Programming/Time/Run

• Runtime

  • Also known as: run-time, runtime execution, execution time
  • The phase when a program is actually executing, after compilation
  • Operations and evaluations that occur while the program is running

  • Definition

    • The period during which a compiled program executes
    • The execution environment where program code runs
    • Dynamic behavior that cannot be determined until the program runs

  • Key Characteristics

    • Dynamic Execution: Code is executed with actual data and user input
    • Runtime Environment: The system that executes the program (virtual machine, interpreter, or native execution)
    • Dynamic Behavior: Values and control flow determined by runtime conditions
    • Error Handling: Runtime errors occur during execution

  • Runtime Operations

    • Program Execution

      • Instruction execution
      • Memory allocation and deallocation
      • Function calls and stack management

    • Dynamic Behavior

      • User input processing
      • Network requests
      • File I/O operations
      • Database queries

    • Runtime Checks

      • Array bounds checking (in some languages)
      • Null pointer checks
      • Type checks (in dynamically typed languages)
      • Resource availability checks

    • Memory Management

      • Heap allocation
      • Garbage collection (in managed languages)
      • Stack management

  • Runtime vs Compile-Time

    • Runtime: Dynamic behavior, user interaction, actual execution
    • Compile-Time: Static analysis, type checking, constant evaluation
    • Some languages (like Python, JavaScript) have minimal compile-time checks

  • Runtime Environments

    • Virtual Machines

      • JVM (Java Virtual Machine)
      • .NET CLR (Common Language Runtime)
      • Erlang BEAM

    • Interpreters

      • Python interpreter
      • JavaScript engines (V8, SpiderMonkey)

    • Native Execution

      • Compiled languages that run directly on hardware
      • Rust, C, C++, Go (when compiled to native code)

  • Runtime Errors

    • Errors that occur during program execution
    • Examples:
      • Null pointer exceptions
      • Array index out of bounds
      • Division by zero
      • File not found
      • Network timeouts
    • Contrast with compile-time errors, which prevent the program from being built

  • Language Examples

    • Dynamically Typed Languages

      • Python, JavaScript, Ruby: Most type checking happens at runtime
      • Type errors only discovered when code executes

    • Statically Typed Languages

      • Rust, Java, C#: Most type checking at compile-time
      • Runtime errors typically from logic errors or resource issues

  • Benefits and Trade-offs

    • Flexibility: Can handle dynamic data and user input
    • Runtime Optimization: Just-in-time (JIT) compilation can optimize hot paths
    • Error Discovery: Some errors only appear at runtime
    • Performance Overhead: Runtime checks add execution overhead

  • Related

    • Programming/Time/Compile - The compilation phase before execution
    • Runtime environments and virtual machines
    • Dynamic typing vs static typing