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| | # -*- encoding: binary -*-
require 'thread'
module Rainbows
# Rack middleware to limit application-level concurrency independently
# of network conncurrency in \Rainbows! Since the +worker_connections+
# option in \Rainbows! is only intended to limit the number of
# simultaneous clients, this middleware may be used to limit the
# number of concurrent application dispatches independently of
# concurrent clients.
#
# Instead of using M:N concurrency in \Rainbows!, this middleware
# allows M:N:P concurrency where +P+ is the AppPool +:size+ while
# +M+ remains the number of +worker_processes+ and +N+ remains the
# number of +worker_connections+.
#
# rainbows master
# \_ rainbows worker[0]
# | \_ client[0,0]------\ ___app[0]
# | \_ client[0,1]-------\ /___app[1]
# | \_ client[0,2]-------->--< ...
# | ... __/ `---app[P]
# | \_ client[0,N]----/
# \_ rainbows worker[1]
# | \_ client[1,0]------\ ___app[0]
# | \_ client[1,1]-------\ /___app[1]
# | \_ client[1,2]-------->--< ...
# | ... __/ `---app[P]
# | \_ client[1,N]----/
# \_ rainbows worker[M]
# \_ client[M,0]------\ ___app[0]
# \_ client[M,1]-------\ /___app[1]
# \_ client[M,2]-------->--< ...
# ... __/ `---app[P]
# \_ client[M,N]----/
#
# AppPool should be used if you want to enforce a lower value of +P+
# than +N+.
#
# AppPool has no effect on the Rev concurrency model as that is
# single-threaded/single-instance as far as application concurrency goes.
# In other words, +P+ is always +one+ when using Rev. AppPool currently
# only works with the ThreadSpawn and ThreadPool models. It does not
# yet work reliably with the Revactor model, yet.
#
# Since this is Rack middleware, you may load this in your Rack
# config.ru file and even use it in servers other than \Rainbows!
#
# use Rainbows::AppPool, :size => 30
# map "/lobster" do
# run Rack::Lobster.new
# end
#
# You may to load this earlier or later in your middleware chain
# depending on the concurrency/copy-friendliness of your middleware(s).
class AppPool < Struct.new(:pool)
# +opt+ is a hash, +:size+ is the size of the pool (default: 6)
# meaning you can have up to 6 concurrent instances of +app+
# within one \Rainbows! worker process. We support various
# methods of the +:copy+ option: +dup+, +clone+, +deep+ and +none+.
# Depending on your +app+, one of these options should be set.
# The default +:copy+ is +:dup+ as is commonly seen in existing
# Rack middleware.
def initialize(app, opt = {})
self.pool = Queue.new
(1...(opt[:size] || 6)).each do
pool << case (opt[:copy] || :dup)
when :none then app
when :dup then app.dup
when :clone then app.clone
when :deep then Marshal.load(Marshal.dump(app)) # unlikely...
else
raise ArgumentError, "unsupported copy method: #{opt[:copy].inspect}"
end
end
pool << app # the original
end
# Rack application endpoint, +env+ is the Rack environment
def call(env)
app = pool.shift
app.call(env)
ensure
pool << app
end
end
end
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