JIT

Just-In-Time, or JIT, is an acronym that can refer to several concepts, most notably Just-In-Time manufacturing and Just-In-Time compilation.

Just-In-Time manufacturing is a production and inventory strategy that seeks to minimize inventory costs and shorten lead times by ordering and producing only what is needed, when it is needed. Originating in the Toyota Production System, JIT focuses on a pull system, small batch production, and continuous improvement. Core techniques include Kanban signaling, level production, setup time reduction (SMED), and close supplier relationships. Benefits include reduced work-in-progress, lower carrying costs, faster feedback, and higher quality. Risks include supply chain disruption, demand variability, and reliance on reliable suppliers or logistics.

Just-In-Time compilation is a software technique used by many managed and dynamic languages to improve runtime performance. Instead of compiling all code to native instructions ahead of time, a JIT compiler translates bytecode or intermediate representation into native machine code at runtime, often selecting and optimizing hot paths. Benefits include faster execution after warm-up, adaptive optimizations based on actual usage, and reduced initial startup time compared with static compilation. Potential drawbacks include compilation overhead, memory use for the code cache, and complexity. JITs are used in major runtimes such as the Java Virtual Machine and .NET Common Language Runtime, and variants exist in JavaScript engines and other scripting environments. Techniques include method-based, trace-based, and adaptive optimization, with tradeoffs between compilation time and runtime performance.