userver: engine::SharedTaskWithResult< T > Class Template Reference
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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.
 
SharedTaskWithResultoperator= (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.
 
SharedTaskWithResultoperator= (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.
 
SharedTaskoperator= (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.
 
SharedTaskoperator= (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
WaitInterruptedExceptionwhen current_task::IsCancelRequested() and no TaskCancellationBlockers are present.
TaskCancelledExceptionif no result is available because the task was cancelled

Definition at line 76 of file shared_task_with_result.hpp.


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