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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.

Practice 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());.

Starter code

main.dart
void main() {
  // define a RuntimeMode class (name, supportsHotReload; describe)
  // create a RuntimeMode; print describe()
}

Sample solution

main.dart
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());
}

Expected output

JIT: hot reload = true

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 A runtime mode

Question 
final mode = '____';
print(mode);
Answer 
final mode = 'AOT';
print(mode);

Explanation: AOT is the production runtime; it generates code at compile time.

2 Match the runtime features

Term Meaning
AOT Production
JIT Development
Hot reload JIT feature
Fast startup AOT feature

3 In which runtime mode does hot reload work?

  • Only AOT
  • Only native machine
  • Only browser
  • JIT Correct answer

Explanation: hot reload runs in the JIT runtime (runtime compilation).

All lessons in Expert

1 Language design

  1. Dart design
  2. Sound null safety
  3. Type system
  4. Subtyping
  5. Records and patterns
  6. Summary - Language design

2 Compiler internals

  1. Compilation pipeline
  2. AST
  3. Kernel
  4. Code generation
  5. dartaotruntime
  6. Summary - Compiler internals

3 FFI

  1. dart:ffi
  2. DynamicLibrary
  3. Native function
  4. Struct
  5. Pointer
  6. Summary - FFI

4 Native extension

  1. What are extensions?
  2. Extension method
  3. Extension operator
  4. Generic extension
  5. Extension vs subclass
  6. Summary - Native extension

5 Build system

  1. build_runner
  2. Builder
  3. source_gen
  4. Analyzer
  5. Custom lint
  6. Summary - Build system

6 Architecture

  1. Clean architecture
  2. Feature-based
  3. Repository
  4. Dependency injection
  5. SOLID
  6. Summary - Architecture

7 Advanced testing

  1. Integration tests
  2. Property tests
  3. Advanced mocking
  4. Coverage
  5. Golden tests
  6. Summary - Advanced testing

8 Expert final

  1. Project design
  2. FFI
  3. Codegen
  4. Architecture
  5. Putting it together