, a 59common mistake I have seen in many applications is to create a new 60<code>Paint</code> object on every draw. Moving the paint into an instance field 61is a simple fix that helps performance a lot. I highly encourage you to peruse 62the <a href="http://source.android.com/">Android source code</a> to see how we 63reduce allocations in performance-critical code paths. You will also thus 64discover the APIs Android provide to help you reuse objects.</p> 65
