lib/concurrent-ruby-edge/concurrent/edge/channel.rb
require 'concurrent/synchronization/object'
require 'concurrent/edge/promises'
# @!macro warn.edge
module Concurrent
module Promises
# A first in first out channel that accepts messages with push family of methods and returns
# messages with pop family of methods.
# Pop and push operations can be represented as futures, see {#pop_op} and {#push_op}.
# The capacity of the channel can be limited to support back pressure, use capacity option in {#initialize}.
# {#pop} method blocks ans {#pop_op} returns pending future if there is no message in the channel.
# If the capacity is limited the {#push} method blocks and {#push_op} returns pending future.
#
# {include:file:docs-source/channel.out.md}
# @!macro warn.edge
class Channel < Concurrent::Synchronization::Object
# TODO (pitr-ch 06-Jan-2019): rename to Conduit?, to be able to place it into Concurrent namespace?
# TODO (pitr-ch 14-Jan-2019): better documentation, do few examples from go
# TODO (pitr-ch 12-Dec-2018): implement channel closing,
# - as a child class? To also have a channel which cannot be closed.
# TODO (pitr-ch 26-Dec-2016): replace with lock-free implementation, at least getting a message when available should be lock free same goes for push with space available
# @!macro channel.warn.blocks
# @note This function potentially blocks current thread until it can continue.
# Be careful it can deadlock.
#
# @!macro channel.param.timeout
# @param [Numeric] timeout the maximum time in second to wait.
safe_initialization!
# Default capacity of the Channel, makes it accept unlimited number of messages.
UNLIMITED_CAPACITY = ::Object.new
UNLIMITED_CAPACITY.singleton_class.class_eval do
include Comparable
def <=>(other)
1
end
def to_s
'unlimited'
end
end
NOTHING = Object.new
private_constant :NOTHING
# An object which matches anything (with #===)
ANY = Object.new.tap do |any|
def any.===(other)
true
end
def any.to_s
'ANY'
end
end
# Create channel.
# @param [Integer, UNLIMITED_CAPACITY] capacity the maximum number of messages which can be stored in the channel.
def initialize(capacity = UNLIMITED_CAPACITY)
super()
@Capacity = capacity
@Mutex = Mutex.new
# TODO (pitr-ch 28-Jan-2019): consider linked lists or other data structures for following attributes, things are being deleted from the middle
@Probes = []
@Messages = []
@PendingPush = []
end
# Push the message into the channel if there is space available.
# @param [Object] message
# @return [true, false]
def try_push(message)
@Mutex.synchronize { ns_try_push(message) }
end
# Returns future which will fulfill when the message is pushed to the channel.
# @!macro chanel.operation_wait
# If it is later waited on the operation with a timeout e.g.`channel.pop_op.wait(1)`
# it will not prevent the channel to fulfill the operation later after the timeout.
# The operation has to be either processed later
# ```ruby
# pop_op = channel.pop_op
# if pop_op.wait(1)
# process_message pop_op.value
# else
# pop_op.then { |message| log_unprocessed_message message }
# end
# ```
# or the operation can be prevented from completion after timing out by using
# `channel.pop_op.wait(1, [true, nil, nil])`.
# It will fulfill the operation on timeout preventing channel from doing the operation,
# e.g. popping a message.
#
# @param [Object] message
# @return [ResolvableFuture(self)]
def push_op(message)
@Mutex.synchronize do
if ns_try_push(message)
Promises.fulfilled_future self
else
pushed = Promises.resolvable_future
@PendingPush.push message, pushed
return pushed
end
end
end
# Blocks current thread until the message is pushed into the channel.
#
# @!macro channel.warn.blocks
# @param [Object] message
# @!macro channel.param.timeout
# @return [self, true, false] self implies timeout was not used, true implies timeout was used
# and it was pushed, false implies it was not pushed within timeout.
def push(message, timeout = nil)
pushed_op = @Mutex.synchronize do
return timeout ? true : self if ns_try_push(message)
pushed = Promises.resolvable_future
# TODO (pitr-ch 06-Jan-2019): clear timed out pushes in @PendingPush, null messages
@PendingPush.push message, pushed
pushed
end
result = pushed_op.wait!(timeout, [true, self, nil])
