Add ANR docs (#787)

* order alphabeticaly

* add docs for anr

* spotless

android-agent/build.gradle.kts

@@ -14,12 +14,12 @@ dependencies {
 
     // Default instrumentations:
     api(project(":instrumentation:activity"))
-    api(project(":instrumentation:fragment"))
-    api(project(":instrumentation:crash"))
-    api(project(":instrumentation:startup"))
-    api(project(":instrumentation:slowrendering"))
     api(project(":instrumentation:anr"))
+    api(project(":instrumentation:crash"))
+    api(project(":instrumentation:fragment"))
     api(project(":instrumentation:network"))
+    api(project(":instrumentation:slowrendering"))
+    api(project(":instrumentation:startup"))
 }
 
 extra["pomName"] = "OpenTelemetry Android Agent"

instrumentation/anr/README.md

@@ -0,0 +1,30 @@
+
+# ANR (Application Not Responding) Instrumentation
+
+Status: experimental
+
+The ANR (Application Not Responding) instrumentation helps to detect
+when an application becomes unresponsive. This instrumentation functions
+by polling the UI thread once every second, verifying that the main UI
+thread is still active. If 5 consecutive checks fail, then an ANR condition
+has occurred, and telemetry will be generated.
+
+The ANR instrumentation is only active when the application is in the
+foreground.
+
+## Telemetry
+
+This instrumentation produces the following telemetry:
+
+### ANR
+
+* Type: Span
+* Name: `ANR`
+* Description: This zero-duration span is created when this instrumentation detects an ANR.
+* Status: `ERROR` (always)
+* Attributes:
+  * `exception.stacktrace`: A string representation of the call stack of the main thread at the time of the ANR.
+    ([see semconv here](https://github.com/open-telemetry/semantic-conventions/blob/0b3babde7ff9f74b03a1a49adcdb319354d47d85/docs/attributes-registry/exception.md#exception-stacktrace))
+
+Note: This instrumentation supports additional user-configurable `AttributeExtractors` that
+may set additional attributes from the given `StackTraceElement[]`.