Concurrent Clustered Programming

We present the concurrency and distribution primitives of

X10

, a modern, statically typed, class-based object-oriented (OO) programming language, designed for high productivity programming of scalable applications on high-end machines. The basic move in the

X10

programming model is to reify locality through a notion of

place

, which hosts multiple data items and activities that operate on them. Aggregate objects (such as arrays) may be distributed across multiple places. Activities may dynamically spawn new activities in mulitple places and sequence them through a

finish

operation that detects termination of activities. Atomicity is obtained through the use of

atomic blocks

. Activities may repeatedly detect quiescence of a data-dependent collection of (distributed) activities through a notion of

clocks

, generalizing barriers. Thus

X10

has a handful of orthogonal constructs for

space

,

time

,

sequencing

and

atomicity

.

X10

smoothly combines and generalizes the current dominant paradigms for shared memory computing and message passing.

We present a bisimulation-based operational semantics for

X10

building on the formal semantics for “Middleweight Java”. We establish the central theorem of

X10

: programs without conditional atomic blocks do not deadlock.