Awaiter Class Reference

#include <Pt/Coroutine.h>

Provides the base class for I/O-driven co_await-able operations. More...

Inherits AwaiterBase.

Inherited by BasicAwaiter< R >, BasicAwaiter< void >, AsyncAdvance, and AsyncYield.

Public Member Functions
bool	await_ready () const
	Returns false so co_await always suspends.
template<typename P >
bool	await_suspend (std::coroutine_handle< P > h)
	Starts the operation and suspends the coroutine.
void	cancel () override
	Cancels the in-flight operation.

Protected Member Functions
	Awaiter ()
	Constructor.
void	setReady ()
	Resumes the waiting coroutine. More...
virtual void	onBegin ()=0
	Starts the asynchronous operation. More...
virtual void	onCancel ()=0
	Aborts the in-flight operation. More...

Detailed Description

Derive from Awaiter to wrap an asynchronous operation so a Task or Generator can suspend until it completes. Implement Awaiter::onBegin() to subscribe to completion and start the work. Implement Awaiter::onCancel() to abort that work. Call Awaiter::setReady() when the operation finishes; that resumes the waiting coroutine.

Implement await_resume() in the subclass to deliver the result, or derive from BasicAwaiter when the awaitable only needs to produce a value through BasicAwaiter::onReady().

The following awaiter starts a device operation and resumes when the device signals completion:

class AsyncOp : public Pt::Awaiter
{
    public:
        explicit AsyncOp(Device& device)
        : _device(device)
        {}
 
        int await_resume()
        {
            return _device.endOp();
        }
 
    protected:
        void onBegin() override
        {
            _device.finished() += Pt::slot(*this, &AsyncOp::setReady);
            _device.beginOp();
        }
 
        void onCancel() override
        {
            _device.cancel();
        }
 
    private:
        Device& _device;
};

Member Function Documentation

setReady()

void setReady ( )

protected

Call this when the asynchronous operation has completed. Typically connect a completion signal to this method.

onBegin()

virtual void onBegin ( )

protectedpure virtual

Subscribe to completion and begin the work. The coroutine remains suspended until Awaiter::setReady() is called.

Implemented in AsyncYield.

onCancel()

virtual void onCancel ( )

protectedpure virtual

Called from Awaiter::cancel() when the waiting task or generator is cancelled.

Implemented in AsyncYield.