deadline_timer.h File Reference

Atomic absolute-deadline timer used for lock-free timeout tracking on hot paths. More...

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

Include dependency graph for deadline_timer.h:

Go to the source code of this file.

Classes
class	vlink::DeadlineTimer
	Cache-line aligned atomic deadline counter with millisecond / microsecond / nanosecond precision. More...

Namespaces
	vlink

Detailed Description

Atomic absolute-deadline timer used for lock-free timeout tracking on hot paths.

DeadlineTimer stores a single absolute monotonic timestamp inside a 64-bit atomic, which makes deadline checks branch-light and concurrent reads safe without external locking. It is used inside connection bookkeeping and RPC request tracking to detect expired operations.

State diagram

*   +--------+ set_deadline / set_deadline_abs +---------+ now >= deadline +----------+
*   |  idle  | ------------------------------> |  armed  | --------------> | expired  |
*   | (zero) |                                 |         |                 +----------+
*   +--------+ <------- reset() --------------- +---------+                       |
*      ^                                                                          |
*      +-----------------------  reset() / set 0 --------------------------------+
* 

Comparison vs the periodic vlink::Timer

Aspect	vlink::DeadlineTimer	vlink::Timer
Purpose	Track a single deadline	Schedule repeating callbacks
Backing storage	One atomic<uint64_t>	Loop-managed timer list
Owns a thread	No	Owned by an attached MessageLoop
Cost per check	One atomic load	Insertion / removal on the loop
Cancellation	reset()	detach() on the timer instance

Example

vlink::DeadlineTimer t(200);                          // 200 ms from now
while (!t.has_expired()) {
  process_events();
}
const int64_t left = t.remaining_time();              // 0 once past deadline
 
const uint64_t now = vlink::ElapsedTimer::get_cpu_timestamp();
t.set_deadline_abs(now + 500);                        // absolute reset