Aidan Sadowski created COLLECTIONS-776:
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Summary: Wrapping PassiveExpiringMap in a SynchonizedMap breaks
expiration
Key: COLLECTIONS-776
URL: https://issues.apache.org/jira/browse/COLLECTIONS-776
Project: Commons Collections
Issue Type: Bug
Components: Collection
Affects Versions: 4.4
Environment: Java 8
Built on mac OS Catalina 10.15 using gradle 5.2.1 in Intellij
Reporter: Aidan Sadowski
The documentation for PassiveExpiringMap says "If you wish to use this map from
multiple threads concurrently, you must use appropriate synchronization. The
simplest approach is to wrap this map using
[{{Collections.synchronizedMap(Map)}}|https://docs.oracle.com/javase/7/docs/api/java/util/Collections.html?is-external=true#synchronizedMap-java.util.Map-].";
However, wrapping a PassiveExpiringMap in a Collections.synchronizedMap seems
to break the PassiveExpiringMap's expiration. Specifically, the operation
passiveExirpringMap.keySet() no longer removes expired entries prior to
returning (which it should, according to the PassiveExpiringMap doc).
I wrote this simple program to prove it. It puts a key into two
PassiveExpiringMaps with the same expiration policy of 15 seconds, one of which
is wrapped in a SyncronizedMap. Then it loops through the maps, calling
keySet() on them. The entry disappears from the unwrapped map after 15 seconds,
but NOT the wrapped map! Code and log output below.
{code:java}
import java.text.SimpleDateFormat;
import java.util.Collections;
import java.util.Date;
import java.util.Map;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import org.apache.commons.collections4.map.PassiveExpiringMap;
public class Main {
// unwrapped
static Map<String, String> unwrappedMap;
// wrapped
static Map<String, String> wrappedMap;
public static void main(String[] args) throws InterruptedException {
unwrappedMap = new PassiveExpiringMap<>(15, TimeUnit.SECONDS);
wrappedMap = Collections.synchronizedMap(new PassiveExpiringMap<>(15,
TimeUnit.SECONDS));
// Put something in the maps
String key = UUID.randomUUID().toString();
logWithTimestamp("Putting key " + key);
unwrappedMap.put(key, "");
wrappedMap.put(key, "");
// Check the map until the key has expired, sleeping 1 second between
checks
while (true) {
Set<String> keysInUnwrappedMap = unwrappedMap.keySet();
Set<String> keysInWrappedMap = wrappedMap.keySet();
logWithTimestamp("Keys in unwrapped map: " + String.join(", ",
keysInUnwrappedMap));
logWithTimestamp("Keys in wrapped map: " + String.join(", ",
keysInWrappedMap));
Thread.sleep(1000);
}
}
private static SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
private static void logWithTimestamp(String string) {
Date resultdate = new Date(System.currentTimeMillis());
System.out.println("[" + sdf.format(resultdate) + "] " + string);
}
}
{code}
{code:java}
[10:02:41] Putting key fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:41] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:41] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:42] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:42] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:43] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:43] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:44] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:44] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:45] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:45] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:46] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:46] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:47] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:47] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:48] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:48] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:49] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:49] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:50] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:50] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:51] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:51] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:52] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:52] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:53] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:53] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:54] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:54] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:55] Keys in unwrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:55] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:56] Keys in unwrapped map:
[10:02:56] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:57] Keys in unwrapped map:
[10:02:57] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:58] Keys in unwrapped map:
[10:02:58] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
[10:02:59] Keys in unwrapped map:
[10:02:59] Keys in wrapped map: fce9d058-8f13-4e6d-814e-90e03f575678
{code}
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