Profiling
- Dart course
- Advanced
- Lesson 77/83
- 5 min
Learn DevTools profiling.
DevTools and profiling
DevTools is the official profiling and debugging tool for Dart and Flutter. It offers CPU profile, memory timeline, network and widget inspector tabs. It opens with dart devtools and connects to a running app.
To add profile markers from code, use the Timeline class in the dart:developer library. Timeline.startSync('name') starts a section; Timeline.finishSync() closes it. These sections appear as labeled blocks in the DevTools timeline tab; they show how long each piece of code takes. For accurate results, run the app in release mode while profiling.
Marking sections with Timeline
Timeline.startSync('name') starts a profile section. Then the measured code runs. Finally Timeline.finishSync() is called. The section name appears in the DevTools timeline; so you see which operation takes which amount of time.
Example: Timeline.startSync('compute'); var sum = 0; for (var i = 0; i < 100; i++) { sum += i; } Timeline.finishSync();. Here the loop appears as a 'compute' labeled block in the timeline. sum (0+1+...+99 = 4950) is deterministic; it can be printed to confirm the section closed correctly. Every startSync must have a matching finishSync.
Practice Profile with Timeline
Add import 'dart:developer' as developer;. In main call developer.Timeline.startSync('compute'). Write a for loop with var sum = 0;: i from 0 to 99 (exclusive 100), sum += i. Then call developer.Timeline.finishSync(). Print with print('Sum: $sum') and print('Timeline: compute').
Starter code
// import the dart:developer library
void main() {
// start a Timeline section, run a loop, close with finishSync
// print sum and Timeline info
}Sample solution
import 'dart:developer' as developer;
void main() {
developer.Timeline.startSync('compute');
var sum = 0;
for (var i = 0; i < 100; i++) {
sum += i;
}
developer.Timeline.finishSync();
print('Sum: $sum');
print('Timeline: compute');
}Expected output
Sum: 4950 Timeline: compute
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 The dart:developer import
import 'dart:____' as developer;import 'dart:developer' as developer;Explanation: dart:developer is imported with the developer alias.
2 Match the profiling parts
| Term | Meaning |
|---|---|
Timeline |
Profile section |
startSync |
Section start |
finishSync |
Section end |
dart:developer |
Library |
3 What does Timeline.startSync do?
- Starts a profile section Correct answer
- crypto
- Stopwatch
- bcrypt
Explanation: Timeline.startSync starts a profile section.