Documentation for -XX:[+|-]EnableDynamicAgentLoading #1174

Sreekala-Gopakumar · 2023-09-20T06:24:29Z

#1140

Created a new topic for the -XX:[+|-]EnableDynamicAgentLoading option Updated the related topics.

Closes #1140
Signed-off-by: Sreekala Gopakumar sreekala.gopakumar@ibm.com

Sreekala-Gopakumar · 2023-09-20T06:41:28Z

Jenkins doc stage

pshipton · 2023-09-20T12:06:12Z

Jenkins doc stage

Sreekala-Gopakumar · 2023-09-20T13:16:33Z

@JasonFengJ9 - I have updated the documents. Please check and confirm. Thanks!

JasonFengJ9

@Sreekala-Gopakumar I made a few clarifications, please let me know if you have further questions.

JasonFengJ9 · 2023-09-21T01:21:28Z

docs/xxenabledynamicagentloading.md

@@ -0,0 +1,60 @@
+<!--
+* Copyright (c) 2017, 2023 IBM Corp. and others


Suggested change

* Copyright (c) 2017, 2023 IBM Corp. and others

* Copyright (c) 2023, 2023 IBM Corp. and others

As per the Contribution guidelines, copyright dates are not changed, even for a new topic; the dates refer to the complete documentation set, not to individual files and so should be the same in all topics.

https://github.com/eclipse-openj9/openj9-docs/blob/master/CONTRIBUTING.md#style-guidelines

JasonFengJ9 · 2023-09-21T01:26:50Z

docs/xxenabledynamicagentloading.md

+
+You can disable the dynamic loading of the agents into a VM after startup with the `-XX:-EnableDynamicAgentLoading` option.
+
+![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java&trade; 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option and the same agents were not loaded at startup by using the [command-line options](interface_jvmti.md#overview):


Suggested change

![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java™ 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option and the same agents were not loaded at startup by using the [command-line options](interface_jvmti.md#overview):

![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java™ 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option and the same agents were not loaded before at startup by using the [command-line options](interface_jvmti.md#overview) or an earlier dynamical loading, i.e., the warnings are only issued once even if it is dynamically loaded multiple times:

@JasonFengJ9 - If the agents are loaded dynamically into a running VM after startup after specifying the -XX:+EnableDynamicAgentLoading option, but the same agents were loaded before, the warnings will be issued?

the warnings are only issued once even if it is dynamically loaded multiple times:

I am not clear about this. if an agent is loaded without the XX:+EnableDynamicAgentLoading option multiple times. then won't the warnings be issued each time that agent is loaded?

Also, if the agent was loaded at startup with the command-line option or through dynamic loading (with the XX:+EnableDynamicAgentLoading option), then if that same agent is dynamically loaded again but without the XX:+EnableDynamicAgentLoading option, then the warning will be issued, right?

If the agents are loaded dynamically into a running VM after startup after specifying the -XX:+EnableDynamicAgentLoading option, but the same agents were loaded before, the warnings will be issued?

If -XX:+EnableDynamicAgentLoading is specified which is only possible at the VM startup command line options, there will be NO warnings always.

the warnings are only issued once even if it is dynamically loaded multiple times:

I am not clear about this. if an agent is loaded without the XX:+EnableDynamicAgentLoading option multiple times. then won't the warnings be issued each time that agent is loaded?

The warnings only appear once for the same agent when -XX:+EnableDynamicAgentLoading is not specified.

Also, if the agent was loaded at startup with the command-line option or through dynamic loading (with the XX:+EnableDynamicAgentLoading option), then if that same agent is dynamically loaded again but without the XX:+EnableDynamicAgentLoading option, then the warning will be issued, right?

Note that -XX:+EnableDynamicAgentLoading is a JVM startup command line option and affects all agent loading afterwards, i.e., if it is set at startup, all agents dynamically loaded regardless of their names/paths are considered approved by the application owner, and no warnings will be issued.

