ExecutionTime

Execution time, in computing, refers to the amount of time a computer program or operation takes to complete from start to finish. It is commonly distinguished into wall-clock time, the real elapsed time as observed by a clock, and CPU time, the amount of time the processor spends executing the process. In multi-threaded environments, CPU time can sum across threads and may differ from wall-clock time, especially when tasks run concurrently or wait on I/O.

Measurement is carried out with built-in language tools, standard libraries, or external utilities. Examples include Unix time, Windows Performance Monitor, Python's time.perf_counter and time.process_time, Java's System.nanoTime, C++ std::chrono, and profiling tools such as perf, Valgrind, or Visual Studio Profiler. For microbenchmarks, it is common to run many iterations, discard warm-up runs, and report mean and confidence intervals.

Uses and implications: Execution time is a fundamental metric in benchmarking, performance optimization, and capacity planning. It informs algorithm choice, resource provisioning, and the ability to meet real-time constraints. Factors affecting measured execution time include algorithm complexity, language and compiler optimizations, memory access patterns, I/O latency, caching, and system load.

Common pitfalls: measurement bias from caching, JIT compilation, or garbage collection; insufficient sample size; environment variability; non-deterministic operations; and the potential mismatch between measured execution time and real user experience if I/O or interactivity dominates.