srowen commented on a change in pull request #27640: [SPARK-30667][CORE] Add
all gather method to BarrierTaskContext
URL: https://github.com/apache/spark/pull/27640#discussion_r393029589
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File path: core/src/main/scala/org/apache/spark/BarrierTaskContext.scala
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@@ -163,6 +155,73 @@ class BarrierTaskContext private[spark] (
timerTask.cancel()
timer.purge()
}
+ json
+ }
+
+ /**
+ * :: Experimental ::
+ * Sets a global barrier and waits until all tasks in this stage hit this
barrier. Similar to
+ * MPI_Barrier function in MPI, the barrier() function call blocks until all
tasks in the same
+ * stage have reached this routine.
+ *
+ * CAUTION! In a barrier stage, each task must have the same number of
barrier() calls, in all
+ * possible code branches. Otherwise, you may get the job hanging or a
SparkException after
+ * timeout. Some examples of '''misuses''' are listed below:
+ * 1. Only call barrier() function on a subset of all the tasks in the same
barrier stage, it
+ * shall lead to timeout of the function call.
+ * {{{
+ * rdd.barrier().mapPartitions { iter =>
+ * val context = BarrierTaskContext.get()
+ * if (context.partitionId() == 0) {
+ * // Do nothing.
+ * } else {
+ * context.barrier()
+ * }
+ * iter
+ * }
+ * }}}
+ *
+ * 2. Include barrier() function in a try-catch code block, this may lead to
timeout of the
+ * second function call.
+ * {{{
+ * rdd.barrier().mapPartitions { iter =>
+ * val context = BarrierTaskContext.get()
+ * try {
+ * // Do something that might throw an Exception.
+ * doSomething()
+ * context.barrier()
+ * } catch {
+ * case e: Exception => logWarning("...", e)
+ * }
+ * context.barrier()
+ * iter
+ * }
+ * }}}
+ */
+ @Experimental
+ @Since("2.4.0")
+ def barrier(): Unit = {
+ runBarrier(RequestMethod.BARRIER)
+ ()
+ }
+
+ /**
+ * :: Experimental ::
+ * 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.
+ *
+ * CAUTION! The allGather method requires the same precautions as the
barrier method
+ *
+ * The message is type String rather than Array[Byte] because it is more
convenient for
+ * the user at the cost of worse performance.
+ */
+ @Experimental
+ @Since("3.0.0")
+ def allGather(message: String): ArrayBuffer[String] = {
Review comment:
Fair point; why not just `Seq`?
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