FIbers promise.

[Christian Rivasseau]

Hi everybody,

Thanks for the folly library.

I am a little confused with "folly/futures/Promise.h" and "folly/fibers/Promise.h";
What's the point of having 2 classes given that the fibers docs specifically state that

The good news are, folly::Future is already fibers-compatible.

When would one prefer fibers::Promise over folly::Promise?
Are there any plans to unite the 2?

Thanks a lot,

[sanj...@gmail.com]

You need both.  With fibers, you need fiber-compliant mutexes, futures etc
because scheduling of tasks inside a fiber is co-operative.  Every exposed api
must yield to the FiberManager instead of yielding to the underlying thread scheduler

[Christian]

Sanjos, it seems the doc indicates that regular futures are compliant with fibers?

The good news are, folly::Future is already fibers-compatible....

Calling get() on a folly::Future object will only suspend the calling fiber-task. It won't block the system thread, letting it process other tasks.

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[sanj...@gmail.com]

In the future, please provide a link to the document cited :-)
https://github.com/facebook/folly/blob/master/folly/fibers/README.md

I would have to dig deeper into the implementation to understand how the Future detects whether it being executed in a fiber.  I dont have the time for that right now, but generally speaking, as the doc says they do some magic under-cover using Batons.   Maybe someone else has a more accurate answer.

-Sandeep

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