CLOCKTHREADCPUTIMEID

CLOCK_THREAD_CPUTIME_ID is a clock ID used with POSIX clock APIs to obtain the amount of CPU time consumed by a thread. When passed to clock_gettime, clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) returns a timespec representing the CPU time that the calling thread has spent executing on the processor since the clock started for that thread. This is distinct from wall-clock time; it measures only the time the thread spends running on the CPU and includes time spent in both user mode and kernel mode.

Because it is per-thread, the measurement reflects only the thread's own activity and does not account for time spent by other threads or waiting on I/O. Time the thread is not scheduled, blocked, or waiting does not accumulate. The value increases as the thread executes and is not tied to real time.

Usage notes: This clock is commonly used for profiling, performance tuning, or implementing per-thread quotas. It is typically queried from within the thread itself via clock_gettime. Some environments may support querying another thread, but portability is limited; POSIX APIs typically expose the current thread profile. To compare CPU usage across threads, measure deltas over intervals or across threads you instrument individually.

Availability and portability: CLOCK_THREAD_CPUTIME_ID is supported on Linux with glibc and other POSIX-like systems that expose per-thread CPU time accounting. On systems without this clock, alternatives include CLOCK_PROCESS_CPUTIME_ID or wall-clock measurements; behavior and naming may differ outside Linux.

See also: CLOCK_PROCESS_CPUTIME_ID, clock_gettime, timespec.