Endpoint-based parallel data processing in a parallel active messaging interface of a parallel computer

A method of endpoint-based parallel data processing in a parallel active messaging interface ('PAMI') of a parallel computer, the parallel computer comprising a plurality of compute nodes that execute a parallel application, the PAMI comprising data communications endpoints, each endpoint comprising a specification of data communications parameters for a thread of execution on a compute node, including specifications of a client, a context, and a task, the endpoints coupled for data communications through the PAMI, the method comprising:

• establishing by an application-level entity, for collective operations of the PAMI, a data communications geometry, the geometry specifying, for tasks representing processes of execution of the parallel application, a set of endpoints that are used in collective operations of the PAMI, including a plurality of endpoints for one of the tasks;
• receiving in one or more endpoints of the geometry an instruction for a collective operation, the instruction specifying communications of transfer data among the endpoints of the geometry;
• and
• executing the instruction for a collective operation through the endpoints in dependence upon the geometry, including dividing data communications operations among the plurality of endpoints for one of the tasks.