Fiber::SchedulerInterface

This is not an existing class, but documentation of the interface that Scheduler object should comply in order to be used as Fiber.scheduler and handle non-blocking fibers. See also the “Non-blocking fibers” section in Fiber class docs for explanations of some concepts.

Scheduler’s behavior and usage are expected to be as follows:

• When the execution in the non-blocking Fiber reaches some blocking operation (like sleep, wait for a process, or a non-ready I/O), it calls some of the scheduler’s hook methods, listed below.

• Scheduler somehow registers what the current fiber is waited for, and yields control to other fibers with Fiber.yield (so the fiber would be suspended while expecting its wait to end, and other fibers in the same thread can perform)

• At the end of the current thread execution, the scheduler’s method close is called

• The scheduler runs into a wait loop, checking all the blocked fibers (which it has registered on hook calls) and resuming them when the awaited resource is ready (I/O ready, sleep time passed).

A typical implementation would probably rely for this closing loop on a gem like EventMachine or Async.

This way concurrent execution will be achieved in a way that is transparent for every individual Fiber’s code.

Hook methods are:

• io_wait

• process_wait

• kernel_sleep

• block and unblock

• (the list is expanded as Ruby developers make more methods having non-blocking calls)

When not specified otherwise, the hook implementations are mandatory: if they are not implemented, the methods trying to call hook will fail. To provide backward compatibility, in the future hooks will be optional (if they are not implemented, due to the scheduler being created for the older Ruby version, the code which needs this hook will not fail, and will just behave in a blocking fashion).

It is also strongly suggested that the scheduler implement the fiber method, which is delegated to by Fiber.schedule.

Sample toy implementation of the scheduler can be found in Ruby’s code, in test/fiber/scheduler.rb