shared_future Class

Describes an asynchronous return object. In contrast with a future object, an asynchronous provider can be associated with any number of shared_future objects.

Syntax

template <class Ty>
class shared_future;

Remarks

Don't call any methods other than valid, operator=, and the destructor on a shared_future object that's empty.

shared_future objects aren't synchronized. Calling methods on the same object from multiple threads introduces a data race that has unpredictable results.

Members

Public Constructors

Name	Description
shared_future	Constructs a shared_future object.

Public Methods

Name	Description
get	Retrieves the result that's stored in the associated asynchronous state.
valid	Specifies whether the object isn't empty.
wait	Blocks the current thread until the associated asynchronous state is ready.
wait_for	Blocks until the associated asynchronous state is ready or until the specified time has elapsed.
wait_until	Blocks until the associated asynchronous state is ready or until a specified point in time.

Public Operators

Name	Description
shared_future::operator=	Assigns a new associated asynchronous state.

Requirements

Header: <future>

Namespace: std

shared_future::get

Retrieves the result that's stored in the associated asynchronous state.

const Ty& get() const;

Ty& get() const;

void get() const;

Remarks

If the result is an exception, the method rethrows it. Otherwise, the result is returned.

Before it retrieves the result, this method blocks the current thread until the associated asynchronous state is ready.

For the partial specialization shared_future<Ty&>, the stored value is effectively a reference to the object that was passed to the asynchronous provider as the return value.

Because no stored value exists for the specialization shared_future<void>, the method returns void.

shared_future::operator=

Transfers an associated asynchronous state from a specified object.

shared_future& operator=(shared_future&& Right) noexcept;
shared_future& operator=(const shared_future& Right);

Parameters

Right
A shared_future object.

Return Value

*this

Remarks

For the first operator, Right no longer has an associated asynchronous state after the operation.

For the second method, Right maintains its associated asynchronous state.

shared_future::shared_future Constructor

Constructs a shared_future object.

shared_future() noexcept;
shared_future(future<Ty>&& Right) noexcept;
shared_future(shared_future&& Right) noexcept;
shared_future(const shared_future& Right);

Parameters

Right
A future or shared_future object.

Remarks

The first constructor constructs a shared_future object that has no associated asynchronous state.

The second and third constructors construct a shared_future object and transfer the associated asynchronous state from Right. Right no longer has an associated asynchronous state.

The fourth constructor constructs a shared_future object that has the same associated asynchronous state as Right.

shared_future::valid

Specifies whether the object has an associated asynchronous state.

bool valid() noexcept;

Return Value

true if the object has an associated asynchronous state; otherwise, false.

shared_future::wait

Blocks the current thread until the associated asynchronous state is ready.

void wait() const;

Remarks

An associated asynchronous state is ready only if its asynchronous provider has stored a return value or stored an exception.

shared_future::wait_for

Blocks the current thread until the associated asynchronous state is ready or until a specified time has elapsed.

template <class Rep, class Period>
future_status wait_for(
    const chrono::duration<Rep, Period>& Rel_time) const;

Parameters

Rel_time
A chrono::duration object that specifies a maximum time interval that the thread blocks.

Return Value

A future_status that indicates the reason for returning.

Remarks

An associated asynchronous state is ready only if its asynchronous provider has stored a return value or stored an exception.

shared_future::wait_until

Blocks the current thread until the associated asynchronous state is ready or until after a specified time point.

template <class Clock, class Duration>
future_status wait_until(
    const chrono::time_point<Clock, Duration>& Abs_time) const;

Parameters

Abs_time
A chrono::time_point object that specifies a time after which the thread can unblock.

Return Value

A future_status that indicates the reason for returning.

Remarks

An associated asynchronous state is ready only if its asynchronous provider has stored a return value or stored an exception.

See also

Header Files Reference
<future>