asdf2014 commented on a change in pull request #6868: Fix deadlock in
DruidStatement & DruidConnection
URL: https://github.com/apache/incubator-druid/pull/6868#discussion_r249639199
##########
File path: sql/src/main/java/org/apache/druid/sql/avatica/DruidConnection.java
##########
@@ -53,25 +54,29 @@
private final AtomicInteger statementCounter = new AtomicInteger();
private final AtomicReference<Future<?>> timeoutFuture = new
AtomicReference<>();
- @GuardedBy("statements")
- private final Map<Integer, DruidStatement> statements;
+ // Typically synchronized by connectionLock, except in one case: the onClose
function passed
+ // into DruidStatements contained by the map.
+ private final ConcurrentMap<Integer, DruidStatement> statements;
- @GuardedBy("statements")
+ @GuardedBy("connectionLock")
Review comment:
Thanks for explaining this @gianm @zhaojiandong . I mean we shouldn't remove
the `@GuardedBy("connectionLock")` from `statements` because the `statements`
is not always synchronized by `connectionLock` and the CI fails, which is
unreasonable. In addition, putting a `@GuardedBy` on `connectionLock` is also
not necessary. If this is done, it means that we should have the
`connectionLock` lock object when we use `connectionLock`, in fact it cannot
achieve the purpose that we should own the `connectionLock` when using
`statements`. So, i think there is a better way to solve this situation by
adding a `@SuppressWarnings("FieldAccessNotGuarded")` annotation to the
`Runnable#run` method, or adding a `// noinspection FieldAccessNotGuarded`
comment to the `statements.remove(statementId)` caluse, which will suppress
this check and make CI happy.
```java
@GuardedBy("connectionLock")
private final ConcurrentMap<Integer, DruidStatement> statements;
private final Object connectionLock = new Object();
public DruidStatement createStatement(SqlLifecycleFactory
sqlLifecycleFactory)
{
// ...
final DruidStatement statement = new DruidStatement(
// ...
() -> {
// noinspection FieldAccessNotGuarded
statements.remove(statementId);
}
);
// ...
}
```
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