Merge pull request #297 from ruby-concurrency/refactor/catomic-reference-get_and_set

CAtomicReference#get_and_set compares read value on update.

Author: jdantonio

Gemfile

@@ -7,19 +7,18 @@ group :development do
   gem 'rake', '~> 10.4.2'
   gem 'rake-compiler', '~> 0.9.5'
   gem 'gem-compiler', '~> 0.3.0'
-  gem 'benchmark-ips', '~> 2.1.1'
+  gem 'benchmark-ips', '~> 2.2.0'
+
+  # documentation
+  gem 'countloc', '~> 0.4.0', :platforms => :mri, :require => false
+  gem 'yard', '~> 0.8.7.6', :require => false
+  gem 'inch', '~> 0.6.2', :platforms => :mri, :require => false
+  gem 'redcarpet', '~> 3.2.3', platforms: :mri # understands github markdown
 end
 
 group :testing do
   gem 'rspec', '~> 3.2.0'
-  gem 'simplecov', '~> 0.9.2', :require => false
-  gem 'coveralls', '~> 0.7.11', :require => false
+  gem 'simplecov', '~> 0.10.0', :require => false
+  gem 'coveralls', '~> 0.8.1', :require => false
   gem 'timecop', '~> 0.7.3'
 end
-
-group :documentation do
-  gem 'countloc', '~> 0.4.0', :platforms => :mri, :require => false
-  gem 'yard', '~> 0.8.7.6', :require => false
-  gem 'inch', '~> 0.5.10', :platforms => :mri, :require => false
-  gem 'redcarpet', '~> 3.2.2', platforms: :mri # understands github markdown
-end

ext/concurrent/atomic_reference.c

@@ -50,9 +50,13 @@ VALUE ir_set(VALUE self, VALUE new_value) {
 }
 
 VALUE ir_get_and_set(VALUE self, VALUE new_value) {
-  VALUE old_value = ir_get(self);
-  ir_set(self, new_value);
-  return old_value;
+  VALUE old_value;
+  for (;;) {
+    old_value = ir_get(self);
+    if (ir_compare_and_set(self, old_value, new_value) == Qtrue) {
+      return old_value;
+    }
+  }
 }
 
 VALUE ir_compare_and_set(volatile VALUE self, VALUE expect_value, VALUE new_value) {