IronPython uses a combination of lock-free techniques and fine-grained locking. Reference counting is of course replaced with the .NET runtime GC. Single-thread

IronPython uses a combination of lock-free techniques and fine-grained locking. Reference counting is of course replaced with the .NET runtime GC. Single-threaded and multi-threaded performance suffers since this approach means pessimistically synchronizing all accesses, including those that are single-threaded.