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https://issues.apache.org/jira/browse/HDFS-7276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14192767#comment-14192767
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Tsz Wo Nicholas Sze commented on HDFS-7276:
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> I don't see any case where this would deadlock if we used notify rather than
> notifyAll. ...
Here is a deadlock example. Suppose the limit=n, the allocation count=n, T1 ...
Tn are threads allocated a buffer but not yet released.
# Two new threads Tn+1 and Tn+2 call allocate, both have to wait.
# T1 releases a buffer; count becomes n-1; T1 calls notify but not notifyAll;
only Tn+1 wakes up.
# Before Tn+1 is scheduled to run, T2 ... Tn are executed and release a buffer;
they won't call notify since count < limit; count eventually becomes 0.
# Now, Tn+1 is scheduled to run and allocates a buffer; count becomes 1
# Tn+1 comes back and releases the buffer, it also won't call notify since
count < limit; count becomes 0
# Tn+2 will wait forever if there is no more allocate calls.
> Limit the number of byte arrays used by DFSOutputStream
> -------------------------------------------------------
>
> Key: HDFS-7276
> URL: https://issues.apache.org/jira/browse/HDFS-7276
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
> Attachments: h7276_20141021.patch, h7276_20141022.patch,
> h7276_20141023.patch, h7276_20141024.patch, h7276_20141027.patch,
> h7276_20141027b.patch, h7276_20141028.patch, h7276_20141029.patch,
> h7276_20141029b.patch, h7276_20141030.patch, h7276_20141031.patch
>
>
> When there are a lot of DFSOutputStream's writing concurrently, the number of
> outstanding packets could be large. The byte arrays created by those packets
> could occupy a lot of memory.
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