leventov commented on a change in pull request #6662: Double-checked locking
bugs
URL: https://github.com/apache/incubator-druid/pull/6662#discussion_r237098326
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File path:
aws-common/src/main/java/org/apache/druid/common/aws/LazyFileSessionCredentialsProvider.java
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@@ -32,14 +32,10 @@ public
LazyFileSessionCredentialsProvider(AWSCredentialsConfig config)
this.config = config;
}
- private FileSessionCredentialsProvider getUnderlyingProvider()
+ private synchronized FileSessionCredentialsProvider getUnderlyingProvider()
Review comment:
@gianm general suggestion looks good.
1) We could still skip volatile when the initialized object is obviously
immutable, such as a String or an immutable collection.
2) Even with volatile, introducing local variable is more accurate
performance-wise and should be done.
> If that is right, then to get guaranteed safe initialization of an entire
class, all fields should be final (or volatile).
Correction - volatile on the initialized object's fields does *not*
guarantee you anything here. In some sense, `volatile` is *less strong* than
`final`. See
https://shipilev.net/blog/2016/close-encounters-of-jmm-kind/#wishful-volatiles-are-finals
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