condition_variable.h File Reference

Monotonic-clock condition variable replacement immune to system clock jumps. More...

#include <condition_variable>

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Namespaces
	vlink

Typedefs
using	vlink::ConditionVariable = std::condition_variable
using	vlink::ConditionVariableAny = std::condition_variable_any
using	vlink::condition_variable = ConditionVariable
using	vlink::condition_variable_any = ConditionVariableAny

Detailed Description

Monotonic-clock condition variable replacement immune to system clock jumps.

Older libstdc++ implementations route every std::condition_variable timed wait through CLOCK_REALTIME, so an NTP step or manual date change can spuriously wake or starve waiters (GCC PR 41861 / DR 887). On POSIX systems this header substitutes a hand-rolled vlink::ConditionVariable backed by a pthread_cond_t configured with pthread_condattr_setclock (..., CLOCK_MONOTONIC). On Windows the bug does not apply and the names alias to the standard library types verbatim.

API surface vs std::condition_variable

Aspect	std::condition_variable	vlink::ConditionVariable
Backing clock	CLOCK_REALTIME (libstdc++)	CLOCK_MONOTONIC via pthread_condattr
Timed waits	Sensitive to wall clock jumps	Immune to wall clock jumps
Copy / move	Deleted	Deleted
Public methods	wait / wait_for / wait_until / notify_*	Same signatures, same return types
Native handle	pthread_cond_t*	pthread_cond_t*

Wait / notify sequence

*   producer thread                consumer thread
*   ---------------                 ---------------
*   lock(mtx)                       lock(mtx)
*   state = ready                   cv.wait(lock, predicate)
*   unlock(mtx)                       releases mtx, blocks
*   cv.notify_one()  ----------->     wakes; reacquires mtx
*                                     re-checks predicate
*                                     returns to caller
* 

Both ConditionVariable and ConditionVariableAny accept any std::chrono clock type; non-steady clock arguments are projected onto steady_clock at entry and re-checked at exit for timeout fidelity. Convenience type aliases vlink::condition_variable and vlink::condition_variable_any are also exposed.

Example

std::mutex mtx;
vlink::ConditionVariable cv;
bool ready = false;
 
// Consumer:
{
  std::unique_lock lock(mtx);
  cv.wait_for(lock, std::chrono::milliseconds(200), [&] { return ready; });
}
 
// Producer:
{
  std::lock_guard lock(mtx);
  ready = true;
}
cv.notify_one();