Open nesting allows replacing the automatic detection of conflicting memory accesses used in transactional memory (TM) with programmer-specified higher-level conflict detection. Higher-level conflict detection allows removing conflicts of commuting operations where the automatic conflict detection is too conservative. Different conflict detection schemes are incompatible with each other and thus must operate on separate memory locations to prevent inconsistencies. Using open nesting, a programmer implements this separation manually using source code modifications possibly assisted by static checks.

Software transactional memory (STM) stores information regarding ownership of memory locations in ownership records. We present a scheme to realize a one-to-one mapping of ownership records to memory locations that has moderate memory overhead and is suitable for STM implementations on top of managed runtimes.

We explore a programming approach for concurrency that synchronizes all accesses to shared memory by default. Synchronization takes place by ensuring that all program code runs inside atomic sections even if the program code has external side effects. Threads are mapped to atomic sections that a programmer must explicitly split to increase concurrency.