Cooperative Exceptions for Concurrent Objects

The advent of multi-core systems set off a race to get concurrent programming to the masses. One of the challenging aspects of this type of system is how to deal with exceptional situations, since it is very difficult to assert the precise state of a concurrent program when an exception arises. In this paper we propose an exception-handling model for concurrent systems. Its main quality attributes are simplicity and expressiveness, allowing programmers to deal with exceptional situations in a concurrent setting in a familiar way. The proposal is centered on a new kind of exception type that defines new paths for exception propagation among concurrent threads of execution. In our model, beyond being able to control where exceptions are raised, the developer can define in which thread, and when during its execution, a particular exception will be handled. The proposed model has been implemented in Scala, and we show its application to the construction of concurrent software.