Completion processing for data communications instructions

A method of completion processing for data communications instructions in a distributed computing environment, the distributed computing environment including a plurality of computers coupled for data communications through communications adapters and an active messaging interface (‘AMI’), the method comprising:

• injecting, by the AMI for each of a sequence of data communications instructions into a slot in an injection FIFO buffer of a data communication adapter, a transfer descriptor specifying to the communications adapter a transfer of payload data according to each data communications instruction, at least some of the instructions specifying callback functions;
• injecting by the AMI a completion descriptor for each instruction that specifies a callback function into the next slot after that instruction's transfer descriptor in the injection FIFO buffer, the slot in which the completion descriptor is injected having a corresponding slot in a pending callback list;
• listing, by the AMI in the corresponding slot in the pending callback list for each data communications instruction that specifies a callback function, the callback function specified by that instruction;
• processing by the communications adapter each descriptor in the injection FIFO buffer, including transferring payload data as specified by each transfer descriptor and setting, as payload data for each completion descriptor, a bit that corresponds in a completion bit mask to the slot in the FIFO where the completion descriptor was injected, the completion bit mask comprising a plurality of bits, each bit corresponding to a slot in the injection FIFO buffer;
• and
• calling by the AMI any callback functions in the pending callback list for which transfers of payload data have been completed as indicated by set bits in the completion bit mask.