elapsed_timer.h File Reference

High-resolution elapsed-time measurement with configurable clock source and precision. More...

#include <atomic>
#include <cstdint>
#include "./macros.h"

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Classes
class	vlink::ElapsedTimer
	Atomic, high-resolution elapsed-time timer. More...

Namespaces
namespace	vlink

Detailed Description

High-resolution elapsed-time measurement with configurable clock source and precision.

ElapsedTimer measures how much time (wall-clock or CPU-active time) has elapsed since start() was called. It is the lowest-level timing primitive in VLink and is used internally by DeadlineTimer, CpuProfiler, and the message-loop task latency tracking.

Two independent axes of configuration are available:

Clock source (Method)

Value	Clock source	Notes
kCpuTimestamp	CLOCK_MONOTONIC_RAW / steady_clock	Monotonic wall time, never jumps
kCpuActiveTime	getrusage / GetProcessTimes	CPU user+kernel time consumed

Precision (Accuracy)

Value	Unit	Range (64-bit)
kMilli	milliseconds	~292 million years
kMicro	microseconds	~292 thousand years
kNano	nanoseconds	~292 years

Note

• The timer is not started on construction; call start() explicitly.
• get() returns -1 when the timer has not been started or has been stopped.
• The internal start_time_ is stored as a std::atomic<int64_t>, making concurrent reads from multiple threads safe, though concurrent start()/stop() calls from different threads lead to a data race on the "is started" semantic.
• On Linux, get_sys_timestamp() uses CLOCK_REALTIME via clock_gettime for nanosecond resolution; on Windows it falls back to std::chrono::system_clock.
• get_cpu_timestamp() uses CLOCK_MONOTONIC_RAW on Linux (immune to NTP adjustments) and std::chrono::steady_clock on other platforms.

Example

vlink::ElapsedTimer t(vlink::ElapsedTimer::kCpuTimestamp,
                      vlink::ElapsedTimer::kMicro);
t.start();
do_work();
int64_t us = t.get();   // microseconds elapsed; -1 if not started
t.stop();
 
// One-liner: restart returns elapsed and resets the timer atomically
int64_t delta = t.restart();