From 611c41f9393b625ed2badd316a882c3421e8a701 Mon Sep 17 00:00:00 2001
From: Patrick Mahoney <pat@polycrystal.org>
Date: Sat, 17 Dec 2011 21:51:22 -0600
Subject: [PATCH] Add SharedArray extension of SharedMemory (with Enumerable
 mixin).

---
 lib/process_shared/shared_array.rb       | 68 ++++++++++++++++++++++++
 spec/process_shared/shared_array_spec.rb | 26 +++++++++
 2 files changed, 94 insertions(+)
 create mode 100644 lib/process_shared/shared_array.rb
 create mode 100644 spec/process_shared/shared_array_spec.rb

diff --git a/lib/process_shared/shared_array.rb b/lib/process_shared/shared_array.rb
new file mode 100644
index 0000000..5454663
--- /dev/null
+++ b/lib/process_shared/shared_array.rb
@@ -0,0 +1,68 @@
+module ProcessShared
+  class SharedArray < SharedMemory
+    include Enumerable
+
+    # A fixed-size array in shared memory.  Processes forked from this
+    # one will be able to read and write shared data to the array.
+    # Access should be synchronized using a {Mutex}, {Semaphore}, or
+    # other means.
+    #
+    # Note that {Enumerable} methods such as {#map}, {#sort},
+    # etc. return new {Array} objects rather than modifying the shared
+    # array.
+    #
+    # @param [Symbol] type_or_count the data type as a symbol
+    # understood by FFI (e.g. :int, :double)
+    #
+    # @param [Integer] count number of array elements
+    def initialize(type_or_count = 1, count = 1)
+      super(type_or_count, count)
+
+      # See https://github.com/ffi/ffi/issues/118
+      ffi_type = FFI.find_type(self.type)
+
+      name, _ = FFI::TypeDefs.find do |(name, t)|
+        t == ffi_type
+      end
+
+      unless name
+        raise ArgumentError, "could not find FFI::Type for #{self.type}"
+      end
+      
+      getter = "get_#{name}"
+      setter = "put_#{name}"
+
+      # singleton class
+      sclass = class << self; self; end
+
+      unless sclass.method_defined?(getter)
+        raise ArgumentError, "no element getter for #{self.type} (#{getter})"
+      end
+
+      unless sclass.method_defined?(setter)
+        raise ArgumentError, "no element setter for #{self.type} (#{setter})"
+      end
+
+      sclass.send(:alias_method, :get_type, getter)
+      sclass.send(:alias_method, :put_type, setter)
+    end
+
+    def each
+      # NOTE: using @count because Enumerable defines its own count
+      # method...
+      @count.times { |i| yield self[i] }
+    end
+
+    def each_with_index
+      @count.times { |i| yield self[i], i }
+    end
+
+    def [](i)
+      get_type(i * self.type_size)
+    end
+
+    def []=(i, val)
+      put_type(i * self.type_size, val)
+    end
+  end
+end
diff --git a/spec/process_shared/shared_array_spec.rb b/spec/process_shared/shared_array_spec.rb
new file mode 100644
index 0000000..f31ec2a
--- /dev/null
+++ b/spec/process_shared/shared_array_spec.rb
@@ -0,0 +1,26 @@
+require 'spec_helper'
+require 'process_shared/shared_array'
+
+module ProcessShared
+  describe SharedArray do
+    it 'initializes arrays' do
+      mem = SharedArray.new(:int, 10)
+      10.times do |i|
+        mem[i] = i
+      end
+      10.times do |i|
+        mem[i].must_equal i
+      end
+    end
+
+    it 'responds to Enumerable methods' do
+      mem = SharedArray.new(:int, 4)
+      4.times do |i|
+        mem[i] = i+1
+      end
+
+      mem.map { |i| i * 2 }.must_equal [2, 4, 6, 8]
+      mem.sort.must_equal [1, 2, 3, 4]
+    end
+  end
+end