virajjasani commented on a change in pull request #3148:
URL: https://github.com/apache/hadoop/pull/3148#discussion_r659595214
##########
File path:
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java
##########
@@ -2272,19 +2274,11 @@ public int getActiveTransferThreadCount() {
void incrDatanodeNetworkErrors(String host) {
metrics.incrDatanodeNetworkErrors();
- /*
- * Synchronizing on the whole cache is a big hammer, but since it's only
- * accumulating errors, it should be ok. If this is ever expanded to
include
- * non-error stats, then finer-grained concurrency should be applied.
- */
- synchronized (datanodeNetworkCounts) {
- try {
- final Map<String, Long> curCount = datanodeNetworkCounts.get(host);
- curCount.put("networkErrors", curCount.get("networkErrors") + 1L);
- datanodeNetworkCounts.put(host, curCount);
- } catch (ExecutionException e) {
- LOG.warn("failed to increment network error counts for host: {}",
host);
- }
+ try {
+ datanodeNetworkCounts.get(host).compute(NETWORK_ERRORS,
+ (key, errors) -> errors == null ? null : errors + 1L);
Review comment:
Map.compute() is just replacement of below code (and ConcurrentHashMap
does it atomically):
```
* <pre> {@code
* V oldValue = map.get(key);
* V newValue = remappingFunction.apply(key, oldValue);
* if (oldValue != null ) {
* if (newValue != null)
* map.put(key, newValue);
* else
* map.remove(key);
* } else {
* if (newValue != null)
* map.put(key, newValue);
* else
* return null;
* }
* }</pre>
```
errors will ideally never be null because it is defined as `0L` here:
```
datanodeNetworkCounts =
CacheBuilder.newBuilder()
.maximumSize(dncCacheMaxSize)
.build(new CacheLoader<String, Map<String, Long>>() {
@Override
public Map<String, Long> load(String key) throws Exception {
final Map<String, Long> ret = new HashMap<String, Long>();
ret.put("networkErrors", 0L);
return ret;
}
});
```
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