JasonFengJ9 · 2023-09-21T01:32:20Z

docs/xxenabledynamicagentloading.md

+WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
+WARNING: Dynamic loading of agents will be disallowed by default in a future release
+```
+AIX&reg; systems cannot detect whether an agent library was previously loaded at startup or not. Therefore, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the agent was loaded through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)


Suggested change

AIX® systems cannot detect whether an agent library was previously loaded at startup or not. Therefore, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the agent was loaded through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)

AIX® systems cannot detect whether an agent library was previously loaded or not if the library was loaded through a different name and path. Therefore, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the agent was loaded through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. If a library is loaded with the same name or absolute path multiple times, OpenJ9 JVM can detect that and only issue one warning message which is not AIX-specific capability. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)

@JasonFengJ9 - What do you mean by "only issue one warning message which is not AIX-specific capability"?

...the warnings are issued when an agent is loaded dynamically through the Attach API (VirtualMachine.loadAgentLibrary(agent)) even if the agent was loaded through the command-line option (-agentpath:/Absolute/Path/to/agentLibrary) at startup.

Here, you mean " when an agent is loaded dynamically with the -XX:+EnableDynamicAgentLoading option"?

What do you mean by "only issue one warning message which is not AIX-specific capability"?

If an agent is loaded dynamically with the same name or absolute path, OpenJ9 VM is able to compare it with previously loaded libraries and determine if it was already loaded, in case the agent library was loaded before, no more warnings are issued.
However, if the same library is loaded differently, for example, one with a platform-independent name such as VirtualMachine.loadAgentLibrary(agent), and the other with an absolute file path -agentpath:/Absolute/Path/to/agentLibrary, this use case requires the OS API to determine if the same library was loaded, AIX doesn't have such APIs like other platforms supported by OpenJ9, hence another warnings will be issued.

Sreekala-Gopakumar · 2023-09-21T16:05:36Z

Jenkins doc stage

Sreekala-Gopakumar · 2023-09-21T16:23:15Z

@JasonFengJ9 - I have incorporated the changes. Please check and confirm. Thanks!

JasonFengJ9

A few more minor comments, please incorporate them.

JasonFengJ9 · 2023-09-21T19:45:07Z

docs/xxenabledynamicagentloading.md

+
+You can disable the dynamic loading of the agents into a VM after startup with the `-XX:-EnableDynamicAgentLoading` option.
+
+![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java&trade; 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option. These warnings are not issued if the same agents were loaded before at startup either by using the [command-line options](interface_jvmti.md#overview) or an earlier dynamic loading.


Suggested change

![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java™ 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option. These warnings are not issued if the same agents were loaded before at startup either by using the [command-line options](interface_jvmti.md#overview) or an earlier dynamic loading.

![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java™ 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option. These warnings are not issued if the same agents were loaded before either by using the [command-line options](interface_jvmti.md#overview) at startup or an earlier dynamic loading.

Note: an agent dynamic loading always occurs after VM startup.

JasonFengJ9 · 2023-09-21T19:47:40Z

docs/xxenabledynamicagentloading.md

+
+These warnings are issued only once for the same agent when the `-XX:+EnableDynamicAgentLoading` option is not specified.
+
+If the `-XX:+EnableDynamicAgentLoading` option is set at startup, all agents that are dynamically loaded are considered as approved by the application owner, and therefore, no warnings are issued.


Also, note here that a command line option can only be specified at VM startup, not sure if "at startup" here is required.

JasonFengJ9 · 2023-09-21T19:52:03Z

docs/xxenabledynamicagentloading.md

+
+If the `-XX:+EnableDynamicAgentLoading` option is set at startup, all agents that are dynamically loaded are considered as approved by the application owner, and therefore, no warnings are issued.
+
+Eclipse OpenJ9&trade; supported operating systems other than AIX&reg; have APIs to determine whether the same agent was loaded before or not, even if an agent is loaded with the same or different name and absolute path.


Suggested change

Eclipse OpenJ9™ supported operating systems other than AIX® have APIs to determine whether the same agent was loaded before or not, even if an agent is loaded with the same or different name and absolute path.

Eclipse OpenJ9™ supported operating systems other than AIX® have APIs to determine whether the same agent was loaded before or not, even if an agent is loaded with a platform-independent name or an absolute path to the platform-dependent library.

