dosubot[bot] commented on issue #2618:
URL:
https://github.com/apache/incubator-hugegraph/issues/2618#issuecomment-2270327041
<!-- Answer -->
To ensure that `storeEventListener` is not registered multiple times in
`CachedSystemTransactionV2` and `CachedGraphTransaction`, you can use a
`ThreadLocal` variable to keep track of whether the listener has already been
registered for the current thread. Here is an example of how you can modify the
`listenChanges` method to achieve this:
```java
public final class CachedGraphTransaction extends GraphTransaction {
private static final ThreadLocal<Boolean> listenerRegistered =
ThreadLocal.withInitial(() -> false);
private void listenChanges() {
if (listenerRegistered.get()) {
return;
}
// Listen store event: "store.init", "store.clear", ...
Set<String> storeEvents = ImmutableSet.of(Events.STORE_INIT,
Events.STORE_CLEAR,
Events.STORE_TRUNCATE);
this.storeEventListener = event -> {
if (storeEvents.contains(event.name())) {
LOG.debug("Graph {} clear graph cache on event '{}'",
this.graph(), event.name());
this.clearCache(null, true);
return true;
}
return false;
};
this.store().provider().listen(this.storeEventListener);
// Listen cache event: "cache"(invalid cache item)
this.cacheEventListener = event -> {
LOG.debug("Graph {} received graph cache event: {}",
this.graph(), event);
Object[] args = event.args();
E.checkArgument(args.length > 0 && args[0] instanceof String,
"Expect event action argument");
if (Cache.ACTION_INVALID.equals(args[0])) {
event.checkArgs(String.class, HugeType.class, Object.class);
HugeType type = (HugeType) args[1];
if (type.isVertex()) {
// Invalidate vertex cache
Object arg2 = args[2];
if (arg2 instanceof Id) {
Id id = (Id) arg2;
this.verticesCache.invalidate(id);
} else if (arg2 != null && arg2.getClass().isArray()) {
int size = Array.getLength(arg2);
for (int i = 0; i < size; i++) {
Object id = Array.get(arg2, i);
E.checkArgument(id instanceof Id,
"Expect instance of Id in array,
" +
"but got '%s'", id.getClass());
this.verticesCache.invalidate((Id) id);
}
} else {
E.checkArgument(false,
"Expect Id or Id[], but got: %s",
arg2);
}
} else if (type.isEdge()) {
/*
* Invalidate edge cache via clear instead of invalidate
* because of the cacheKey is QueryId not EdgeId
*/
// this.edgesCache.invalidate(id);
this.edgesCache.clear();
}
return true;
} else if (Cache.ACTION_CLEAR.equals(args[0])) {
event.checkArgs(String.class, HugeType.class);
HugeType type = (HugeType) args[1];
this.clearCache(type, false);
return true;
}
return false;
};
EventHub graphEventHub = this.params().graphEventHub();
if (!graphEventHub.containsListener(Events.CACHE)) {
graphEventHub.listen(Events.CACHE, this.cacheEventListener);
}
listenerRegistered.set(true);
}
private void unlistenChanges() {
// Unlisten store event
this.store().provider().unlisten(this.storeEventListener);
// Unlisten cache event
EventHub graphEventHub = this.params().graphEventHub();
graphEventHub.unlisten(Events.CACHE, this.cacheEventListener);
listenerRegistered.set(false);
}
// Other methods...
}
```
This code uses a `ThreadLocal` variable `listenerRegistered` to keep track
of whether the listeners have been registered for the current thread. The
`listenChanges` method checks this variable before registering the listeners,
and the `unlistenChanges` method resets it when the listeners are unregistered
<sup>[[1]](https://github.com/apache/incubator-hugegraph/blob/master/hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/cache/CachedGraphTransaction.java)</sup>.
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