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-# Scheduler
-
-The scheduler interface is used to intercept blocking operations. A typical
-implementation would be a wrapper for a gem like `EventMachine` or `Async`. This
-design provides separation of concerns between the event loop implementation
-and application code. It also allows for layered schedulers which can perform
-instrumentation.
-
-## Interface
-
-This is the interface you need to implement.
-
-~~~ ruby
-class Scheduler
- # Wait for the given file descriptor to match the specified events within
- # the specified timeout.
- # @parameter event [Integer] A bit mask of `IO::READABLE`,
- # `IO::WRITABLE` and `IO::PRIORITY`.
- # @parameter timeout [Numeric] The amount of time to wait for the event in seconds.
- # @returns [Integer] The subset of events that are ready.
- def io_wait(io, events, timeout)
- end
-
- # Sleep the current task for the specified duration, or forever if not
- # specified.
- # @param duration [Numeric] The amount of time to sleep in seconds.
- def kernel_sleep(duration = nil)
- end
-
- # Block the calling fiber.
- # @parameter blocker [Object] What we are waiting on, informational only.
- # @parameter timeout [Numeric | Nil] The amount of time to wait for in seconds.
- # @returns [Boolean] Whether the blocking operation was successful or not.
- def block(blocker, timeout = nil)
- end
-
- # Unblock the specified fiber.
- # @parameter blocker [Object] What we are waiting on, informational only.
- # @parameter fiber [Fiber] The fiber to unblock.
- # @reentrant Thread safe.
- def unblock(blocker, fiber)
- end
-
- # Intercept the creation of a non-blocking fiber.
- # @returns [Fiber]
- def fiber(&block)
- Fiber.new(blocking: false, &block)
- end
-
- # Invoked when the thread exits.
- def close
- self.run
- end
-
- def run
- # Implement event loop here.
- end
-end
-~~~
-
-Additional hooks may be introduced in the future, we will use feature detection
-in order to enable these hooks.
-
-## Non-blocking Execution
-
-The scheduler hooks will only be used in special non-blocking execution
-contexts. Non-blocking execution contexts introduce non-determinism because the
-execution of scheduler hooks may introduce context switching points into your
-program.
-
-### Fibers
-
-Fibers can be used to create non-blocking execution contexts.
-
-~~~ ruby
-Fiber.new do
- puts Fiber.current.blocking? # false
-
- # May invoke `Fiber.scheduler&.io_wait`.
- io.read(...)
-
- # May invoke `Fiber.scheduler&.io_wait`.
- io.write(...)
-
- # Will invoke `Fiber.scheduler&.kernel_sleep`.
- sleep(n)
-end.resume
-~~~
-
-We also introduce a new method which simplifies the creation of these
-non-blocking fibers:
-
-~~~ ruby
-Fiber.schedule do
- puts Fiber.current.blocking? # false
-end
-~~~
-
-The purpose of this method is to allow the scheduler to internally decide the
-policy for when to start the fiber, and whether to use symmetric or asymmetric
-fibers.
-
-### IO
-
-By default, I/O is non-blocking. Not all operating systems support non-blocking
-I/O. Windows is a notable example where socket I/O can be non-blocking but pipe
-I/O is blocking. Provided that there *is* a scheduler and the current thread *is
-non-blocking*, the operation will invoke the scheduler.
-
-### Mutex
-
-The `Mutex` class can be used in a non-blocking context and is fiber specific.
-
-### ConditionVariable
-
-The `ConditionVariable` class can be used in a non-blocking context and is
-fiber-specific.
-
-### Queue / SizedQueue
-
-The `Queue` and `SizedQueue` classses can be used in a non-blocking context and
-are fiber-specific.
-
-### Thread
-
-The `Thread#join` operation can be used in a non-blocking context and is
-fiber-specific.