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https://issues.apache.org/jira/browse/HDFS-5746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13884886#comment-13884886
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Andrew Wang commented on HDFS-5746:
-----------------------------------
Thanks Colin, more comments:
* For the {{notificationSockets}} javadoc, I basically just wanted the
explanation you gave: it's a socketpair, where the loop listens on 1, clients
kick the loop by writing on 0.
* Can we verify the fix for racing {{sendCallback}} and {{toRemove}}? I think
we need to check that the fd being removed is in {{entries}} before doing
{{sendCallback}}. {{firstEntry}} also doesn't remove the entry from
{{toRemove}}, so it looks like this inf loops. {{pollFirstEntry}} instead?
* Maybe {{remove()}} should also return a boolean "success" value too, rather
than just swallowing an unknown socket.
Were these comments addressed?
{quote}
* Should doc that we only support one Handler per fd, it overwrites on add.
* Can add a Precondition check to make sure the lock is held in checkNotClosed
{quote}
ShortCircuitSharedMemorySegment:
* Flag constants would be more readable as "1<<63" and "1<<62" rather than 15
zeroes (I did verify though :))
* Comment in Slot constructor talks about incrementing a refcount, but that's
no longer happening there.
* No need to throw IOException in Slot constructor.
* Terminology: it seems like the "anchorable" flag means "is mlocked by DN and
can increment the refcount" and "anchor" is a refcount for "using mlocked
data". Renaming things would make this clearer, e.g. "lockable" for the flag,
and then "lockcount" for the count. IMO, incrementing an anchor is not a great
physical analogy :)
* How do we communicate the slot index between the DN and client? I see we keep
the slot address, but what we need to pass to the client is an index. Maybe
this is coming.
> add ShortCircuitSharedMemorySegment
> -----------------------------------
>
> Key: HDFS-5746
> URL: https://issues.apache.org/jira/browse/HDFS-5746
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, hdfs-client
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Fix For: 3.0.0
>
> Attachments: HDFS-5746.001.patch, HDFS-5746.002.patch,
> HDFS-5746.003.patch
>
>
> Add ShortCircuitSharedMemorySegment, which will be used to communicate
> information between the datanode and the client about whether a replica is
> mlocked.
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