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tag: v0.2.0
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module EventMachine
module Synchrony
class ConnectionPool
def initialize(opts, &block)
@reserved = {} # map of in-progress connections
@available = [] # pool of free connections
@pending = [] # pending reservations (FIFO)
opts[:size].times do
@available.push(block.call) if block_given?
end
end
# Choose first available connection and pass it to the supplied
# block. This will block indefinitely until there is an available
# connection to service the request.
def execute(async)
f = Fiber.current
begin
conn = acquire(f)
yield conn
ensure
release(f) if not async
end
end
private
# Acquire a lock on a connection and assign it to executing fiber
# - if connection is available, pass it back to the calling block
# - if pool is full, yield the current fiber until connection is available
def acquire(fiber)
if conn = @available.pop
@reserved[fiber.object_id] = conn
conn
else
Fiber.yield @pending.push fiber
acquire(fiber)
end
end
# Release connection assigned to the supplied fiber and
# resume any other pending connections (which will
# immediately try to run acquire on the pool)
def release(fiber)
@available.push(@reserved.delete(fiber.object_id))
if pending = @pending.pop
pending.resume
end
end
# Allow the pool to behave as the underlying connection
#
# If the requesting method begins with "a" prefix, then
# hijack the callbacks and errbacks to fire a connection
# pool release whenever the request is complete. Otherwise
# yield the connection within execute method and release
# once it is complete (assumption: fiber will yield until
# data is available, or request is complete)
#
def method_missing(method, *args)
async = (method[0,1] == "a")
execute(async) do |conn|
df = conn.send(method, *args)
if async
fiber = Fiber.current
df.callback { release(fiber) }
df.errback { release(fiber) }
end
df
end
end
end
end
end
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