Unlike other time metrics that focus only on active work, wall time is the experienced by an observer standing by and watching a physical or digital clock.
1. Definition and Core Concept Wall time (also known as "real time," "elapsed real time," or "wall clock time") is the total time that elapses from the start of a process or event to its end, as measured by a clock on the wall (or, more precisely, by a standard timekeeping device like a wristwatch or system clock). It includes every possible delay, interruption, or idle period that occurs in the real world. wall time
| Language/Environment | Recommended API | Notes | |----------------------|----------------|-------| | | clock_gettime(CLOCK_MONOTONIC, &ts) | Monotonic clock unaffected by NTP adjustments | | Python | time.perf_counter() | High-resolution, monotonic, includes sleep time | | Java | System.nanoTime() | Monotonic, not System.currentTimeMillis() (which is wall-clock time that can jump) | | Go | time.Now() (combined with time.Since(start) ) | On most OSes, uses monotonic clock internally | | Command line (Unix) | time ./program | Reports real (wall) time | | Command line (Windows) | Measure-Command .\program.exe | PowerShell cmdlet | Unlike other time metrics that focus only on
import time start = time.time() # Can go backwards if system clock is adjusted # ... work ... end = time.time() It includes every possible delay, interruption, or idle