class Scheduler
Handles scheduling of fibers. Implements the fiber scheduler interface.
Nested
Definitions
def self.supported?
- public
Whether the fiber scheduler is supported.
Signature
- public
Since
stable-v1
.
Implementation
def self.supported?
true
end
def initialize(parent = nil, selector: nil)
- public
Create a new scheduler.
Signature
- public
Since
stable-v1
.-
parameter
parent
Node | Nil
The parent node to use for task hierarchy.
-
parameter
selector
IO::Event::Selector
The selector to use for event handling.
Implementation
def initialize(parent = nil, selector: nil)
super(parent)
@selector = selector || ::IO::Event::Selector.new(Fiber.current)
@interrupted = false
@blocked = 0
@busy_time = 0.0
@idle_time = 0.0
@timers = ::IO::Event::Timers.new
end
def load
Compute the scheduler load according to the busy and idle times that are updated by the run loop.
Signature
-
returns
Float
The load of the scheduler. 0.0 means no load, 1.0 means fully loaded or over-loaded.
Implementation
def load
total_time = @busy_time + @idle_time
# If the total time is zero, then the load is zero:
return 0.0 if total_time.zero?
# We normalize to a 1 second window:
if total_time > 1.0
ratio = 1.0 / total_time
@busy_time *= ratio
@idle_time *= ratio
# We don't need to divide here as we've already normalised it to a 1s window:
return @busy_time
else
return @busy_time / total_time
end
end
def scheduler_close(error = $!)
Invoked when the fiber scheduler is being closed.
Executes the run loop until all tasks are finished, then closes the scheduler.
Implementation
def scheduler_close(error = $!)
# If the execution context (thread) was handling an exception, we want to exit as quickly as possible:
unless error
self.run
end
ensure
self.close
end
def terminate
Terminate all child tasks.
Implementation
def terminate
# If that doesn't work, take more serious action:
@children&.each do |child|
child.terminate
end
return @children.nil?
end
def close
- public
Terminate all child tasks and close the scheduler.
Signature
- public
Since
stable-v1
.
Implementation
def close
self.run_loop do
until self.terminate
self.run_once!
end
end
Kernel.raise "Closing scheduler with blocked operations!" if @blocked > 0
ensure
# We want `@selector = nil` to be a visible side effect from this point forward, specifically in `#interrupt` and `#unblock`. If the selector is closed, then we don't want to push any fibers to it.
selector = @selector
@selector = nil
selector&.close
consume
end
def closed?
- public
Signature
-
returns
Boolean
Whether the scheduler has been closed.
- public
Since
stable-v1
.
Implementation
def closed?
@selector.nil?
end
def to_s
Signature
-
returns
String
A description of the scheduler.
Implementation
def to_s
"\#<#{self.description} #{@children&.size || 0} children (#{stopped? ? 'stopped' : 'running'})>"
end
def interrupt
- asynchronous
Interrupt the event loop and cause it to exit.
Signature
- asynchronous
May be called from any thread.
Implementation
def interrupt
@interrupted = true
@selector&.wakeup
end
def transfer
Transfer from the calling fiber to the event loop.
Implementation
def transfer
@selector.transfer
end
def yield
Yield the current fiber and resume it on the next iteration of the event loop.
Implementation
def yield
@selector.yield
end
def push(fiber)
Schedule a fiber (or equivalent object) to be resumed on the next loop through the reactor.
Signature
-
parameter
fiber
Fiber | Object
The object to be resumed on the next iteration of the run-loop.
Implementation
def push(fiber)
@selector.push(fiber)
end
def raise(...)
Raise an exception on a specified fiber with the given arguments.
This internally schedules the current fiber to be ready, before raising the exception, so that it will later resume execution.
Signature
-
parameter
fiber
Fiber
The fiber to raise the exception on.
-
parameter
*arguments
Array
The arguments to pass to the fiber.
Implementation
def raise(...)
@selector.raise(...)
end
def resume(fiber, *arguments)
Resume execution of the specified fiber.
Signature
-
parameter
fiber
Fiber
The fiber to resume.
-
parameter
arguments
Array
The arguments to pass to the fiber.
Implementation
def resume(fiber, *arguments)
@selector.resume(fiber, *arguments)
end
def block(blocker, timeout)
- asynchronous
Invoked when a fiber tries to perform a blocking operation which cannot continue. A corresponding call Async::Scheduler#unblock
must be performed to allow this fiber to continue.
Signature
- asynchronous
May only be called on same thread as fiber scheduler.
Implementation
def block(blocker, timeout)
# $stderr.puts "block(#{blocker}, #{Fiber.current}, #{timeout})"
fiber = Fiber.current
if timeout
timer = @timers.after(timeout) do
if fiber.alive?
fiber.transfer(false)
end
end
end
begin
@blocked += 1
@selector.transfer
ensure
@blocked -= 1
end
ensure
timer&.cancel!
end
def unblock(blocker, fiber)
- asynchronous
Signature
- asynchronous
May be called from any thread.
