imaffe commented on issue #2019:
URL: https://github.com/apache/rocketmq/issues/2019#issuecomment-632930718
Sorry I didn't make it claer. Actually this is found in resetOffset():
```
public boolean resetOffset(long offset) {
MappedFile mappedFileLast = getLastMappedFile();
if (mappedFileLast != null) {
long lastOffset = mappedFileLast.getFileFromOffset() +
mappedFileLast.getWrotePosition();
long diff = lastOffset - offset;
final int maxDiff = this.mappedFileSize * 2;
if (diff > maxDiff)
return false;
}
ListIterator<MappedFile> iterator = this.mappedFiles.listIterator();
while (iterator.hasPrevious()) {
mappedFileLast = iterator.previous();
if (offset >= mappedFileLast.getFileFromOffset()) {
int where = (int) (offset % mappedFileLast.getFileSize());
mappedFileLast.setFlushedPosition(where);
mappedFileLast.setWrotePosition(where);
mappedFileLast.setCommittedPosition(where);
break;
} else {
iterator.remove();
}
}
return true;
}
```
and I saws deleteLastFile() actually deleted the file.
```
public void deleteLastMappedFile() {
MappedFile lastMappedFile = getLastMappedFile();
if (lastMappedFile != null) {
lastMappedFile.destroy(1000);
this.mappedFiles.remove(lastMappedFile);
log.info("on recover, destroy a logic mapped file " +
lastMappedFile.getFileName());
}
}
```
So it appears to me that when we remove a mappedFile from
`this.mappedFiles`，we actually want to delete the underlying file as well. I
thought if we use `iterator.remove()` without deleting the file, we lose the
reference to that file as well. (because this.mappedFiles are supposed to hold
the )
Otherwise it might be that we don't need to call `iterator.remove()`,
because I saw Java 8 doc
> (For CopyOnWriteList iterators)Mutation operations on iterators (remove,
set, and add) are not supported. These methods throw
UnsupportedOperationException. (which is a runtime exception)
Which seems weird to me. If that's true then the `iterator.remove()` is not
working at all.
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