Initial pass at a generic connection pool

.gitignore

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+*.gem
+.bundle
+Gemfile.lock
+pkg/*

Gemfile

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+source "http://rubygems.org"
+
+# Specify your gem's dependencies in connection_pool.gemspec
+gemspec

Rakefile

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+require 'bundler'
+Bundler::GemHelper.install_tasks

connection_pool.gemspec

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+# -*- encoding: utf-8 -*-
+require "./lib/connection_pool/version"
+
+Gem::Specification.new do |s|
+  s.name        = "connection_pool"
+  s.version     = ConnectionPool::VERSION
+  s.platform    = Gem::Platform::RUBY
+  s.authors     = ["Mike Perham"]
+  s.email       = ["mperham@gmail.com"]
+  s.homepage    = ""
+  s.description = s.summary = %q{Generic connection pool for Ruby}
+
+  s.files         = `git ls-files`.split("\n")
+  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
+  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
+  s.require_paths = ["lib"]
+end

lib/connection_pool.rb

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+require 'connection_pool/timed_queue'
+
+# Generic connection pool class for e.g. sharing a limited number of network connections
+# among many threads.  Note: Connections are eager created.
+#
+# Example usage with block (faster):
+#
+#    @pool = ConnectionPool.new { Redis.new }
+#
+#    @pool.with do |redis|
+#      redis.lpop if redis.llen('my-list') > 0
+#    end
+#
+# Example usage replacing a global connection (slower):
+#
+#    REDIS = ConnectionPool.new { Redis.new }
+#
+#    def do_work
+#      REDIS.lpop if REDIS.llen('my-list') > 0
+#    end
+#
+# Accepts the following options:
+# - :size - number of connections to pool, defaults to 5
+# - :timeout - amount of time to wait for a connection if none currently available, defaults to 5 seconds
+#
+class ConnectionPool
+  DEFAULTS = { :size => 5, :timeout => 5 }
+
+  def initialize(options={})
+    raise ArgumentError, 'Connection pool requires a block' unless block_given?
+
+    @available = TimedQueue.new
+    @options = DEFAULTS.merge(options)
+    @options[:size].times do
+      @available << yield
+    end
+    @busy = []
+  end
+
+  def with(&block)
+    yield checkout
+  ensure
+    checkin
+  end
+
+  def method_missing(name, *args)
+    checkout.send(name, *args)
+  ensure
+    checkin
+  end
+
+  private
+
+  def checkout
+    Thread.current[:"current-#{self.object_id}"] ||= begin
+      conn = @available.timed_pop(@options[:timeout])
+      @busy << conn
+      conn
+    end
+  end
+
+  def checkin
+    conn = Thread.current[:"current-#{self.object_id}"]
+    Thread.current[:"current-#{self.object_id}"] = nil
+    @busy.delete(conn)
+    @available << conn
+    nil
+  end
+
+end

lib/connection_pool/timed_queue.rb

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+require 'thread'
+require 'timeout'
+
+class TimedQueue
+  def initialize
+    @que = []
+    @waiting = []
+    @mutex = Mutex.new
+    @resource = ConditionVariable.new
+  end
+
+  def push(obj)
+    @mutex.synchronize do
+      @que.push obj
+      @resource.signal
+    end
+  end
+  alias << push
+
+  def timed_pop(timeout=0.5)
+    while true
+      @mutex.synchronize do
+        @waiting.delete(Thread.current)
+        if @que.empty?
+          @waiting.push Thread.current
+          @resource.wait(@mutex, timeout)
+          raise TimeoutError if @que.empty?
+        else
+          retval = @que.shift
+          @resource.signal
+          return retval
+        end
+      end
+    end
+  end
+
+  def empty?
+    @que.empty?
+  end
+
+  def clear
+    @que.clear
+  end
+
+  def length
+    @que.length
+  end
+end

lib/connection_pool/version.rb

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+module ConnectionPool
+  VERSION = "0.0.1"
+end