FrankChen021 commented on PR #13286:
URL: https://github.com/apache/druid/pull/13286#issuecomment-1299470197
> >
>
> I realized that there are two conditions that may lead to `NPE` in the
access identifier
>
> 1. The `identifier` may be modified by the `emitMetric` thread. Since
identifier is a common object attribute, it may not be visible to the
`PrometheusPushGatewayEmitter` thread
> 2. `emitMetric` is not called in advance, but the identifier is accessed.
Yeah, the 2nd case is the reason.
The check logic in `pushMetric` and `flush` is a little bit chaos. Could you
improve it by putting all checks together like:
```java
private void pushMetric()
{
if ( pushGateway == null || identifier == null) {
return ;
}
...
```
Another point(not relevant to this PR) is, checking if namespace is null is
meaningless since it's guaranteed it won't be null.
```java
@JsonCreator
public PrometheusEmitterConfig(
...
)
{
...
this.namespace = namespace != null ? namespace : "druid";
```
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