Summary - Performance

Combine benchmark, Stopwatch and profiling to write a perf tool.

Summary - Performance

In this group we learned Dart's performance tools. benchmark measures code speed; Stopwatch is the built-in timer; ProcessInfo gives memory usage; caching (memoization) speeds up repeated computation; DevTools and Timeline are used for profiling.

In this summary we will write a small program that brings Stopwatch and the cached fib function together. The program starts a Stopwatch, computes cached fib(20), stops the Stopwatch and prints the result. This is a small example of an application's performance layer: measurement + optimization together.

Exercise Stopwatch + memoized fib

Define the map final cache = <int, int>{}; (outside main). Write int fib(int n): if n < 2 return n; if cache.containsKey(n) return cache[n]!; else compute fib(n-1) + fib(n-2), store, return. In main start with final sw = Stopwatch()..start();, call final result = fib(20);, then sw.stop();. Print with print('fib(20): $result') and print('Stopwatch: ${sw.isRunning}').

Show example solution

final cache = <int, int>{};

int fib(int n) {
  if (n < 2) return n;
  if (cache.containsKey(n)) return cache[n]!;
  final r = fib(n - 1) + fib(n - 2);
  cache[n] = r;
  return r;
}

void main() {
  final sw = Stopwatch()..start();
  final result = fib(20);
  sw.stop();
  print('fib(20): $result');
  print('Stopwatch: ${sw.isRunning}');
}

Test yourself

Which class measures time?
- AES
- Stopwatch
- Hmac
- bcrypt
Show answer

Stopwatch — Stopwatch measures time; AES, Hmac or bcrypt are security tools.
Match the performance tools

Stopwatch

Time
fib

Fibonacci
cache

Cache
Timeline

Profile

Stopwatch status

print('Stopwatch: ${sw.____}');

Show answer

print('Stopwatch: ${sw.isRunning}');

Next lesson: Project design

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