cached_timestamp.h File Reference

Sub-second-cached timestamp string generator used by the VLink logger hot path. More...

#include <atomic>
#include <chrono>
#include <cstdint>
#include <mutex>
#include <string_view>
#include "./macros.h"

Include dependency graph for cached_timestamp.h:

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Classes
class	vlink::CachedTimestamp
	Mutable cached generator for short formatted timestamps. More...

Namespaces
	vlink

Detailed Description

Sub-second-cached timestamp string generator used by the VLink logger hot path.

CachedTimestamp renders a wall-clock or UTC timestamp into a stable internal buffer and patches only the millisecond suffix when the seconds field has not advanced. This avoids the repeated snprintf / localtime_r round trip that dominates naive per-line logger output.

Resolution and field layout

Field	Width	Source
Month	2	%02d
Day	2	%02d
Hour	2	%02d
Minute	2	%02d
Second	2	%02d
Millisecond (in-place patch)	3	%03d, last three chars of buffer

The default format "%02d-%02d @c %02d:%02d:%02d.%03d" produces 18 characters such as "03-18 14:30:01.042". The internal buffer is 32 bytes; longer formats are dropped.

Example

vlink::CachedTimestamp ts;
for (int i = 0; i < 1000; ++i) {
  // Wall clock (local time) - patched in place on the same second.
  std::string_view local = ts.get();
  // UTC variant on demand:
  std::string_view utc   = ts.get("%02d-%02d %02d:%02d:%02d.%03d", true);
  write_to_log(local);
}

Note

Used internally by vlink::Logger. Application code rarely needs to construct one directly; doing so is harmless and inexpensive.