BarrierTaskContext.
allGather
This function blocks until all tasks in the same stage have reached this routine. Each task passes in a message and returns with a list of all the messages passed in by each of those tasks.
New in version 3.0.0.
Warning
In a barrier stage, each task much have the same number of allGather() calls, in all possible code branches. Otherwise, you may get the job hanging or a SparkException after timeout.
Notes
This API is experimental