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Update debugging doc (#1296)

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Trask Stalnaker 2020-10-01 11:13:31 -07:00 committed by GitHub
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docs/contributing/debugging.md
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@ -1,12 +1,9 @@
### Debugging
Debugging java agent can be a challenging task since some instrumentation
code is directly inlined into target classes and debugger is
usually not attached early enough to activate breakpoints
in agent initialization code (`OpenTelemetryAgent`, `AgentInitializer`, `AgentInstaller`,
`TracerInstaller`, etc.).
code is directly inlined into target classes.
#### Advice methods and agent initialization
#### Advice methods
Breakpoints do not work in advice methods, because their code is directly inlined
by ByteBuddy into the target class. It is good to keep these methods as small as possible.
@ -24,11 +21,17 @@ System.out.println()
Thread.dumpStack()
```
#### Enable debugger
#### Agent initialization code
If you want to debug agent initialization code (e.g. `OpenTelemetryAgent`, `AgentInitializer`,
`AgentInstaller`, `TracerInstaller`, etc.) then it's important to specify the `-agentlib:` JVM arg
before the `-javaagent:` JVM arg and use `suspend=y` (see full example below).
#### Enabling debugging
The following example shows remote debugger configuration. The breakpoints
should work in any code except ByteBuddy advice methods and agent initialization code.
should work in any code except ByteBuddy advice methods.
```bash
java -javaagent:opentelemetry-javaagent-<version>-all.jar -jar -agentlib:jdwp="transport=dt_socket,server=y,suspend=y,address=5000" app.jar
java -agentlib:jdwp="transport=dt_socket,server=y,suspend=y,address=5000" -javaagent:opentelemetry-javaagent-<version>-all.jar -jar app.jar
```