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bin/gems/concurrent-ruby-1.3.5/lib/concurrent-ruby/concurrent/atomic/cyclic_barrier.rb

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+require 'concurrent/synchronization/lockable_object'
+require 'concurrent/utility/native_integer'
+
+module Concurrent
+
+  # A synchronization aid that allows a set of threads to all wait for each
+  # other to reach a common barrier point.
+  # @example
+  #   barrier = Concurrent::CyclicBarrier.new(3)
+  #   jobs    = Array.new(3) { |i| -> { sleep i; p done: i } }
+  #   process = -> (i) do
+  #     # waiting to start at the same time
+  #     barrier.wait
+  #     # execute job
+  #     jobs[i].call
+  #     # wait for others to finish
+  #     barrier.wait
+  #   end
+  #   threads = 2.times.map do |i|
+  #     Thread.new(i, &process)
+  #   end
+  #
+  #   # use main as well
+  #   process.call 2
+  #
+  #   # here we can be sure that all jobs are processed
+  class CyclicBarrier < Synchronization::LockableObject
+
+    # @!visibility private
+    Generation = Struct.new(:status)
+    private_constant :Generation
+
+    # Create a new `CyclicBarrier` that waits for `parties` threads
+    #
+    # @param [Fixnum] parties the number of parties
+    # @yield an optional block that will be executed that will be executed after
+    #  the last thread arrives and before the others are released
+    #
+    # @raise [ArgumentError] if `parties` is not an integer or is less than zero
+    def initialize(parties, &block)
+      Utility::NativeInteger.ensure_integer_and_bounds parties
+      Utility::NativeInteger.ensure_positive_and_no_zero parties
+
+      super(&nil)
+      synchronize { ns_initialize parties, &block }
+    end
+
+    # @return [Fixnum] the number of threads needed to pass the barrier
+    def parties
+      synchronize { @parties }
+    end
+
+    # @return [Fixnum] the number of threads currently waiting on the barrier
+    def number_waiting
+      synchronize { @number_waiting }
+    end
+
+    # Blocks on the barrier until the number of waiting threads is equal to
+    # `parties` or until `timeout` is reached or `reset` is called
+    # If a block has been passed to the constructor, it will be executed once by
+    #  the last arrived thread before releasing the others
+    # @param [Fixnum] timeout the number of seconds to wait for the counter or
+    #  `nil` to block indefinitely
+    # @return [Boolean] `true` if the `count` reaches zero else false on
+    #  `timeout` or on `reset` or if the barrier is broken
+    def wait(timeout = nil)
+      synchronize do
+
+        return false unless @generation.status == :waiting
+
+        @number_waiting += 1
+
+        if @number_waiting == @parties
+          @action.call if @action
+          ns_generation_done @generation, :fulfilled
+          true
+        else
+          generation = @generation
+          if ns_wait_until(timeout) { generation.status != :waiting }
+            generation.status == :fulfilled
+          else
+            ns_generation_done generation, :broken, false
+            false
+          end
+        end
+      end
+    end
+
+    # resets the barrier to its initial state
+    # If there is at least one waiting thread, it will be woken up, the `wait`
+    # method will return false and the barrier will be broken
+    # If the barrier is broken, this method restores it to the original state
+    #
+    # @return [nil]
+    def reset
+      synchronize { ns_generation_done @generation, :reset }
+    end
+
+    # A barrier can be broken when:
+    # - a thread called the `reset` method while at least one other thread was waiting
+    # - at least one thread timed out on `wait` method
+    #
+    # A broken barrier can be restored using `reset` it's safer to create a new one
+    # @return [Boolean] true if the barrier is broken otherwise false
+    def broken?
+      synchronize { @generation.status != :waiting }
+    end
+
+    protected
+
+    def ns_generation_done(generation, status, continue = true)
+      generation.status = status
+      ns_next_generation if continue
+      ns_broadcast
+    end
+
+    def ns_next_generation
+      @generation     = Generation.new(:waiting)
+      @number_waiting = 0
+    end
+
+    def ns_initialize(parties, &block)
+      @parties = parties
+      @action  = block
+      ns_next_generation
+    end
+  end
+end