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Prevent the runtime attachment from launching multiple times #409

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Jul 26, 2022
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Prevent the runtime attachment from launching multiple times #409

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7 changes: 7 additions & 0 deletions .../runtime-attach-core/src/main/java/io/opentelemetry/contrib/attach/CoreRuntimeAttach.java
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@ public final class CoreRuntimeAttach {

private final String agentJarResourceName;

private boolean runtimeAttachmentRequested;

/**
* Creates a new {@code DistroRuntimeAttach} from the resource name of the agent jar.
*
Expand All @@ -37,6 +39,11 @@ public void attachJavaagentToCurrentJVM() {
return;
}

if (runtimeAttachmentRequested) {
return;
}
runtimeAttachmentRequested = true;
Comment on lines +42 to +45
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I'm just wondering, what kind of situations are we trying to prevent here? A simple duplicated line of code? Or runtime attach being called from completely different places in the application? Would it make sense to print out a warning with a stack trace to help pinpoint the unnecessary invocations?

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This PR aims to prevent the runtime attachment from being invoked several times from the main method. If a runtime attachment is invoked while another runtime attachment is in progress and not finished, I am not sure about the result with JVM attachment mechanism. The instrumentation might not be correctly installed.

Would it make sense to print out a warning with a stack trace to help pinpoint the unnecessary invocations?

Nothing is displayed to be consistent with the current display policy. First, this type of message was reported with a debug log. After, the warning log messages were replaced with System.err.println and the debug messages removed. Perhaps it may be worth rediscussing this display policy.

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If a runtime attachment is invoked while another runtime attachment is in progress and not finished

Again, is that a valid scenario? Don't we already have a check that verifies that only the main thread can call this method?
Otherwise, if a concurrent scenario is possible, then this code needs to be thread safe (use AtomicBoolean instead).

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Don't we already have a check that verifies that only the main thread can call this method?
Otherwise, if a concurrent scenario is possible, then this code needs to be thread safe (use AtomicBoolean instead).

The scenario is about two runtime attachments requested from the main thread since the new check is after the main thread check.

Again, is that a valid scenario?

I have not today enough knowledge about the Attach Listener JVM thread implementation. I would prefer to stop the things ealier because it is not the kind of issue I would like to debug. We can close this PR on OTel if you prefer.

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I would prefer to stop the things ealier because it is not the kind of issue I would like to debug.

👍

We can close this PR on OTel if you prefer.

No, I approve of this PR, I think this kind of check definitely makes sense. I was wondering whether this was motivated by a real use case, and if so, what kind of issue it was.


AgentFileProvider agentFileProvider = new AgentFileProvider(agentJarResourceName);

File javaagentFile = agentFileProvider.getAgentFile();
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