# Concurrency question **URL:** \ **Category:** Ruby\ **Created:** [May 3, 2006, 10:00pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530 "2006-05-03T22:00:52Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 3, 2006, 10:00pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/1 "2006-05-03T22:00:52Z")
I am new to concurrency issues, and am working with DRb (also new to this). My DRb class assigns a value to an instance variable that will be accessed by my client. Is there a possibility with a concurrency issue if the client tries the access that variable when it is being assigned. i.e… @list = LabelList.new(@label\_list) Will I need a mutex around this? Thanks, Trish ---
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 3, 2006, 10:13pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/2 "2006-05-03T22:13:40Z")
On May 3, 2006, at 12:58 PM, Trish Ball wrote: > I am new to concurrency issues, and am working with DRb (also new to > this). My DRb class assigns a value to an instance variable that will > be accessed by my client. Is there a possibility with a concurrency > issue if the client tries the access that variable when it is being > assigned. No. > @list = LabelList.new(@label\_list) > > Will I need a mutex around this? It will see either the old value or the new value. Nothing will break otherwise. – Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net) This implementation is HODEL-HASH-9600 compliant [http://trackmap.robotcoop.com](http://trackmap.robotcoop.com) ---
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 4, 2006, 2:37pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/3 "2006-05-04T14:37:55Z")
2006/5/3, Eric H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > @list = LabelList.new(@label\_list) > > > > Will I need a mutex around this? > > It will see either the old value or the new value. Nothing will > break otherwise. IMHO this cannot be answered correctly with the information we have so far. You are right with regard to assignment semantics (i.e. assignment is atomic in current Ruby runtime) but inconsistencies might still occur if the object is to be changed or if there are other instance variables that have to be changed consistently. It really depends on the application context. Kind regards robert ---
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 4, 2006, 3:42pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/4 "2006-05-04T15:42:54Z")
On May 4, 2006, at 7:34 AM, Robert K. wrote: > > > assigned. > > > IMHO this cannot be answered correctly with the information we have so > > > far. The example had one client reading the value and one server setting it. Under those circumstances, I think Eric’s answer is right on. > You are right with regard to assignment semantics (i.e. > assignment is atomic in current Ruby runtime) I’m fairly certain assignment is not an atomic action in Ruby. There’s a pretty good example of this on page 142 of the PickAxe (2nd Edition). James Edward G. II ---
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 4, 2006, 7:36pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/5 "2006-05-04T19:36:48Z")
On Thu, May 04, 2006 at 10:40:19PM +0900, James Edward G. II wrote: > > You are right with regard to assignment semantics (i.e. > > assignment is atomic in current Ruby runtime) > > I’m fairly certain assignment is not an atomic action in Ruby. > There’s a pretty good example of this on page 142 of the PickAxe (2nd > Edition). Could you show that example? If it’s a variant of count = 0 (1…100).map do Thread.new { 10000.times { count += 1 } } end.each{|x| x.join} count # =\> 590000 it’s not saying quite the same thing (\>no atomic sugar heh). Besides, how would a regular assignment (foo = 1) be non-atomic?.. getting half a VALUE written, with the subsequent crash? 😉 ---
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 4, 2006, 9:56pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/6 "2006-05-04T21:56:47Z")
On May 4, 2006, at 12:55 PM, Eric H. wrote: > > > > that will > > > > > > > > > Will I need a mutex around this? > > > > > right on. > > > > > similar operations the code will need to be wrapped in a Mutex. > > > > > You’re right of course. My bad. James Edward G. II ---
**Author:** ![Trish\_Ball](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/edb3f5/32.png) [@Trish\_Ball](https://www.ruby-forum.com/u/Trish_Ball)\ **Post date:** [May 4, 2006, 7:58pm UTC](https://www.ruby-forum.com/t/concurrency-question/59530/7 "2006-05-04T19:58:20Z")
On May 4, 2006, at 6:40 AM, James Edward G. II wrote: > > > concurrency > > > It will see either the old value or the new value. Nothing will > > > assignment is atomic in current Ruby runtime) > > I’m fairly certain assignment is not an atomic action in Ruby. > There’s a pretty good example of this on page 142 of the PickAxe > (2nd Edition). Assignment is atomic. The example in the pickaxe shows that += is not atomic because it is two operations, not one. When performing similar operations the code will need to be wrapped in a Mutex. – Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net) This implementation is HODEL-HASH-9600 compliant [http://trackmap.robotcoop.com](http://trackmap.robotcoop.com)