TokenMetaData.getPendingRangesMM() is unnecessarily synchronized
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Key: CASSANDRA-1370
URL: https://issues.apache.org/jira/browse/CASSANDRA-1370
Project: Cassandra
Issue Type: Improvement
Components: Core
Affects Versions: 0.6.4
Reporter: Jason Fager
Priority: Minor
TokenMetaData.getPendingRangesMM() is currently synchronized to avoid a race
condition where multiple threads might create a multimap for the given table.
However, the pendingRanges instance variable that's the subject of the race
condition is already a ConcurrentHashMap, and the race condition can be avoided
by using putIfAbsent, leaving the case where the table's map is already
initialized lock-free:
private Multimap<Range, InetAddress> getPendingRangesMM(String table)
{
Multimap<Range, InetAddress> map = pendingRanges.get(table);
if (map == null)
{
map = HashMultimap.create();
Multimap<Range, InetAddress> fasterHorse
= pendingRanges.putIfAbsent(table, map);
if(fasterHorse != null) {
//another thread beat us to creating the map, oh well.
map = fasterHorse;
}
}
return map;
}
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