#include <userver/engine/task/task_with_result.hpp>

Detailed Description

template<typename T>
class engine::TaskWithResult< T >

Asynchronous task with result

Example usage:

  std::vector<engine::TaskWithResult<int>> tasks;
  tasks.reserve(container.size());
  for (auto value : container) {
    // Creating tasks that will be executed in parallel
    tasks.push_back(utils::Async("some_task", [value = std::move(value)] {
      engine::InterruptibleSleepFor(std::chrono::milliseconds(100));
      return value;
    }));
  }
  // we wait for the completion of tasks and get the results
  std::vector<int> results;
  results.reserve(tasks.size());
  for (auto& task : tasks) {
    // If the task completed with an exception,
    // then Get () will throw an exception
    results.push_back(task.Get());
  }

See also: Synchronization Primitives

Examples: samples/flatbuf_service/flatbuf_service.cpp.

Definition at line 30 of file task_with_result.hpp.

Inheritance diagram for engine::TaskWithResult< T >:

Collaboration diagram for engine::TaskWithResult< T >:

Public Member Functions
	TaskWithResult ()=default
	Default constructor.

	TaskWithResult (const TaskWithResult &)=delete

TaskWithResult &	operator= (const TaskWithResult &)=delete

	TaskWithResult (TaskWithResult &&other) noexcept=default
	Moves the other task into this, leaving the other in an invalid state.

TaskWithResult &	operator= (TaskWithResult &&other) noexcept=default
	If this Task is still valid and is not finished, cancels it and waits until it finishes before moving the other. Otherwise just moves the other task into this, leaving the other in invalid state.

T	Get () noexcept(false)
	Returns (or rethrows) the result of task invocation. After return from this method the task is not valid.

Public Member Functions inherited from engine::Task
	Task ()
	Default constructor.

	~Task ()
	If the task is still valid and is not finished, cancels it and waits until it finishes.

	Task (Task &&other) noexcept
	Moves the other task into this, leaving the other in an invalid state.

Task &	operator= (Task &&other) noexcept
	If this Task is still valid and is not finished, cancels it and waits until it finishes before moving the other. Otherwise just moves the other task into this, leaving the other in invalid state.

	Task (const Task &)=delete

Task &	operator= (const Task &)=delete

void	Detach () &&
	Detaches task, allowing it to continue execution out of scope; memory safety is much better with concurrent::BackgroundTaskStorage.

Public Member Functions inherited from engine::TaskBase
bool	IsValid () const
	Checks whether this object owns an actual task (not `State::kInvalid`)

State	GetState () const
	Gets the task State.

bool	IsFinished () const
	Returns whether the task finished execution.

void	Wait () const noexcept(false)
	Suspends execution until the task finishes or caller is cancelled. Can be called from coroutine context only. For non-coroutine context use BlockingWait().

template<typename Rep , typename Period >
void	WaitFor (const std::chrono::duration< Rep, Period > &) const noexcept(false)
	Suspends execution until the task finishes or after the specified timeout or until caller is cancelled.

template<typename Clock , typename Duration >
void	WaitUntil (const std::chrono::time_point< Clock, Duration > &) const noexcept(false)
	Suspends execution until the task finishes or until the specified time point is reached or until caller is cancelled.

void	WaitUntil (Deadline) const
	Suspends execution until the task finishes or until the specified deadline is reached or until caller is cancelled.

void	RequestCancel ()
	Queues task cancellation request.

void	SyncCancel () noexcept
	Cancels the task and suspends execution until it is finished. Can be called from coroutine context only. For non-coroutine context use RequestCancel() + BlockingWait().

TaskCancellationReason	CancellationReason () const
	Gets task cancellation reason.

void	BlockingWait () const

Additional Inherited Members
Public Types inherited from engine::TaskBase
enum class	Importance { kNormal , kCritical }
	Task importance. More...

enum class	State { kInvalid , kNew , kQueued , kRunning , kSuspended , kCancelled , kCompleted }
	Task state. More...

enum class	WaitMode { kSingleWaiter , kMultipleWaiters }
	Task wait mode. More...

Static Public Member Functions inherited from engine::TaskBase
static const std::string &	GetStateName (State state)

Constructor & Destructor Documentation

◆ TaskWithResult()

template<typename T >

engine::TaskWithResult< T >::TaskWithResult ( )

default

Default constructor.

Creates an invalid task.

Member Function Documentation

◆ Get()

template<typename T >

T engine::TaskWithResult< T >::Get ( )

inline

Returns (or rethrows) the result of task invocation. After return from this method the task is not valid.

Exceptions

WaitInterruptedException	when `current_task::IsCancelRequested()` and no TaskCancellationBlockers are present.
TaskCancelledException	if no result is available because the task was cancelled

Definition at line 55 of file task_with_result.hpp.

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

userver/engine/task/task_with_result.hpp