JITcompiling

JITcompiling, or Just-In-Time compiling, is a method of program execution where code is compiled at runtime, rather than before execution. This differs from traditional ahead-of-time (AOT) compilation, where the entire program is translated into machine code before it is run. JITcompiling combines aspects of both interpretation and AOT compilation.

In a JITcompiling system, source code or an intermediate representation (like bytecode) is initially interpreted. As the program runs, frequently executed sections of code are identified. These sections are then compiled into native machine code by the JITcompiler. This compiled native code is then cached and used for subsequent executions of the same code sections, significantly improving performance.

The primary advantage of JITcompiling is its ability to achieve performance close to AOT compiled code while retaining some of the flexibility of interpreters. It can adapt to runtime conditions, potentially optimizing code based on the specific hardware it's running on or the actual data the program is processing. This dynamic optimization can lead to better performance than static AOT compilation in certain scenarios.

However, JITcompiling introduces an initial overhead. The process of identifying, compiling, and caching code takes time during program execution, which can make the startup phase slower compared to interpreted code or AOT compiled code. Despite this, for long-running applications or those with performance-critical loops, the benefits of JITcompiling often outweigh the initial cost. Many modern programming languages and virtual machines, such as Java (JVM) and JavaScript engines, utilize JITcompiling techniques.