From fcbf63e62c627deae76c1b8cb8c0876c536ed811 Mon Sep 17 00:00:00 2001
From: Jari Vetoniemi <jari.vetoniemi@indooratlas.com>
Date: Mon, 16 Mar 2020 18:49:26 +0900
Subject: Fresh start

---
 jni/ruby/lib/weakref.rb | 106 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 jni/ruby/lib/weakref.rb

(limited to 'jni/ruby/lib/weakref.rb')

diff --git a/jni/ruby/lib/weakref.rb b/jni/ruby/lib/weakref.rb
new file mode 100644
index 0000000..cdcbabf
--- /dev/null
+++ b/jni/ruby/lib/weakref.rb
@@ -0,0 +1,106 @@
+require "delegate"
+
+# Weak Reference class that allows a referenced object to be
+# garbage-collected.
+#
+# A WeakRef may be used exactly like the object it references.
+#
+# Usage:
+#
+#   foo = Object.new            # create a new object instance
+#   p foo.to_s                  # original's class
+#   foo = WeakRef.new(foo)      # reassign foo with WeakRef instance
+#   p foo.to_s                  # should be same class
+#   GC.start                    # start the garbage collector
+#   p foo.to_s                  # should raise exception (recycled)
+#
+# == Example
+#
+# With help from WeakRef, we can implement our own rudimentary WeakHash class.
+#
+# We will call it WeakHash, since it's really just a Hash except all of it's
+# keys and values can be garbage collected.
+#
+#     require 'weakref'
+#
+#     class WeakHash < Hash
+#       def []= key, obj
+#         super WeakRef.new(key), WeakRef.new(obj)
+#       end
+#     end
+#
+# This is just a simple implementation, we've opened the Hash class and changed
+# Hash#store to create a new WeakRef object with +key+ and +obj+ parameters
+# before passing them as our key-value pair to the hash.
+#
+# With this you will have to limit your self to String keys, otherwise you
+# will get an ArgumentError because WeakRef cannot create a finalizer for a
+# Symbol. Symbols are immutable and cannot be garbage collected.
+#
+# Let's see it in action:
+#
+#   omg = "lol"
+#   c = WeakHash.new
+#   c['foo'] = "bar"
+#   c['baz'] = Object.new
+#   c['qux'] = omg
+#   puts c.inspect
+#   #=> {"foo"=>"bar", "baz"=>#<Object:0x007f4ddfc6cb48>, "qux"=>"lol"}
+#
+#   # Now run the garbage collector
+#   GC.start
+#   c['foo'] #=> nil
+#   c['baz'] #=> nil
+#   c['qux'] #=> nil
+#   omg      #=> "lol"
+#
+#   puts c.inspect
+#   #=> WeakRef::RefError: Invalid Reference - probably recycled
+#
+# You can see the local variable +omg+ stayed, although its reference in our
+# hash object was garbage collected, along with the rest of the keys and
+# values. Also, when we tried to inspect our hash, we got a WeakRef::RefError.
+# This is because these objects were also garbage collected.
+
+class WeakRef < Delegator
+
+  ##
+  # RefError is raised when a referenced object has been recycled by the
+  # garbage collector
+
+  class RefError < StandardError
+  end
+
+  @@__map = ::ObjectSpace::WeakMap.new
+
+  ##
+  # Creates a weak reference to +orig+
+  #
+  # Raises an ArgumentError if the given +orig+ is immutable, such as Symbol,
+  # Fixnum, or Float.
+
+  def initialize(orig)
+    case orig
+    when true, false, nil
+      @delegate_sd_obj = orig
+    else
+      @@__map[self] = orig
+    end
+    super
+  end
+
+  def __getobj__ # :nodoc:
+    @@__map[self] or defined?(@delegate_sd_obj) ? @delegate_sd_obj :
+      Kernel::raise(RefError, "Invalid Reference - probably recycled", Kernel::caller(2))
+  end
+
+  def __setobj__(obj) # :nodoc:
+  end
+
+  ##
+  # Returns true if the referenced object is still alive.
+
+  def weakref_alive?
+    @@__map.key?(self) or defined?(@delegate_sd_obj)
+  end
+end
-- 
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