engine::SharedTaskWithResult< T > Class Template Reference

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

Detailed Description

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

Asynchronous task with result that has a shared ownership of payload.

Example usage:

  // Creating task that will be awaited in parallel
  auto shared_task = utils::SharedAsync("shared_task", []() {
    engine::InterruptibleSleepFor(std::chrono::milliseconds(100));
 
    return 1;
  });
 
  std::vector<engine::TaskWithResult<void>> tasks;
  std::atomic_int sum{0};
  for (size_t i = 0; i < 4; ++i) {
    // Getting shared_task's result in parallel
    tasks.push_back(
        utils::Async("waiter_task", [shared_task /* copy is allowed */,
                                     &sum]() { sum += shared_task.Get(); }));
  }
 
  for (auto& task : tasks) task.Wait();

See also

Synchronization Primitives

Definition at line 35 of file shared_task_with_result.hpp.

Inheritance diagram for engine::SharedTaskWithResult< T >:

Collaboration diagram for engine::SharedTaskWithResult< T >:

Public Member Functions
	SharedTaskWithResult ()=default
	Default constructor.
	~SharedTaskWithResult ()=default
	If the task is still valid and is not finished and this is the last shared owner of the payload, cancels the task and waits until it finishes.
	SharedTaskWithResult (const SharedTaskWithResult &other)=default
	Assigns the other task into this.
SharedTaskWithResult &	operator= (const SharedTaskWithResult &other)=default
	If this task is still valid and is not finished and other task is not the same task as this and this is the last shared owner of the payload, cancels the task and waits until it finishes before assigning the other. Otherwise just assigns the other task into this.
	SharedTaskWithResult (SharedTaskWithResult &&other) noexcept=default
	Moves the other task into this, leaving the other in an invalid state.
SharedTaskWithResult &	operator= (SharedTaskWithResult &&other) noexcept=default
	If this task is still valid and is not finished and other task is not the same task as this and this is the last shared owner of the payload, cancels the task and waits until it finishes before move assigning the other. Otherwise just move assigns the other task into this, leaving the other in an invalid state.
decltype(auto)	Get () const &noexcept(false)
	Returns (or rethrows) the result of task invocation. Task remains valid after return from this method, thread(coro)-safe.
std::add_lvalue_reference< const T >	Get () &&
Public Member Functions inherited from engine::SharedTask
	SharedTask ()
	Default constructor.
	~SharedTask ()
	If the task is still valid and is not finished and this is the last shared owner of the payload, cancels the task and waits until it finishes.
	SharedTask (const SharedTask &other) noexcept
	Assigns the other task into this.
SharedTask &	operator= (const SharedTask &other) noexcept
	If this task is still valid and is not finished and other task is not the same task as this and this is the last shared owner of the payload, cancels the task and waits until it finishes before assigning the other. Otherwise just assigns the other task into this.
	SharedTask (SharedTask &&other) noexcept
	Moves the other task into this, leaving the other in an invalid state.
SharedTask &	operator= (SharedTask &&other) noexcept
	If this task is still valid and is not finished and other task is not the same task as this and this is the last shared owner of the payload, cancels the task and waits until it finishes before move assigning the other. Otherwise just move assigns the other task into this, leaving the other in an invalid state.
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

SharedTaskWithResult()

template<typename T >

engine::SharedTaskWithResult< T >::SharedTaskWithResult ( )

default

Default constructor.

Creates an invalid task.

Member Function Documentation

Get() [1/2]

template<typename T >

std::add_lvalue_reference< const T > engine::SharedTaskWithResult< T >::Get ( ) &&

inline

Definition at line 87 of file shared_task_with_result.hpp.

Get() [2/2]

template<typename T >

decltype(auto) engine::SharedTaskWithResult< T >::Get ( ) const &

inline

Returns (or rethrows) the result of task invocation. Task remains valid after return from this method, thread(coro)-safe.

Returns

const T& or void

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 76 of file shared_task_with_result.hpp.

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

• userver/engine/task/shared_task_with_result.hpp