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Posted to commits@druid.apache.org by GitBox <gi...@apache.org> on 2022/10/29 12:36:49 UTC
[GitHub] [druid] 599166320 opened a new pull request, #13286: PrometheusEmitter NullPointerException fix
599166320 opened a new pull request, #13286:
URL: https://github.com/apache/druid/pull/13286
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Fixes [#13285](https://github.com/apache/druid/issues/13285).
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### Description
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PrometheusEmitter NullPointerException fix
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<hr>
##### Key changed/added classes in this PR
* `PrometheusEmitter`
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[GitHub] [druid] FrankChen021 commented on pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
FrankChen021 commented on PR #13286:
URL: https://github.com/apache/druid/pull/13286#issuecomment-1300427015
Thanks for the cleanup.
We also need to remove the `Nullable` annotation from the `namespace` since it won't be null at all.
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[GitHub] [druid] FrankChen021 merged pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
FrankChen021 merged PR #13286:
URL: https://github.com/apache/druid/pull/13286
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[GitHub] [druid] cryptoe commented on a diff in pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
cryptoe commented on code in PR #13286:
URL: https://github.com/apache/druid/pull/13286#discussion_r1008699290
##########
extensions-contrib/prometheus-emitter/src/main/java/org/apache/druid/emitter/prometheus/PrometheusEmitter.java:
##########
@@ -57,7 +58,7 @@ public class PrometheusEmitter implements Emitter
private HTTPServer server;
private PushGateway pushGateway;
- private String identifier;
+ private volatile String identifier;
Review Comment:
Curious to understand the race here!
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[GitHub] [druid] 599166320 commented on a diff in pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
599166320 commented on code in PR #13286:
URL: https://github.com/apache/druid/pull/13286#discussion_r1008710907
##########
extensions-contrib/prometheus-emitter/src/main/java/org/apache/druid/emitter/prometheus/PrometheusEmitter.java:
##########
@@ -57,7 +58,7 @@ public class PrometheusEmitter implements Emitter
private HTTPServer server;
private PushGateway pushGateway;
- private String identifier;
+ private volatile String identifier;
Review Comment:
The existence of multiple threads calling emitMetric will modify the `identifier`. Even if the `identifier` is modified countless times, there will always be only one result, which is an `idempotent design`.
Currently only the thread of `PrometheusPushGatewayEmitter` will read the value of `identifier`. In order to guarantee the visibility of the reading thread, I use volatile to decorate the `identifier`.
In addition, there is an inefficient way to use LinkedBlockingQueue to achieve safe publishing. This is how `InfluxdbEmitter` is implemented.
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[GitHub] [druid] 599166320 commented on pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
599166320 commented on PR #13286:
URL: https://github.com/apache/druid/pull/13286#issuecomment-1296093336
>
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.
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[GitHub] [druid] FrankChen021 commented on pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
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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[GitHub] [druid] FrankChen021 commented on pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
FrankChen021 commented on PR #13286:
URL: https://github.com/apache/druid/pull/13286#issuecomment-1296085414
Thanks for the fix.
From the assignment statement, I don't understand how could `identifier` be null?
```java
identifier = (userDims.get("task") == null ? metricEvent.getHost() : (String) userDims.get("task"));
```
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[GitHub] [druid] 599166320 commented on pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
599166320 commented on PR #13286:
URL: https://github.com/apache/druid/pull/13286#issuecomment-1300421150
@FrankChen021 I debugged. If `druid.emitter.prometheus.namespace=xxx` is not configured, the value of `namespace` will be at least `druid`. In order to make the code more concise and clear, I have deleted meaningless judgments
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[GitHub] [druid] cryptoe commented on a diff in pull request #13286: PrometheusEmitter NullPointerException fix
Posted by GitBox <gi...@apache.org>.
cryptoe commented on code in PR #13286:
URL: https://github.com/apache/druid/pull/13286#discussion_r1008699290
##########
extensions-contrib/prometheus-emitter/src/main/java/org/apache/druid/emitter/prometheus/PrometheusEmitter.java:
##########
@@ -57,7 +58,7 @@ public class PrometheusEmitter implements Emitter
private HTTPServer server;
private PushGateway pushGateway;
- private String identifier;
+ private volatile String identifier;
Review Comment:
Curious to understand the race here.
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