Hello, as a result of recently happened discussion about atomic operations, i implemented two kinds of thread-safe queues FIFO and LIFO, which using atomic operations, instead of semaphore to add/remove items. You may review it by loading the code from SqueakSource: MCHttpRepository location: 'http://www.squeaksource.com/Atomics' user: '' password: '' FIFOQueue scales much better than SharedQueue, and after some additional testing can fully replace it. I tested FIFOQueue by replacing a SharedQueue class for EventSensor (a core system part, responsible for delivering events). In attached file you can find a patch, which will make your sensor to work with FIFOQueue, after you save image, or do 'EventSensor install'. There are also a heavy-concurrency tests in corresponding test classes, which is passing ok. Concurrency is highly complex field, thus i won't be surprised if code still contains a bugs. Code license is MIT, moreover a repository is publicly writeable, so if you wanna add tests, benchmarks, fixes, or implement new kind of lock-free container, feel free to do it. Any feedback is welcome. -- Best regards, Igor Stasenko AKA sig.