The default model for each network operation is to first post it and then test for completion. However, there are often instances in which operations can complete immediately (during the post procedure) and thus do not require the extra test step. Examples of this occur when TCP sockets buffers are large enough to allow a message to be sent in one step without blocking. This may also occur on the receive side of communications if the required data has already been buffered by the BMI library when the receive operation is posted.
In these situations, it would be good to avoid the overhead of needlessly calling the test function. We therefore allow immediate completion from any post function. Immediate completion is indicated from post functions by a return value of one. BMI library users should always check this return value so that they are aware of opportunities to skip the test phase of communication.