dartaotruntime

Learn the difference between AOT and JIT runtimes.

dartaotruntime

dartaotruntime is the runtime that runs Dart's AOT (Ahead-Of-Time) compiled programs. In AOT, all code is compiled to machine code at compile time; there is no runtime compilation. This gives fast startup and predictable performance.

The JIT (Just-In-Time) runtime runs on the VM; it compiles code at runtime. JIT provides fast recompilation for the development cycle (hot reload). AOT is used for production, JIT for development.

AOT vs JIT

AOT compiles all code to machine code at compile time; startup is fast, memory footprint is small. Production apps (Flutter release) use AOT. JIT compiles code at runtime; startup is slower but hot reload is possible during development.

JIT collects type feedback inside the VM and optimizes hot paths. AOT does all optimizations upfront via static analysis. Both take Kernel as input but their runtime strategies differ.

Exercise A RuntimeMode class

Define a RuntimeMode class with final String name; final bool supportsHotReload; RuntimeMode(this.name, this.supportsHotReload); field and constructor. Add a String describe() => '$name: hot reload = $supportsHotReload'; method. In main create final r = RuntimeMode('JIT', true);; print with print(r.describe());.

Show example solution

class RuntimeMode {
  final String name;
  final bool supportsHotReload;
  RuntimeMode(this.name, this.supportsHotReload);
  String describe() => '$name: hot reload = $supportsHotReload';
}

void main() {
  final r = RuntimeMode('JIT', true);
  print(r.describe());
}

Test yourself

A runtime mode

final mode = '____';
print(mode);

Show answer

final mode = 'AOT';
print(mode);

Match the runtime features

AOT

Production
JIT

Development
Hot reload

JIT feature
Fast startup

AOT feature
In which runtime mode does hot reload work?
- Only AOT
- Only native machine
- Only browser
- JIT
Show answer

JIT — hot reload runs in the JIT runtime (runtime compilation).

Next lesson: Summary - Compiler internals

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