Add bin and edit workflow

bin/gems/concurrent-ruby-1.3.5/lib/concurrent-ruby/concurrent/mvar.rb

@@ -0,0 +1,242 @@
+require 'concurrent/concern/dereferenceable'
+require 'concurrent/synchronization/object'
+
+module Concurrent
+
+  # An `MVar` is a synchronized single element container. They are empty or
+  # contain one item. Taking a value from an empty `MVar` blocks, as does
+  # putting a value into a full one. You can either think of them as blocking
+  # queue of length one, or a special kind of mutable variable.
+  #
+  # On top of the fundamental `#put` and `#take` operations, we also provide a
+  # `#mutate` that is atomic with respect to operations on the same instance.
+  # These operations all support timeouts.
+  #
+  # We also support non-blocking operations `#try_put!` and `#try_take!`, a
+  # `#set!` that ignores existing values, a `#value` that returns the value
+  # without removing it or returns `MVar::EMPTY`, and a `#modify!` that yields
+  # `MVar::EMPTY` if the `MVar` is empty and can be used to set `MVar::EMPTY`.
+  # You shouldn't use these operations in the first instance.
+  #
+  # `MVar` is a [Dereferenceable](Dereferenceable).
+  #
+  # `MVar` is related to M-structures in Id, `MVar` in Haskell and `SyncVar` in Scala.
+  #
+  # Note that unlike the original Haskell paper, our `#take` is blocking. This is how
+  # Haskell and Scala do it today.
+  #
+  # @!macro copy_options
+  #
+  # ## See Also
+  #
+  # 1. P. Barth, R. Nikhil, and Arvind. [M-Structures: Extending a parallel, non- strict, functional language with state](http://dl.acm.org/citation.cfm?id=652538). In Proceedings of the 5th
+  #    ACM Conference on Functional Programming Languages and Computer Architecture (FPCA), 1991.
+  #
+  # 2. S. Peyton Jones, A. Gordon, and S. Finne. [Concurrent Haskell](http://dl.acm.org/citation.cfm?id=237794).
+  #    In Proceedings of the 23rd Symposium on Principles of Programming Languages
+  #    (PoPL), 1996.
+  class MVar < Synchronization::Object
+    include Concern::Dereferenceable
+    safe_initialization!
+
+    # Unique value that represents that an `MVar` was empty
+    EMPTY = ::Object.new
+
+    # Unique value that represents that an `MVar` timed out before it was able
+    # to produce a value.
+    TIMEOUT = ::Object.new
+
+    # Create a new `MVar`, either empty or with an initial value.
+    #
+    # @param [Hash] opts the options controlling how the future will be processed
+    #
+    # @!macro deref_options
+    def initialize(value = EMPTY, opts = {})
+      @value = value
+      @mutex = Mutex.new
+      @empty_condition = ConditionVariable.new
+      @full_condition = ConditionVariable.new
+      set_deref_options(opts)
+    end
+
+    # Remove the value from an `MVar`, leaving it empty, and blocking if there
+    # isn't a value. A timeout can be set to limit the time spent blocked, in
+    # which case it returns `TIMEOUT` if the time is exceeded.
+    # @return [Object] the value that was taken, or `TIMEOUT`
+    def take(timeout = nil)
+      @mutex.synchronize do
+        wait_for_full(timeout)
+
+        # If we timed out we'll still be empty
+        if unlocked_full?
+          value = @value
+          @value = EMPTY
+          @empty_condition.signal
+          apply_deref_options(value)
+        else
+          TIMEOUT
+        end
+      end
+    end
+
+    # acquires lock on the from an `MVAR`, yields the value to provided block,
+    # and release lock. A timeout can be set to limit the time spent blocked,
+    # in which case it returns `TIMEOUT` if the time is exceeded.
+    # @return [Object] the value returned by the block, or `TIMEOUT`
+    def borrow(timeout = nil)
+      @mutex.synchronize do
+        wait_for_full(timeout)
+
+        # if we timeoud out we'll still be empty
+        if unlocked_full?
