async.hpp

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#pragma once
 
/// @file userver/engine/async.hpp
/// @brief Low-level TaskWithResult creation helpers
 
#include <userver/engine/deadline.hpp>
#include <userver/engine/impl/task_context_factory.hpp>
#include <userver/engine/task/shared_task_with_result.hpp>
#include <userver/engine/task/task_processor_fwd.hpp>
#include <userver/engine/task/task_with_result.hpp>
#include <userver/utils/impl/wrapped_call.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace engine {
 
namespace impl {
 
template <template <typename> typename TaskType, typename Function, typename... Args>
[[nodiscard]] auto MakeTaskWithResult(
    TaskProcessor& task_processor,
    Task::Importance importance,
    Deadline deadline,
    Function&& f,
    Args&&... args
) {
    using ResultType = typename utils::impl::WrappedCallImplType<Function, Args...>::ResultType;
    constexpr auto kWaitMode = TaskType<ResultType>::kWaitMode;
 
    return TaskType<ResultType>{MakeTask(
        {task_processor, importance, kWaitMode, deadline},
        std::forward<Function>(f),
        std::forward<Args>(args)...
    )};
}
 
}  // namespace impl
 
/// @brief Runs an asynchronous function call using the specified task processor.
///
/// @warning If any logs are written in the task function (outside any manual tracing::Span scopes),
/// then those logs will have no `span_id` (yikes!).
/// If you create a span there manually, it will be disconnected from the outside trace.
/// **Prefer utils::Async by default instead.**
///
/// @warning To hide a spammy span from traces, use @ref tracing::Span::CurrentSpan plus
/// @ref tracing::Span::SetLogLevel instead.
/// Logs will then be linked to the nearest span that is written out.
///
/// @warning Some clients may call tracing::Span::CurrentSpan unconditionally, so don't be too surprised
/// if they won't work without a span scope. Do write tests.
///
/// `AsyncNoSpan` is useful for:
/// * implementing periodic tasks (like utils::PeriodicTask);
/// * worker tasks that typically run until service shutdown, and it makes no sense to have a span for the task itself;
/// * some low-level (e.g. driver or filesystem-IO) code where logs are definitely not written;
/// * breaking traces e.g. this is (rarely) wanted for some background tasks.
///
/// @see utils::Async for main documentation on `Async` function family.
template <typename Function, typename... Args>
[[nodiscard]] auto AsyncNoSpan(TaskProcessor& task_processor, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<TaskWithResult>(
        task_processor,
        Task::Importance::kNormal,
        {},
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto SharedAsyncNoSpan(TaskProcessor& task_processor, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<SharedTaskWithResult>(
        task_processor,
        Task::Importance::kNormal,
        {},
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto AsyncNoSpan(TaskProcessor& task_processor, Deadline deadline, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<TaskWithResult>(
        task_processor,
        Task::Importance::kNormal,
        deadline,
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto SharedAsyncNoSpan(TaskProcessor& task_processor, Deadline deadline, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<SharedTaskWithResult>(
        task_processor,
        Task::Importance::kNormal,
        deadline,
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto AsyncNoSpan(Function&& f, Args&&... args) {
    return AsyncNoSpan(current_task::GetTaskProcessor(), std::forward<Function>(f), std::forward<Args>(args)...);
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto SharedAsyncNoSpan(Function&& f, Args&&... args) {
    return SharedAsyncNoSpan(current_task::GetTaskProcessor(), std::forward<Function>(f), std::forward<Args>(args)...);
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto AsyncNoSpan(Deadline deadline, Function&& f, Args&&... args) {
    return AsyncNoSpan(
        current_task::GetTaskProcessor(),
        deadline,
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
template <typename Function, typename... Args>
[[nodiscard]] auto SharedAsyncNoSpan(Deadline deadline, Function&& f, Args&&... args) {
    return SharedAsyncNoSpan(
        current_task::GetTaskProcessor(),
        deadline,
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
/// @see Task::Importance::Critical
template <typename Function, typename... Args>
[[nodiscard]] auto CriticalAsyncNoSpan(TaskProcessor& task_processor, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<TaskWithResult>(
        task_processor,
        Task::Importance::kCritical,
        {},
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
/// @see Task::Importance::Critical
template <typename Function, typename... Args>
[[nodiscard]] auto SharedCriticalAsyncNoSpan(TaskProcessor& task_processor, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<SharedTaskWithResult>(
        task_processor,
        Task::Importance::kCritical,
        {},
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
/// @see Task::Importance::Critical
template <typename Function, typename... Args>
[[nodiscard]] auto CriticalAsyncNoSpan(Function&& f, Args&&... args) {
    return CriticalAsyncNoSpan(
        current_task::GetTaskProcessor(),
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
/// @see Task::Importance::Critical
template <typename Function, typename... Args>
[[nodiscard]] auto SharedCriticalAsyncNoSpan(Function&& f, Args&&... args) {
    return SharedCriticalAsyncNoSpan(
        current_task::GetTaskProcessor(),
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
/// @overload
/// @see Task::Importance::Critical
template <typename Function, typename... Args>
[[nodiscard]] auto CriticalAsyncNoSpan(Deadline deadline, Function&& f, Args&&... args) {
    return impl::MakeTaskWithResult<TaskWithResult>(
        current_task::GetTaskProcessor(),
        Task::Importance::kCritical,
        deadline,
        std::forward<Function>(f),
        std::forward<Args>(args)...
    );
}
 
}  // namespace engine
 
USERVER_NAMESPACE_END