wait_all_checked.hpp

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#pragma once
 
/// @file userver/engine/wait_all_checked.hpp
/// @brief Provides engine::WaitAllChecked
 
#include <chrono>
#include <vector>
 
#include <userver/engine/deadline.hpp>
#include <userver/engine/future_status.hpp>
#include <userver/utils/meta.hpp>
#include <userver/utils/span.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace engine {
 
/// @ingroup userver_concurrency
///
/// @brief Waits for the successful completion of all of the specified tasks
/// or for the cancellation of the caller.
///
/// Effectively performs `for (auto& task : tasks) task.Wait();` with a twist:
/// if any task completes with an exception, it gets rethrown ASAP.
///
/// Invalid tasks are skipped.
///
/// Tasks are not invalidated by `WaitAllChecked`; the result can be retrieved
/// after the call.
///
/// @param tasks either a single container, or a pack of future-like elements.
/// @throws WaitInterruptedException when `current_task::ShouldCancel()` (for
/// WaitAllChecked versions without a deadline)
/// @throws std::exception one of specified tasks exception, if any, in no
/// particular order.
///
/// @note Has overall computational complexity of O(N^2),
/// where N is the number of tasks.
/// @note Keeping the tasks valid may have a small extra memory impact. Make
/// sure to drop the tasks after reading the results.
/// @note Prefer engine::GetAll for tasks without a result, unless you
/// specifically need to keep the tasks alive for some reason.
template <typename... Tasks>
void WaitAllChecked(Tasks&... tasks);
 
/// @ingroup userver_concurrency
///
/// @overload void WaitAllChecked(Tasks&... tasks)
template <typename... Tasks, typename Rep, typename Period>
[[nodiscard]] FutureStatus WaitAllCheckedFor(
    const std::chrono::duration<Rep, Period>& duration, Tasks&... tasks);
 
/// @ingroup userver_concurrency
///
/// @overload void WaitAllChecked(Tasks&... tasks)
template <typename... Tasks, typename Clock, typename Duration>
[[nodiscard]] FutureStatus WaitAllCheckedUntil(
    const std::chrono::time_point<Clock, Duration>& until, Tasks&... tasks);
 
/// @ingroup userver_concurrency
///
/// @overload void WaitAllChecked(Tasks&... tasks)
template <typename... Tasks>
[[nodiscard]] FutureStatus WaitAllCheckedUntil(Deadline deadline,
                                               Tasks&... tasks);
 
namespace impl {
 
class ContextAccessor;
 
FutureStatus DoWaitAllChecked(utils::span<ContextAccessor*> targets,
                              Deadline deadline);
 
template <typename Container>
FutureStatus WaitAllCheckedFromContainer(Deadline deadline, Container& tasks) {
  std::vector<ContextAccessor*> targets;
  targets.reserve(std::size(tasks));
 
  for (auto& task : tasks) {
    targets.push_back(task.TryGetContextAccessor());
  }
 
  return impl::DoWaitAllChecked(targets, deadline);
}
 
template <typename... Tasks>
FutureStatus WaitAllCheckedFromTasks(Deadline deadline, Tasks&... tasks) {
  ContextAccessor* targets[]{tasks.TryGetContextAccessor()...};
  return impl::DoWaitAllChecked(targets, deadline);
}
 
inline FutureStatus WaitAllCheckedFromTasks(Deadline /*deadline*/) {
  return FutureStatus::kReady;
}
 
void HandleWaitAllStatus(FutureStatus status);
 
}  // namespace impl
 
template <typename... Tasks>
void WaitAllChecked(Tasks&... tasks) {
  impl::HandleWaitAllStatus(engine::WaitAllCheckedUntil(Deadline{}, tasks...));
}
 
template <typename... Tasks, typename Rep, typename Period>
[[nodiscard]] FutureStatus WaitAllCheckedFor(
    const std::chrono::duration<Rep, Period>& duration, Tasks&... tasks) {
  return WaitAllCheckedUntil(Deadline::FromDuration(duration), tasks...);
}
 
template <typename... Tasks, typename Clock, typename Duration>
[[nodiscard]] FutureStatus WaitAllCheckedUntil(
    const std::chrono::time_point<Clock, Duration>& until, Tasks&... tasks) {
  return WaitAllCheckedUntil(Deadline::FromTimePoint(until), tasks...);
}
 
template <typename... Tasks>
[[nodiscard]] FutureStatus WaitAllCheckedUntil(Deadline deadline,
                                               Tasks&... tasks) {
  if constexpr (meta::impl::IsSingleRange<Tasks...>()) {
    return impl::WaitAllCheckedFromContainer(deadline, tasks...);
  } else {
    return impl::WaitAllCheckedFromTasks(deadline, tasks...);
  }
}
 
}  // namespace engine
 
USERVER_NAMESPACE_END