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HBASE-15478 add comments to syncRunnerIndex handling explaining constraints on possible values. 

Signed-off-by: zhangduo <zhangduo@apache.org>
This commit is contained in:
Sean Busbey 2016-03-17 15:22:07 -05:00
parent 64204b96c1
commit f48c92d143
1 changed files with 11 additions and 2 deletions
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13
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/FSHLog.java
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@ -1785,10 +1785,19 @@ public class FSHLog implements WAL {
// If not a batch, return to consume more events from the ring buffer before proceeding;
// we want to get up a batch of syncs and appends before we go do a filesystem sync.
if (!endOfBatch || this.syncFuturesCount <= 0) return;
// Below expects that the offer 'transfers' responsibility for the outstanding syncs to
// the syncRunner. We should never get an exception in here.
// syncRunnerIndex is bound to the range [0, Integer.MAX_INT - 1] as follows:
// * The maximum value possible for syncRunners.length is Integer.MAX_INT
// * syncRunnerIndex starts at 0 and is incremented only here
// * after the increment, the value is bounded by the '%' operator to [0, syncRunners.length),
// presuming the value was positive prior to the '%' operator.
// * after being bound to [0, Integer.MAX_INT - 1], the new value is stored in syncRunnerIndex
// ensuring that it can't grow without bound and overflow.
// * note that the value after the increment must be positive, because the most it could have
// been prior was Integer.MAX_INT - 1 and we only increment by 1.
this.syncRunnerIndex = (this.syncRunnerIndex + 1) % this.syncRunners.length;
try {
// Below expects that the offer 'transfers' responsibility for the outstanding syncs to
// the syncRunner. We should never get an exception in here.
this.syncRunners[this.syncRunnerIndex].offer(sequence, this.syncFutures,
this.syncFuturesCount);
} catch (Exception e) {