[GitHub] [skywalking] wu-sheng commented on a change in pull request #5523: Provide metrics APIs for agent plugin

[GitBox <gi...@apache.org>]

wu-sheng commented on a change in pull request #5523:
URL: https://github.com/apache/skywalking/pull/5523#discussion_r491692763



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File path: docs/en/guides/Java-Plugin-Development-Guide.md
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@@ -443,3 +443,44 @@ Please follow there steps:
 1. Send the pull request and ask for review. 
 1. The plugin committers approve your plugins, plugin CI-with-IT, e2e and plugin tests passed.
 1. The plugin accepted by SkyWalking. 
+
+### Plugin Meter reporter
+Java agent also supports customize meter report to backend. We provide Java Agent Core level API such as [Application Toolkit meter](../setup/service-agent/java-agent/Application-toolkit-meter.md).
+
+* `Counter` API represents a single monotonically increasing counter, automatic collect data and report to backend.
+```java
+import org.apache.skywalking.apm.agent.core.meter.MeterFactory;
+
+Counter counter = MeterFactory.counter(meterName).tag("tagKey", "tagValue").mode(Counter.Mode.INCREMENT).build();
+counter.increment(1d);
+```
+1. `MeterFactory.counter` Create a new counter builder with the meter name.
+1. `Counter.Builder.tag(String key, String value)` Mark a tag key/value pair.
+1. `Counter.Builder.mode(Counter.Mode mode)` Change the counter mode, `RATE` mode means reporting rate to the backend.
+1. `Counter.Builder.build()` Build a new `Counter` which is collected and reported to the backend.
+1. `Counter.increment(double count)` Increment count to the `Counter`, It could be a positive/negative value.

Review comment:
       I feel accepting the `negative` value is conflicting with the definition of the counter. `a single monotonically increasing counter`. 
   
   Please recheck.




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