UE::TEventCount< CounterType > Class Template Reference

#include <EventCount.h>

Public Member Functions
constexpr	TEventCount ()=default
	TEventCount (const TEventCount &)=delete
TEventCount &	operator= (const TEventCount &)=delete
TEventCountToken< CounterType >	PrepareWait ()
void	Wait (TEventCountToken< CounterType > Compare)
bool	WaitFor (TEventCountToken< CounterType > Compare, FMonotonicTimeSpan WaitTime)
bool	WaitUntil (TEventCountToken< CounterType > Compare, FMonotonicTimePoint WaitTime)
void	Notify ()
void	NotifyWeak ()

Detailed Description

template<typename CounterType>
class UE::TEventCount< CounterType >

A type of event that avoids missed notifications by maintaining a notification count.

This type of event is suited to waiting on another thread conditionally. Typical usage looks similar to this example:

FEventCount Event;
std::atomic<uint32> CurrentValue = 0;

On the waiting thread:

FEventCountToken Token = Event.PrepareWait();
if (CurrentValue < TargetValue)
{
    Event.Wait(Token);
}

On the notifying thread:

if (++CurrentValue == TargetValue)
{
    Event.Notify();
}

Acquiring a token before checking the condition avoids a race because Wait returns immediately when the token no longer matches the notification count.

Constructor & Destructor Documentation

TEventCount() [1/2]

template<typename CounterType >

constexpr UE::TEventCount< CounterType >::TEventCount ( )

constexprdefault

TEventCount() [2/2]

template<typename CounterType >

UE::TEventCount< CounterType >::TEventCount ( const TEventCount< CounterType > &  )

delete

Member Function Documentation

Notify()

template<typename CounterType >

void UE::TEventCount< CounterType >::Notify ( )

inline

Notifies all waiting threads.

Any threads that have called PrepareWait() and not yet waited will be notified immediately if they do wait on a token from a call to PrepareWait() that preceded this call.

NotifyWeak()

template<typename CounterType >

void UE::TEventCount< CounterType >::NotifyWeak ( )

inline

Notifies all waiting threads.

Any threads that have called PrepareWait() and not yet waited will be notified immediately if they do wait on a token from a call to PrepareWait() that preceded this call. Note: This version doesn't provide a memory barrier, you are responsible for the memory ordering for the value you're synchronizing this eventcount with.

operator=()

template<typename CounterType >

TEventCount & UE::TEventCount< CounterType >::operator= ( const TEventCount< CounterType > &  )

delete

PrepareWait()

template<typename CounterType >

TEventCountToken< CounterType > UE::TEventCount< CounterType >::PrepareWait ( )

inline

Prepare to wait.

Call this before any logic that must re-execute if the event is notified in the meantime.

Returns

A token to pass to one of the wait functions to abort the wait if the event has been notified since.

Wait()

template<typename CounterType >

void UE::TEventCount< CounterType >::Wait ( TEventCountToken< CounterType >  Compare )

inline

Wait until the event is notified. Returns immediately if notified since the token was acquired.

Parameters

Compare

A token acquired from PrepareWait() before checking the conditions for this wait.

WaitFor()

template<typename CounterType >

bool UE::TEventCount< CounterType >::WaitFor ( TEventCountToken< CounterType >  Compare, FMonotonicTimeSpan  WaitTime  )

inline

Wait until the event is notified. Returns immediately if notified since the token was acquired.

Parameters

Compare	A token acquired from PrepareWait() before checking the conditions for this wait.
WaitTime	Relative time after which waiting is automatically canceled and the thread wakes.

Returns

True if the event was notified before the wait time elapsed, otherwise false.

WaitUntil()

template<typename CounterType >

bool UE::TEventCount< CounterType >::WaitUntil ( TEventCountToken< CounterType >  Compare, FMonotonicTimePoint  WaitTime  )

inline

Wait until the event is notified. Returns immediately if notified since the token was acquired.

Parameters

Compare	A token acquired from PrepareWait() before checking the conditions for this wait.
WaitTime	Absolute time after which waiting is automatically canceled and the thread wakes.

Returns

True if the event was notified before the wait time elapsed, otherwise false.

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The documentation for this class was generated from the following file:

• Engine/Source/Runtime/Core/Public/Async/EventCount.h