result == pushed_op ? self : result
end
# @!macro promises.channel.try_pop
# Pop a message from the channel if there is one available.
# @param [Object] no_value returned when there is no message available
# @return [Object, no_value] message or nil when there is no message
def try_pop(no_value = nil)
try_pop_matching ANY, no_value
end
# @!macro promises.channel.try_pop
# @!macro promises.channel.param.matcher
# @param [#===] matcher only consider message which matches `matcher === a_message`
def try_pop_matching(matcher, no_value = nil)
@Mutex.synchronize do
message = ns_shift_message matcher
return message if message != NOTHING
message = ns_consume_pending_push matcher
return message != NOTHING ? message : no_value
end
end
# @!macro promises.channel.pop_op
# Returns a future witch will become fulfilled with a value from the channel when one is available.
# @!macro chanel.operation_wait
#
# @param [ResolvableFuture] probe the future which will be fulfilled with a channel value
# @return [Future(Object)] the probe, its value will be the message when available.
def pop_op(probe = Promises.resolvable_future)
@Mutex.synchronize { ns_pop_op(ANY, probe, false) }
end
# @!macro promises.channel.pop_op
# @!macro promises.channel.param.matcher
def pop_op_matching(matcher, probe = Promises.resolvable_future)
@Mutex.synchronize { ns_pop_op(matcher, probe, false) }
end
# @!macro promises.channel.pop
# Blocks current thread until a message is available in the channel for popping.
#
# @!macro channel.warn.blocks
# @!macro channel.param.timeout
# @param [Object] timeout_value a value returned by the method when it times out
# @return [Object, nil] message or nil when timed out
def pop(timeout = nil, timeout_value = nil)
pop_matching ANY, timeout, timeout_value
end
# @!macro promises.channel.pop
# @!macro promises.channel.param.matcher
def pop_matching(matcher, timeout = nil, timeout_value = nil)
# TODO (pitr-ch 27-Jan-2019): should it try to match pending pushes if it fails to match in the buffer? Maybe only if the size is zero. It could be surprising if it's used as a throttle it might be expected that it will not pop if buffer is full of messages which di not match, it might it expected it will block until the message is added to the buffer
# that it returns even if the buffer is full. User might expect that it has to be in the buffer first.
probe = @Mutex.synchronize do
message = ns_shift_message matcher
if message == NOTHING
message = ns_consume_pending_push matcher
return message if message != NOTHING
else
new_message = ns_consume_pending_push ANY
@Messages.push new_message unless new_message == NOTHING
return message
end
probe = Promises.resolvable_future
@Probes.push probe, false, matcher
probe
end
probe.value!(timeout, timeout_value, [true, timeout_value, nil])
end
# @!macro promises.channel.peek
# Behaves as {#try_pop} but it does not remove the message from the channel
# @param [Object] no_value returned when there is no message available
# @return [Object, no_value] message or nil when there is no message
def peek(no_value = nil)
peek_matching ANY, no_value
end
# @!macro promises.channel.peek
# @!macro promises.channel.param.matcher
def peek_matching(matcher, no_value = nil)
@Mutex.synchronize do
message = ns_shift_message matcher, false
return message if message != NOTHING
message = ns_consume_pending_push matcher, false
return message != NOTHING ? message : no_value
end
end
# @!macro promises.channel.try_select
# If message is available in the receiver or any of the provided channels
# the channel message pair is returned. If there is no message nil is returned.
# The returned channel is the origin of the message.
#
# @param [Channel, ::Array<Channel>] channels
# @return [::Array(Channel, Object), nil]
# pair [channel, message] if one of the channels is available for reading
def try_select(channels)
try_select_matching ANY, channels
end
# @!macro promises.channel.try_select
# @!macro promises.channel.param.matcher
def try_select_matching(matcher, channels)
message = nil
channel = [self, *channels].find do |ch|
message = ch.try_pop_matching(matcher, NOTHING)
message != NOTHING
end
channel ? [channel, message] : nil
end
# @!macro promises.channel.select_op
# When message is available in the receiver or any of the provided channels
# the future is fulfilled with a channel message pair.
# The returned channel is the origin of the message.
# @!macro chanel.operation_wait
#
# @param [Channel, ::Array<Channel>] channels
# @param [ResolvableFuture] probe the future which will be fulfilled with the message
# @return [ResolvableFuture(::Array(Channel, Object))] a future which is fulfilled with
# pair [channel, message] when one of the channels is available for reading
def select_op(channels, probe = Promises.resolvable_future)
select_op_matching ANY, channels, probe
end
# @!macro promises.channel.select_op
# @!macro promises.channel.param.matcher
def select_op_matching(matcher, channels, probe = Promises.resolvable_future)
