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https://issues.apache.org/jira/browse/FLINK-7423?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124791#comment-16124791
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ASF GitHub Bot commented on FLINK-7423:
---------------------------------------
Github user XuPingyong commented on the issue:
https://github.com/apache/flink/pull/4525
@greghogan， if the object passed to nextRecord may be reused internally by
the InputFormat, do the similar cases need to be re-considered?
In `DataSourceTask.java`:
OT reuse = serializer.createInstance();
// as long as there is data to read
while (!this.taskCanceled && !format.reachedEnd()) {
OT returned;
if ((returned = format.nextRecord(reuse)) != null) {
output.collect(returned);
}
}
And in many batch drivers:
final MutableObjectIterator<T> in = taskContext.getInput(0);
T value = serializer.createInstance();
while (running && (value = in.next(value)) != null) {
.......
}
In my opinion:
1. `Null` records are meaningless, but `null` is meaningful for input
or format which means the end. If a user only call `InputFormat#nextRecord`
without `InputFormat#reachedEnd`, only `null` can be returned.
2. The returned object of `InputFormat#nextRecord` should not need to
be considered that it may be passed again. If a immutable object is returned,
an exception will be thrown when it is reused again in
`InputFormat#nextRecord`.
@greghogan, could you please offer some cases that the object passed to
nextRecord can be reused internally by the InputFormat? Thanks.
> Always reuse an instance to get elements from the inputFormat
> ---------------------------------------------------------------
>
> Key: FLINK-7423
> URL: https://issues.apache.org/jira/browse/FLINK-7423
> Project: Flink
> Issue Type: Bug
> Components: DataStream API
> Reporter: Xu Pingyong
> Assignee: Xu Pingyong
>
> In InputFormatSourceFunction.java:
> {code:java}
> OUT nextElement = serializer.createInstance();
> while (isRunning) {
> format.open(splitIterator.next());
> // for each element we also check if cancel
> // was called by checking the isRunning flag
> while (isRunning && !format.reachedEnd()) {
> nextElement =
> format.nextRecord(nextElement);
> if (nextElement != null) {
> ctx.collect(nextElement);
> } else {
> break;
> }
> }
> format.close();
> completedSplitsCounter.inc();
> if (isRunning) {
> isRunning = splitIterator.hasNext();
> }
> }
> {code}
> the format may return other element or null when nextRecord, that will may
> cause exception.
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