gianm commented on a change in pull request #6898: Prohibit assigning
concurrent maps into Map-typed variables and fields and fix a race condition in
CoordinatorRuleManager
URL: https://github.com/apache/incubator-druid/pull/6898#discussion_r251258049
##########
File path:
indexing-service/src/main/java/org/apache/druid/indexing/common/Counters.java
##########
@@ -19,54 +19,31 @@
package org.apache.druid.indexing.common;
-import com.google.common.util.concurrent.AtomicDouble;
-
-import javax.annotation.Nullable;
import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.BinaryOperator;
+import java.util.concurrent.atomic.AtomicLong;
-public class Counters
+public final class Counters
{
- private final ConcurrentMap<String, AtomicInteger> intCounters = new
ConcurrentHashMap<>();
- private final ConcurrentMap<String, AtomicDouble> doubleCounters = new
ConcurrentHashMap<>();
- private final ConcurrentMap<String, AtomicReference> objectCounters = new
ConcurrentHashMap<>();
-
- public int increment(String key, int val)
+ public static <K> int incrementAndGetInt(ConcurrentHashMap<K, AtomicInteger>
counters, K key)
{
- return intCounters.computeIfAbsent(key, k -> new
AtomicInteger()).addAndGet(val);
+ // get() before computeIfAbsent() is an optimization to avoid locking in
computeIfAbsent() if not needed.
Review comment:
Any idea why ConcurrentHashMap does not already employ an optimization like
this?
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