+          yield @value
+        else
+          TIMEOUT
+        end
+      end
+    end
+
+    # Put a value into an `MVar`, blocking if there is already a value until
+    # it is empty. A timeout can be set to limit the time spent blocked, in
+    # which case it returns `TIMEOUT` if the time is exceeded.
+    # @return [Object] the value that was put, or `TIMEOUT`
+    def put(value, timeout = nil)
+      @mutex.synchronize do
+        wait_for_empty(timeout)
+
+        # If we timed out we won't be empty
+        if unlocked_empty?
+          @value = value
+          @full_condition.signal
+          apply_deref_options(value)
+        else
+          TIMEOUT
+        end
+      end
+    end
+
+    # Atomically `take`, yield the value to a block for transformation, and then
+    # `put` the transformed value. Returns the transformed value. A timeout can
+    # be set to limit the time spent blocked, in which case it returns `TIMEOUT`
+    # if the time is exceeded.
+    # @return [Object] the transformed value, or `TIMEOUT`
+    def modify(timeout = nil)
+      raise ArgumentError.new('no block given') unless block_given?
+
+      @mutex.synchronize do
+        wait_for_full(timeout)
+
+        # If we timed out we'll still be empty
+        if unlocked_full?
+          value = @value
+          @value = yield value
+          @full_condition.signal
+          apply_deref_options(value)
+        else
+          TIMEOUT
+        end
+      end
+    end
+
+    # Non-blocking version of `take`, that returns `EMPTY` instead of blocking.
+    def try_take!
+      @mutex.synchronize do
+        if unlocked_full?
+          value = @value
+          @value = EMPTY
+          @empty_condition.signal
+          apply_deref_options(value)
+        else
+          EMPTY
+        end
+      end
+    end
+
+    # Non-blocking version of `put`, that returns whether or not it was successful.
+    def try_put!(value)
+      @mutex.synchronize do
+        if unlocked_empty?
+          @value = value
+          @full_condition.signal
+          true
+        else
+          false
+        end
+      end
+    end
+
+    # Non-blocking version of `put` that will overwrite an existing value.
+    def set!(value)
+      @mutex.synchronize do
+        old_value = @value
+        @value = value
+        @full_condition.signal
+        apply_deref_options(old_value)
+      end
+    end
+
+    # Non-blocking version of `modify` that will yield with `EMPTY` if there is no value yet.
+    def modify!
+      raise ArgumentError.new('no block given') unless block_given?
+
+      @mutex.synchronize do
+        value = @value
+        @value = yield value
+        if unlocked_empty?
+          @empty_condition.signal
+        else
+          @full_condition.signal
+        end
+        apply_deref_options(value)
+      end
+    end
+
+    # Returns if the `MVar` is currently empty.
+    def empty?
+      @mutex.synchronize { @value == EMPTY }
+    end
+
+    # Returns if the `MVar` currently contains a value.
+    def full?
+      !empty?
+    end
+
+    protected
+
+    def synchronize(&block)
+      @mutex.synchronize(&block)
+    end
+
+    private
+
+    def unlocked_empty?
+      @value == EMPTY
+    end
+
+    def unlocked_full?
+      ! unlocked_empty?
+    end
+
+    def wait_for_full(timeout)
+      wait_while(@full_condition, timeout) { unlocked_empty? }
+    end
+
+    def wait_for_empty(timeout)
+      wait_while(@empty_condition, timeout) { unlocked_full? }
+    end
+
+    def wait_while(condition, timeout)
+      if timeout.nil?
+        while yield
+          condition.wait(@mutex)
+        end
+      else
+        stop = Concurrent.monotonic_time + timeout
+        while yield && timeout > 0.0
+          condition.wait(@mutex, timeout)
+          timeout = stop - Concurrent.monotonic_time
+        end
+      end
+    end
+  end
+end