engine::PulseEventSubscription Class Reference

#include <userver/engine/pulse_event.hpp>

Detailed Description

A one-shot subscription from PulseEvent::Subscribe.

Satisfies engine::Awaitable, for use with engine::WaitAnyContext and friends.

Note

For simple "subscribe to updates" cases a callback API is often more convenient: concurrent::AsyncEventChannel.

Example. A parent task publishes two atomic config fields and wakes all consumers. Each consumer assembles a Config and passes it to ApplyConfig.

Initialization:

    struct Config {
        int timeout_ms{};
        bool enabled{};
 
        bool operator==(const Config&) const = default;
    };
 
    std::atomic<int> apply_calls{0};
    const auto apply_config = [&apply_calls](const Config& /*config*/) {
        apply_calls.fetch_add(1, std::memory_order_relaxed);
    };
 
    std::atomic<int> timeout_ms{0};
    std::atomic<bool> enabled{false};
    engine::PulseEvent event;

Publisher side:

    timeout_ms.store(100, std::memory_order_relaxed);
    enabled.store(true, std::memory_order_relaxed);
    event.Send();

Consumer side:

            Config last{};
            while (!engine::current_task::ShouldCancel()) {
                auto subscription = event.Subscribe();
                const Config config{
                    .timeout_ms = timeout_ms.load(std::memory_order_relaxed),
                    .enabled = enabled.load(std::memory_order_relaxed),
                };
                if (config != last) {
                    apply_config(config);
                    last = config;
                    continue;
                }
                if (subscription.WaitUntil({}) != engine::FutureStatus::kReady) {
                    break;
                }
            }

Definition at line 41 of file pulse_event.hpp.

Inheritance diagram for engine::PulseEventSubscription:

Public Member Functions
	PulseEventSubscription (const PulseEventSubscription &)=delete
	PulseEventSubscription (PulseEventSubscription &&other) noexcept
PulseEventSubscription &	operator= (const PulseEventSubscription &)=delete
PulseEventSubscription &	operator= (PulseEventSubscription &&other) noexcept
bool	IsValid () const noexcept
bool	IsReady () const noexcept override
FutureStatus	WaitUntil (Deadline)
	Waits until a concurrent PulseEvent::Send satisfies this subscription, or the deadline expires, or the current task is cancelled.
AwaitableToken	GetAwaitableToken () noexcept
	Satisfies engine::Awaitable, for use with engine::WaitAnyContext and friends.

Member Function Documentation

IsReady()

bool engine::PulseEventSubscription::IsReady ( ) const

nodiscardoverridenoexcept

Returns

true if a PulseEvent::Send after this subscription has already happened

IsValid()

bool engine::PulseEventSubscription::IsValid ( ) const

nodiscardnoexcept

Returns

true if this object was issued by PulseEvent::Subscribe

Friends And Related Symbol Documentation

PulseEvent

friend class PulseEvent

friend

Definition at line 64 of file pulse_event.hpp.

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

• userver/engine/pulse_event.hpp