In the past, I wanted people to agree with me and so I’d prioritize my fear of rejection over the truth. Eventually I fo

$ for i in `seq 1 100` > do > adb shell am force-stop com.android.samples.mytest > sleep 1 > adb shell am start-activity -W -n com.android.samples.mytest/.MainActivity | grep 'TotalTime' | cut -d -f 2 > done

Tapping on an app icon to launch it many times in a row is… pretty tedious. And doing so in a predictable and consistent way (to avoid introducing variability, like if you happened to launch another app by mistake, or otherwise made the system do extra work throwing off timing results) can be a problem.

But much of the process of application startup happens, by definition, before the system gets around to calling your code. So how do you figure out how long it took to get there?

As I wrote before in an earlier (and unfortunately outdated and incorrect) blog, there’s a handy log that the system has been issuing since the KitKat release. Whenever an activity starts, you’ll see something like this in the logcat output:

So what I really wanted was some way to launch the app from the command line. Then I could run that command to do the same thing over and over, and avoid the variability (and tediousness) of manually launching the app by hand.

adb (Android Debug Bridge, a tool probably familiar to anyone who’s read this far) provides just the thing I needed. More specifically, adb shell provides a command-line interface to launch an app: adb shell am start-activity. The command should also block until the app has finished launching, so we’ll use the -W argument as well (this is necessary for the next step, where we’ll tack on a follow-up command to kill the app post-launch). Here’s the complete launch command:

This Displayed duration does not necessarily include everything your app needs to do before it’s ready to go. You can supply that extra information to the system by calling Activity.reportFullyDrawn() whenever your app determines it’s completely done loading and initializing. If/when you call that optional method, the system issues another log with that timestamp and duration:

This duration (1,380ms in this example) represents the time that it took from launching the app to the time when the system consider it “launched,” which includes drawing the first frame (hence “Displayed”).

In the past, I wanted people to agree with me and so I’d prioritize my fear of rejection over the truth. Eventually I found a better way, and if you follow this guide I’m confident you will too.

I needed to test the startup performance for an app recently (while playing around with the Startup library to see how that affected things — more about that in a future article). And I discovered, like I have on previous strolls down this path, that testing startup performance is… not obvious.

I poked around in logcat, looked at some low-level APIs, and asked some of the engineers on the platform team, and found a few things to help. Better yet, I was able to use facilities in the adb shell tool to completely automate my testing and output information in a way that made it easy to pop the results into a spreadsheet and analyze them.

I wrote this article to explain more about performance, startup testing, and the reasons behind the pieces I used for testing startup. But if you just want something quick here it is:

If you’re testing a piece of runtime code, there are various ways to go about it, from the trivial “write a tight loop and calculate the delta in System.currentTimeMillis()” to something more sophisticated and useful, like the facilities provided by the AndroidX benchmark library.

Performance testing should always involve running a test many times, to reduce the inherent variability in results; the more runs you do, the more faith you can put in the averaged results. I try to run tests a minimum of ten times, but doing even more is even better. Depending on how variable the results are in your situation, and how small the timings are (since variability would have larger impact on smaller durations), doing many more runs might be necessary.

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that no one has ever become great by accident! For this reason, it has long been suggested — success leaves clues. And so, just as Michael Jordan called his repeated failures the key that ultimately unlocked success, Bezos — the “Jordan of Business” — echoed such sentiments: