LocalTrace

A complete* replacement for all* your android.os.Trace needs.

or

How I Learned To Stop Reading Logs, And Love Visualizations

*: for my purposes

What

A (nearly) drop-in replacement for single-process use of android.os.Trace.beginSection/endSection, but it doesn't have any dependencies (outside of Android API v1).

And look! It gives you this!

How

Sprinkle LocalTrace.beginSection("name") / LocalTrace.endSection() calls around your code (each section MUST begin/end on the same thread), and run the app. Logs are flushed to disk roughly every second, so wait until at least a second after the interesting things have finished. A new file will be created every time your app process starts, so the results won't clobber each other.

Afterward, pull the file via adb pull (or adb shell run-as com.example.yourapp cat file.trace > file.trace for devices where pull doesn't work). Then cat begin_trace.html file.trace end_trace.html > result.html to put the trace output in the middle of the HTML file. (you need to avoid newlines and " in your section names because of this)

Then just open the file in Chrome. It only works in Chrome, unfortunately. Take it up with the systrace team for Android if you find this repugnant, it's not something I can fix :|

Why

Systrace is cool! It gives you a wonderful overview of parallel processes and what they're doing, which can help you diagnose problems like "why is this so damn slow".

But. It requires systrace support on the device, and many manufacturers disable it. And custom tracing sections require API v18+, which are wonderfully useful to see not just "this is doing disk access here", but why it's happening in the first place.

Also but. systrace.py is pretty tightly bound to atrace itself, which means your device has to be plugged in, and it'll end itself after not too long anyway. Yeah, you can feed it a file, but you still need to actually call adb shell atrace -z.

So, while trying to speed things up and find out why it's sometimes slow and sometimes not, and needing to work on Gingerbread devices, I figured out the log format and decided to skip the whole atrace thing. I chopped up the output file from a run, made a logging helper class, and now I can trace every run, every time, and diagnose later when I actually see what I'm looking for.

It has helped immensely.

Save yourself some pain

Both Android Studio and Eclipse support templates that can surround your code. Don't write it all out every time. I use a "Live Template" in Android Studio to save what little sanity I have left:

com.example.LocalTrace.beginSection("$CLASS$ : $METHOD$ ($LINE$)");
try {
$SELECTION$
} finally {
com.example.LocalTrace.endSection();
}

Then simply select the code you want to trace, hit (on a Mac) cmd-opt-T, then t to automagically generate a unique, semi-descriptive named trace section. Sprinkle around your code in interesting areas, see what turns up.

Save even more pain

Combining the output with the begin/end HTML files, and then opening in Chrome, can be a bit of a pain. So I use this:

#!/bin/bash
cat begin_trace.html "$1.trace" end_trace.html > "$1.html" && open -a "Google Chrome.app" "$1.html"

Then, given file.trace, just ./that_script file and voila, you're viewing it.