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October 30, 2009 08:28
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simple eventmachine async iterator
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module EventMachine | |
# A simple iterator for concurrent asynchronous work. | |
# | |
# Unlike ruby's built-in iterators, the end of the current iteration cycle is signaled manually, | |
# instead of happening automatically after the yielded block finishes executing. For example: | |
# | |
# (0..10).each{ |num| } | |
# | |
# becomes: | |
# | |
# EM::Iterator.new(0..10).each{ |num,iter| iter.next } | |
# | |
# This is especially useful when doing asynchronous work via reactor libraries and | |
# functions. For example, given a sync and async http api: | |
# | |
# response = sync_http_get(url); ... | |
# async_http_get(url){ |response| ... } | |
# | |
# a synchronous iterator such as: | |
# | |
# responses = urls.map{ |url| sync_http_get(url) } | |
# ... | |
# puts 'all done!' | |
# | |
# could be written as: | |
# | |
# EM::Iterator.new(urls).map(proc{ |url,iter| | |
# async_http_get(url){ |res| | |
# iter.return(res) | |
# } | |
# }, proc{ |responses| | |
# ... | |
# puts 'all done!' | |
# }) | |
# | |
# Now, you can take advantage of the asynchronous api to issue requests in parallel. For example, | |
# to fetch 10 urls at a time, simply pass in a concurrency of 10: | |
# | |
# EM::Iterator.new(urls, 10).each do |url,iter| | |
# async_http_get(url){ iter.next } | |
# end | |
# | |
class Iterator | |
# Create a new parallel async iterator with specified concurrency. | |
# | |
# i = EM::Iterator.new(1..100, 10) | |
# | |
# will create an iterator over the range that processes 10 items at a time. Iteration | |
# is started via #each, #map or #inject | |
# | |
def initialize(list, concurrency = 1) | |
raise ArgumentError, 'argument must be enumerable' unless list.respond_to?(:to_enum) | |
@enum = list.to_enum | |
@concurrency = concurrency | |
@started = false | |
@ended = false | |
end | |
# Change the concurrency of this iterator. Workers will automatically be spawned or destroyed | |
# to accomodate the new concurrency level. | |
# | |
def concurrency=(val) | |
old = @concurrency | |
@concurrency = val | |
spawn_workers if val > old and @started and !@ended | |
end | |
attr_reader :concurrency | |
# Iterate over a set of items using the specified block or proc. | |
# | |
# EM::Iterator.new(1..100).each do |num, iter| | |
# puts num | |
# iter.next | |
# end | |
# | |
# An optional second proc is invoked after the iteration is complete. | |
# | |
# EM::Iterator.new(1..100).each( | |
# proc{ |num,iter| iter.next }, | |
# proc{ puts 'all done' } | |
# ) | |
# | |
def each(foreach=nil, after=nil, &blk) | |
raise ArgumentError, 'proc or block required for iteration' unless foreach ||= blk | |
raise RuntimeError, 'cannot iterate over an iterator more than once' if @started or @ended | |
@started = true | |
@pending = 0 | |
@workers = 0 | |
all_done = proc{ | |
after.call if after and @ended and @pending == 0 | |
} | |
@process_next = proc{ | |
unless @ended or @workers > @concurrency | |
begin | |
item = @enum.next | |
@pending += 1 | |
is_done = false | |
on_done = proc{ | |
raise RuntimeError, 'already completed this iteration' if is_done | |
is_done = true | |
@pending -= 1 | |
if @ended | |
all_done.call | |
else | |
EM.next_tick(@process_next) | |
end | |
} | |
class << on_done | |
alias :next :call | |
end | |
foreach.call(item, on_done) | |
rescue StopIteration | |
@ended = true | |
@workers -= 1 | |
all_done.call | |
end | |
else | |
@workers -= 1 | |
end | |
} | |
spawn_workers | |
self | |
end | |
# Collect the results of an asynchronous iteration into an array. | |
# | |
# EM::Iterator.new(%w[ pwd uptime uname date ], 2).map(proc{ |cmd,iter| | |
# EM.system(cmd){ |output,status| | |
# iter.return(output) | |
# } | |
# }, proc{ |results| | |
# p results | |
# }) | |
# | |
def map(foreach, after) | |
index = 0 | |
inject([], proc{ |results,item,iter| | |
i = index | |
index += 1 | |
is_done = false | |
on_done = proc{ |res| | |
raise RuntimeError, 'already returned a value for this iteration' if is_done | |
is_done = true | |
results[i] = res | |
iter.return(results) | |
} | |
class << on_done | |
alias :return :call | |
def next | |
raise NoMethodError, 'must call #return on a map iterator' | |
end | |
end | |
foreach.call(item, on_done) | |
}, proc{ |results| | |
after.call(results) | |
}) | |
end | |
# Inject the results of an asynchronous iteration onto a given object. | |
# | |
# EM::Iterator.new(%w[ pwd uptime uname date ], 2).inject({}, proc{ |hash,cmd,iter| | |
# EM.system(cmd){ |output,status| | |
# hash[cmd] = status.exitstatus == 0 ? output.strip : nil | |
# iter.return(hash) | |
# } | |
# }, proc{ |results| | |
# p results | |
# }) | |
# | |
def inject(obj, foreach, after) | |
each(proc{ |item,iter| | |
is_done = false | |
on_done = proc{ |res| | |
raise RuntimeError, 'already returned a value for this iteration' if is_done | |
is_done = true | |
obj = res | |
iter.next | |
} | |
class << on_done | |
alias :return :call | |
def next | |
raise NoMethodError, 'must call #return on an inject iterator' | |
end | |
end | |
foreach.call(obj, item, on_done) | |
}, proc{ | |
after.call(obj) | |
}) | |
end | |
private | |
# Spawn workers to consume items from the iterator's enumerator based on the current concurrency level. | |
# | |
def spawn_workers | |
EM.next_tick(start_worker = proc{ | |
if @workers < @concurrency | |
@workers += 1 | |
@process_next.call | |
EM.next_tick(start_worker) | |
end | |
}) | |
nil | |
end | |
end | |
end | |
if __FILE__ == $0 | |
$:.unshift File.join(File.dirname(__FILE__), '..') | |
require 'eventmachine' | |
# TODO: real tests | |
# TODO: pass in one object instead of two? .each{ |iter| puts iter.current; iter.next } | |
# TODO: support iter.pause/resume/stop/break/continue? | |
# TODO: create some exceptions instead of using RuntimeError | |
# TODO: support proc instead of enumerable? EM::Iterator.new(proc{ return queue.pop }) | |
EM.run{ | |
EM::Iterator.new(1..50).each{ |num,iter| p num; iter.next } | |
i = EM::Iterator.new(1..100, 5) | |
i.each(proc{|num,iter| | |
p num.to_s | |
iter.next | |
}, proc{ | |
p :done | |
}) | |
EM.add_timer(0.03){ | |
i.concurrency = 1 | |
} | |
EM.add_timer(0.04){ | |
i.concurrency = 3 | |
} | |
EM::Iterator.new(100..150).map(proc{ |num,iter| | |
EM.add_timer(0.01){ iter.return(num) } | |
}, proc{ |results| | |
p results | |
}) | |
EM::Iterator.new(%w[ pwd uptime uname date ], 2).inject({}, proc{ |hash,cmd,iter| | |
EM.system(cmd){ |output,status| | |
hash[cmd] = status.exitstatus == 0 ? output.strip : nil | |
iter.return(hash) | |
} | |
}, proc{ |results| | |
p results | |
}) | |
} | |
end |
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