[self, *channels].each { |ch| ch.partial_select_op matcher, probe }
probe
end
# @!macro promises.channel.select
# As {#select_op} but does not return future,
# it block current thread instead until there is a message available
# in the receiver or in any of the channels.
#
# @!macro channel.warn.blocks
# @param [Channel, ::Array<Channel>] channels
# @!macro channel.param.timeout
# @return [::Array(Channel, Object), nil] message or nil when timed out
# @see #select_op
def select(channels, timeout = nil)
select_matching ANY, channels, timeout
end
# @!macro promises.channel.select
# @!macro promises.channel.param.matcher
def select_matching(matcher, channels, timeout = nil)
probe = select_op_matching(matcher, channels)
probe.value!(timeout, nil, [true, nil, nil])
end
# @return [Integer] The number of messages currently stored in the channel.
def size
@Mutex.synchronize { @Messages.size }
end
# @return [Integer] Maximum capacity of the Channel.
def capacity
@Capacity
end
# @return [String] Short string representation.
def to_s
format '%s capacity taken %s of %s>', super[0..-2], size, @Capacity
end
alias_method :inspect, :to_s
class << self
# @see #try_select
# @return [::Array(Channel, Object)]
def try_select(channels)
channels.first.try_select(channels[1..-1])
end
# @see #select_op
# @return [Future(::Array(Channel, Object))]
def select_op(channels, probe = Promises.resolvable_future)
channels.first.select_op(channels[1..-1], probe)
end
# @see #select
# @return [::Array(Channel, Object), nil]
def select(channels, timeout = nil)
channels.first.select(channels[1..-1], timeout)
end
# @see #try_select_matching
# @return [::Array(Channel, Object)]
def try_select_matching(matcher, channels)
channels.first.try_select_matching(matcher, channels[1..-1])
end
# @see #select_op_matching
# @return [Future(::Array(Channel, Object))]
def select_op_matching(matcher, channels, probe = Promises.resolvable_future)
channels.first.select_op_matching(matcher, channels[1..-1], probe)
end
# @see #select_matching
# @return [::Array(Channel, Object), nil]
def select_matching(matcher, channels, timeout = nil)
channels.first.select_matching(matcher, channels[1..-1], timeout)
end
end
# @!visibility private
def partial_select_op(matcher, probe)
@Mutex.synchronize { ns_pop_op(matcher, probe, true) }
end
private
def ns_pop_op(matcher, probe, include_channel)
message = ns_shift_message matcher
# got message from buffer
if message != NOTHING
if probe.fulfill(include_channel ? [self, message] : message, false)
new_message = ns_consume_pending_push ANY
@Messages.push new_message unless new_message == NOTHING
else
@Messages.unshift message
end
return probe
end
# no message in buffer, try to pair with a pending push
i = 0
while true
message, pushed = @PendingPush[i, 2]
break if pushed.nil?
if matcher === message
value = include_channel ? [self, message] : message
if Promises::Resolvable.atomic_resolution(probe => [true, value, nil],
pushed => [true, self, nil])
@PendingPush[i, 2] = []
return probe
end
if probe.resolved?
return probe
end
# so pushed.resolved? has to be true, remove the push
@PendingPush[i, 2] = []
end
i += 2
end
# no push to pair with
# TODO (pitr-ch 11-Jan-2019): clear up probes when timed out, use callback
@Probes.push probe, include_channel, matcher if probe.pending?
return probe
end
def ns_consume_pending_push(matcher, remove = true)
i = 0
while true
message, pushed = @PendingPush[i, 2]
return NOTHING unless pushed
if matcher === message
resolved = pushed.resolved?
@PendingPush[i, 2] = [] if remove || resolved
# can fail if timed-out, so try without error
if remove ? pushed.fulfill(self, false) : !resolved
# pushed fulfilled so actually push the message
return message
end
end
i += 2
end
end
def ns_try_push(message)
i = 0
while true
probe, include_channel, matcher = @Probes[i, 3]
break unless probe
if matcher === message && probe.fulfill(include_channel ? [self, message] : message, false)
@Probes[i, 3] = []
return true
end
i += 3
end
if @Capacity > @Messages.size
@Messages.push message
true
else
false
end
end
def ns_shift_message(matcher, remove = true)
i = 0
while true
message = @Messages.fetch(i, NOTHING)
return NOTHING if message == NOTHING
if matcher === message
@Messages.delete_at i if remove
return message
end
i += 1
end
end
end
end
end