A Just-In-Time (JIT) compiler is a system that improves the performance of software applications by translating bytecode, which is a form of intermediate code, into native machine code at runtime, rather than before the application is executed. This process is known as dynamic compilation or runtime compilation.
In general, a JIT compiler works as part of the runtime environment of a programming language. When a program is executed, the runtime environment uses the JIT compiler to convert the bytecode into machine code for the processor to execute. This conversion happens on-the-fly, for the parts of the code that are currently being executed, which is why it's called "just-in-time" compilation.
The JIT compiler optimizes the code based on current execution conditions, which can lead to more efficient execution than static compilation, where code is compiled before execution and without knowledge of the runtime environment. By compiling at runtime, the JIT can make use of specific information about the hardware it's running on, allowing for optimizations that are not possible at compile-time.
The JIT compilation process typically involves several steps:
Monitoring: The runtime environment monitors which parts of the code are frequently executed and therefore would benefit from compilation.
Compilation: The identified bytecode is compiled into machine code by the JIT compiler.
Execution: The machine code is executed directly by the system's processor.
Caching: The compiled machine code is often cached so that it can be reused without recompilation when the same code is executed again.
