kamaci commented on a change in pull request #6662: Double-checked locking bugs
URL: https://github.com/apache/incubator-druid/pull/6662#discussion_r237839855
##########
File path:
aws-common/src/main/java/org/apache/druid/common/aws/LazyFileSessionCredentialsProvider.java
##########
@@ -32,14 +32,10 @@ public
LazyFileSessionCredentialsProvider(AWSCredentialsConfig config)
this.config = config;
}
- private FileSessionCredentialsProvider getUnderlyingProvider()
+ private synchronized FileSessionCredentialsProvider getUnderlyingProvider()
Review comment:
Here is the implementation with reference to _Effective Java, Second Edition
Item 71: Use lazy initialization judiciously_:
```java
private final AWSCredentialsConfig config;
/* The field is declared volatile in order to ensure safe publication of
the object
without worrying about final modifiers on the fields of the created
object */
@Nullable
private volatile FileSessionCredentialsProvider provider;
public LazyFileSessionCredentialsProvider(AWSCredentialsConfig config)
{
this.config = config;
}
//FileSessionCredentialsProvider is safely initialized because it contains
a final field sessionCredentials.
private FileSessionCredentialsProvider getUnderlyingProvider() {
FileSessionCredentialsProvider syncedProvider = provider;
if (syncedProvider == null) {
synchronized (config) {
syncedProvider = provider;
if (syncedProvider == null) {
syncedProvider = new
FileSessionCredentialsProvider(config.getFileSessionCredentials());
provider = syncedProvider;
}
}
}
return syncedProvider;
}
```
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