I was told that Deferrals did not compose well with Rx. This motivated me to design the DeferOperation operator.
DeferOperation demonstrates how Rx can be extended by a few engineers to provide services for many. Another way to say this is that Rx allows Async Algorithms to be written once, carefully, so that many others can re-use them.
These are all references to the Windows 8.1 Accelerometer sample I am modifying.
DeferOperation defaults to the ui thread by reading the context off of the Window, but when the suspending event is fired the Window is not valid, so this uses the current thread scheduler explicitly. publish and connect_forever ensure that the work is done even if nothing subscribes the result.
The implementation follows.
The core of the DeferOperation operator is (cpprx/rx-winrt.hpp):
sop is the first lambda from the usage (cpprx/rx-winrt.hpp):
sob is the second lambda from the usage (the OperationPattern is passed so that the SuspendingOperation and the Deferral are available to the sequence if it wants to see the Deadline or Complete early, for example) (cpprx/rx-winrt.hpp)
Using will retrieve the resource (OperationPattern), subscribe to the result of sob and Dispose the resource when the subscription completes or errors.
OperationPattern provides the abstraction needed by Using. It will call get and complete the deferral (cpprx/rx-winrt.hpp):