wu-sheng commented on a change in pull request #5523:
URL: https://github.com/apache/skywalking/pull/5523#discussion_r491692763
##########
File path: docs/en/guides/Java-Plugin-Development-Guide.md
##########
@@ -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.
##########
File path:
apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/meter/builder/Histogram.java
##########
@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package org.apache.skywalking.apm.agent.core.meter.builder;
+
+import java.util.List;
+
+/**
+ * Similar to a histogram, a summary sample observations (usual things like
request durations and response sizes).
Review comment:
What does this `similar to a histogram` mean? Isn't this a histogram
already?
##########
File path:
apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/meter/builder/Histogram.java
##########
@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package org.apache.skywalking.apm.agent.core.meter.builder;
+
+import java.util.List;
+
+/**
+ * Similar to a histogram, a summary sample observations (usual things like
request durations and response sizes).
+ * While it also provides a total count of observations and a sum of all
observed values, it calculates configurable quartiles over a sliding time
window.
Review comment:
Are you copying this from Prometheus or somewhere? Also, at the same
time, `HistogramImpl`'s comments don't make sense.
##########
File path:
apm-application-toolkit/apm-toolkit-meter/src/main/java/org/apache/skywalking/apm/toolkit/meter/impl/CounterImpl.java
##########
@@ -51,30 +48,13 @@ public void increment(double count) {
/**
* Get count value
*/
- public double get() {
+ public double getCount() {
Review comment:
Why change this name? But such as in `GuageImpl`, still, use `get`?
Seems inconsistent to me.
##########
File path: docs/en/guides/Java-Plugin-Development-Guide.md
##########
@@ -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
Review comment:
```suggestion
### Plugin Meter Plugin
```
##########
File path: docs/en/guides/Java-Plugin-Development-Guide.md
##########
@@ -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).
Review comment:
```suggestion
Java agent plugin could use meter APIs to collect the metrics for backend
analysis.
```
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