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:
-
(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
static VALUE
rb_fiber_scheduler_interface_block(VALUE self)
{
}
Invoked by methods like Thread.join
, and by Mutex
, to signify that current Fiber
is blocked till further notice (e.g. unblock
) or till timeout
will pass.
blocker
is what we are waiting on, informational only (for debugging and logging). There are no guarantees about its value.
Expected to return boolean, specifying whether the blocking operation was successful or not.
static VALUE
rb_fiber_scheduler_interface_close(VALUE self)
{
}
Called when the current thread exits. The scheduler is expected to implement this method in order to allow all waiting fibers to finalize their execution.
The suggested pattern is to implement the main event loop in the close
method.
static VALUE
rb_fiber_scheduler_interface_fiber(VALUE self)
{
}
Implementation of the Fiber.schedule
. The method is expected to immediately run passed block of code in a separate non-blocking fiber, and to return that Fiber
.
Minimal suggested implementation is:
def fiber(&block) Fiber.new(blocking: false, &block).tap(&:resume) end
static VALUE
rb_fiber_scheduler_interface_io_wait(VALUE self)
{
}
Invoked by IO#wait
, IO#wait_readable
, IO#wait_writable
to ask whether the specified descriptor is ready for specified events within the specified timeout
.
events
is a bit mask of IO::READABLE
, IO::WRITABLE
, and IO::PRIORITY
.
Suggested implementation should register which Fiber
is waiting for which resources and immediately calling Fiber.yield
to pass control to other fibers. Then, in the close
method, the scheduler might dispatch all the I/O resources to fibers waiting for it.
Expected to return the subset of events that are ready immediately.
static VALUE
rb_fiber_scheduler_interface_kernel_sleep(VALUE self)
{
}
Invoked by Kernel#sleep
and Mutex#sleep
and is expected to provide an implementation of sleeping in a non-blocking way. Implementation might register the current fiber in some list of “what fiber waits till what moment”, call Fiber.yield
to pass control, and then in close
resume the fibers whose wait period have ended.
static VALUE
rb_fiber_scheduler_interface_process_wait(VALUE self)
{
}
Invoked by Process::Status.wait
in order to wait for a specified process. See that method description for arguments description.
Suggested minimal implementation:
Thread.new do Process::Status.wait(pid, flags) end.value
This hook is optional: if it is not present in the current scheduler, Process::Status.wait
will behave as a blocking method.
Expected to returns a Process::Status
instance.
static VALUE
rb_fiber_scheduler_interface_unblock(VALUE self)
{
}
Invoked to wake up Fiber
previously blocked with block
(for example, Mutex#lock
calls block
and Mutex#unlock
calls unblock
). The scheduler should use the fiber
parameter to understand which fiber is unblocked.
blocker
is what was awaited for, but it is informational only (for debugging and logging), and it is not guaranteed to be the same value as the blocker
for block
.