Implementation
def unblock(blocker, fiber)
# $stderr.puts "unblock(#{blocker}, #{fiber})"
# This operation is protected by the GVL:
if selector = @selector
selector.push(fiber)
selector.wakeup
end
end
def kernel_sleep(duration = nil)
- asynchronous
Signature
- asynchronous
May be non-blocking..
Implementation
def kernel_sleep(duration = nil)
if duration
self.block(nil, duration)
else
self.transfer
end
end
def address_resolve(hostname)
- asynchronous
Signature
- asynchronous
May be non-blocking..
Implementation
def address_resolve(hostname)
# On some platforms, hostnames may contain a device-specific suffix (e.g. %en0). We need to strip this before resolving.
# See <https://github.com/socketry/async/issues/180> for more details.
hostname = hostname.split("%", 2).first
::Resolv.getaddresses(hostname)
end
def io_wait(io, events, timeout = nil)
- asynchronous
Signature
- asynchronous
May be non-blocking..
Implementation
def io_wait(io, events, timeout = nil)
fiber = Fiber.current
if timeout
# If an explicit timeout is specified, we expect that the user will handle it themselves:
timer = @timers.after(timeout) do
fiber.transfer
end
elsif timeout = get_timeout(io)
# Otherwise, if we default to the io's timeout, we raise an exception:
timer = @timers.after(timeout) do
fiber.raise(::IO::TimeoutError, "Timeout (#{timeout}s) while waiting for IO to become ready!")
end
end
return @selector.io_wait(fiber, io, events)
ensure
timer&.cancel!
end
def process_wait(pid, flags)
- asynchronous
Wait for the specified process ID to exit.
Signature
-
parameter
pid
Integer
The process ID to wait for.
-
parameter
flags
Integer
A bit-mask of flags suitable for
Process::Status.wait
.-
returns
Process::Status
A process status instance.
- asynchronous
May be non-blocking..
Implementation
def process_wait(pid, flags)
return @selector.process_wait(Fiber.current, pid, flags)
end
def run_once(timeout = nil)
Run one iteration of the event loop. Does not handle interrupts.
Signature
-
parameter
timeout
Float | Nil
The maximum timeout, or if nil, indefinite.
-
returns
Boolean
Whether there is more work to do.
Implementation
def run_once(timeout = nil)
Kernel.raise "Running scheduler on non-blocking fiber!" unless Fiber.blocking?
if self.finished?
self.stop
end
# If we are finished, we stop the task tree and exit:
if @children.nil?
return false
end
return run_once!(timeout)
end
def stop
Stop all children, including transient children, ignoring any signals.
Implementation
def stop
@children&.each do |child|
child.stop
end
end
def run(...)
Run the reactor until all tasks are finished. Proxies arguments to #async
immediately before entering the loop, if a block is provided.
Implementation
def run(...)
Kernel.raise ClosedError if @selector.nil?
initial_task = self.async(...) if block_given?
self.run_loop do
run_once
end
return initial_task
end
def async(*arguments, **options, &block)
- deprecated
Start an asynchronous task within the specified reactor. The task will be executed until the first blocking call, at which point it will yield and and this method will return.
This is the main entry point for scheduling asynchronus tasks.
Signature
-
yields
{|task| ...}
Executed within the task.
-
returns
Task
The task that was scheduled into the reactor.
- deprecated
With no replacement.
Implementation
def async(*arguments, **options, &block)
Kernel.raise ClosedError if @selector.nil?
task = Task.new(Task.current? || self, **options, &block)
# I want to take a moment to explain the logic of this.
# When calling an async block, we deterministically execute it until the
# first blocking operation. We don't *have* to do this - we could schedule
# it for later execution, but it's useful to:
# - Fail at the point of the method call where possible.
# - Execute determinstically where possible.
# - Avoid scheduler overhead if no blocking operation is performed.
task.run(*arguments)
# Console.debug "Initial execution of task #{fiber} complete (#{result} -> #{fiber.alive?})..."
return task
end
def with_timeout(duration, exception = TimeoutError, message = "execution expired", &block)
Invoke the block, but after the specified timeout, raise class Async::TimeoutError
in any currenly blocking operation. If the block runs to completion before the timeout occurs or there are no non-blocking operations after the timeout expires, the code will complete without any exception.
Signature
-
parameter
duration
Numeric
The time in seconds, in which the task should complete.
Implementation
def with_timeout(duration, exception = TimeoutError, message = "execution expired", &block)
fiber = Fiber.current
timer = @timers.after(duration) do
if fiber.alive?
fiber.raise(exception, message)
end
end
yield timer
ensure
timer&.cancel!
end