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selector.rb
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selector.rb
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# frozen_string_literal: true
require "set"
module NIO
# Selectors monitor IO objects for events of interest
class Selector
# Return supported backends as symbols
#
# See `#backend` method definition for all possible backends
def self.backends
[:ruby]
end
# Create a new NIO::Selector
def initialize(backend = :ruby)
raise ArgumentError, "unsupported backend: #{backend}" unless backend == :ruby
@selectables = {}
@lock = Mutex.new
# Other threads can wake up a selector
@wakeup, @waker = IO.pipe
@closed = false
end
# Return a symbol representing the backend I/O multiplexing mechanism used.
# Supported backends are:
# * :ruby - pure Ruby (i.e IO.select)
# * :java - Java NIO on JRuby
# * :epoll - libev w\ Linux epoll
# * :poll - libev w\ POSIX poll
# * :kqueue - libev w\ BSD kqueue
# * :select - libev w\ SysV select
# * :port - libev w\ I/O completion ports
# * :unknown - libev w\ unknown backend
def backend
:ruby
end
# Register interest in an IO object with the selector for the given types
# of events. Valid event types for interest are:
# * :r - is the IO readable?
# * :w - is the IO writeable?
# * :rw - is the IO either readable or writeable?
def register(io, interest)
io = IO.try_convert(io)
@lock.synchronize do
raise IOError, "selector is closed" if closed?
monitor = @selectables[io]
raise ArgumentError, "already registered as #{monitor.interests.inspect}" if monitor
monitor = Monitor.new(io, interest, self)
@selectables[monitor.io] = monitor
monitor
end
end
# Deregister the given IO object from the selector
def deregister(io)
@lock.synchronize do
monitor = @selectables.delete IO.try_convert(io)
monitor.close(false) if monitor && !monitor.closed?
monitor
end
end
# Is the given IO object registered with the selector?
def registered?(io)
@lock.synchronize { @selectables.key? io }
end
# Select which monitors are ready
def select(timeout = nil)
selected_monitors = Set.new
@lock.synchronize do
readers = [@wakeup]
writers = []
@selectables.each do |io, monitor|
readers << io if monitor.interests == :r || monitor.interests == :rw
writers << io if monitor.interests == :w || monitor.interests == :rw
monitor.readiness = nil
end
ready_readers, ready_writers = Kernel.select(readers, writers, [], timeout)
return unless ready_readers # timeout
ready_readers.each do |io|
if io == @wakeup
# Clear all wakeup signals we've received by reading them
# Wakeups should have level triggered behavior
@wakeup.read(@wakeup.stat.size)
else
monitor = @selectables[io]
monitor.readiness = :r
selected_monitors << monitor
end
end
ready_writers.each do |io|
monitor = @selectables[io]
monitor.readiness = monitor.readiness == :r ? :rw : :w
selected_monitors << monitor
end
end
if block_given?
selected_monitors.each { |m| yield m }
selected_monitors.size
else
selected_monitors.to_a
end
end
# Wake up a thread that's in the middle of selecting on this selector, if
# any such thread exists.
#
# Invoking this method more than once between two successive select calls
# has the same effect as invoking it just once. In other words, it provides
# level-triggered behavior.
def wakeup
# Send the selector a signal in the form of writing data to a pipe
begin
@waker.write_nonblock "\0"
rescue IO::WaitWritable
# This indicates the wakeup pipe is full, which means the other thread
# has already received many wakeup calls, but not processed them yet.
# The other thread will completely drain this pipe when it wakes up,
# so it's ok to ignore this exception if it occurs: we know the other
# thread has already been signaled to wake up
end
nil
end
# Close this selector and free its resources
def close
@lock.synchronize do
return if @closed
begin
@wakeup.close
rescue IOError
end
begin
@waker.close
rescue IOError
end
@closed = true
end
end
# Is this selector closed?
def closed?
@closed
end
def empty?
@selectables.empty?
end
end
end