shared_future Class
The latest version of this topic can be found at 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
Do not call any methods other than valid, operator=, and the destructor on a shared_future object that's empty.
shared_future objects are not 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::shared_future Constructor | Constructs a shared_future object. |
Public Methods
| Name | Description |
|---|---|
| shared_future::get Method | Retrieves the result that's stored in the associated asynchronous state. |
| shared_future::valid Method | Specifies whether the object is not empty. |
| shared_future::wait Method | Blocks the current thread until the associated asynchronous state is ready. |
| shared_future::wait_for Method | Blocks until the associated asynchronous state is ready or until the specified time has elapsed. |
| shared_future::wait_until Method | 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 Method
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 Method
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 Method
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 Method
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 Method
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.