JasonFengJ9 · 2023-09-21T19:54:41Z

docs/xxenabledynamicagentloading.md

+
+Eclipse OpenJ9&trade; supported operating systems other than AIX&reg; have APIs to determine whether the same agent was loaded before or not, even if an agent is loaded with the same or different name and absolute path.
+
+AIX systems cannot detect whether an agent was previously loaded or not if the agent was loaded through a different name or path. Therefore, on AIX systems, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the same agent was loaded before through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)


Suggested change

AIX systems cannot detect whether an agent was previously loaded or not if the agent was loaded through a different name or path. Therefore, on AIX systems, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the same agent was loaded before through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)

AIX systems cannot detect whether an agent was previously loaded or not if the agent was loaded through a platform-independent name or an absolute path to the platform-dependent library. Therefore, on AIX systems, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the same agent was loaded before through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)

eclipse-openj9#1140 Created a new topic for the -XX:[+|-]EnableDynamicAgentLoading option Updated the related topics. Incorporated the review feedback. Closes eclipse-openj9#1140 Signed-off-by: Sreekala Gopakumar <sreekala.gopakumar@ibm.com>

Sreekala-Gopakumar · 2023-09-22T10:45:28Z

Jenkins doc stage

JasonFengJ9

LGTM

Thanks @Sreekala-Gopakumar

Sreekala-Gopakumar · 2023-09-22T11:40:27Z

@JasonFengJ9 - I have updated the documents. Please check and confirm. Thanks!

Sreekala-Gopakumar · 2023-09-22T12:37:38Z

@pshipton - Jason has approved the changes. Can this be merged or are there any other changes that you might want me to make? Thanks!

@pshipton - Any feedback?

Sreekala-Gopakumar · 2023-09-22T15:20:32Z

Jenkins doc stage

JasonFengJ9 reviewed Sep 21, 2023

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Sreekala-Gopakumar force-pushed the 1140EnableDynLoad branch from 5824eb1 to 80bfe9a Compare September 21, 2023 16:01

JasonFengJ9 reviewed Sep 21, 2023

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Sreekala-Gopakumar force-pushed the 1140EnableDynLoad branch from 80bfe9a to b30629c Compare September 22, 2023 10:39

JasonFengJ9 approved these changes Sep 22, 2023

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pshipton approved these changes Sep 25, 2023

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pshipton merged commit 0a4b815 into eclipse-openj9:master Sep 25, 2023

Sreekala-Gopakumar deleted the 1140EnableDynLoad branch January 19, 2024 03:09

Sreekala-Gopakumar mentioned this pull request Feb 5, 2024

JDK21+ AIX prints a warning message for the same library previously loaded #1264

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Documentation for -XX:[+|-]EnableDynamicAgentLoading #1174

Documentation for -XX:[+|-]EnableDynamicAgentLoading #1174

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		@@ -0,0 +1,60 @@
		<!--
		* Copyright (c) 2017, 2023 IBM Corp. and others

	* Copyright (c) 2017, 2023 IBM Corp. and others
	* Copyright (c) 2023, 2023 IBM Corp. and others


		You can disable the dynamic loading of the agents into a VM after startup with the `-XX:-EnableDynamicAgentLoading` option.

		![Start of content that applies to Java 21 (LTS) and later](cr/java21plus.png) For Java™ 21 and later, the following warnings are issued when the agents are loaded dynamically into a running VM after startup without specifying the `-XX:+EnableDynamicAgentLoading` option and the same agents were not loaded at startup by using the [command-line options](interface_jvmti.md#overview):


		These warnings are issued only once for the same agent when the `-XX:+EnableDynamicAgentLoading` option is not specified.

		If the `-XX:+EnableDynamicAgentLoading` option is set at startup, all agents that are dynamically loaded are considered as approved by the application owner, and therefore, no warnings are issued.


		If the `-XX:+EnableDynamicAgentLoading` option is set at startup, all agents that are dynamically loaded are considered as approved by the application owner, and therefore, no warnings are issued.

		Eclipse OpenJ9™ supported operating systems other than AIX® have APIs to determine whether the same agent was loaded before or not, even if an agent is loaded with the same or different name and absolute path.


		Eclipse OpenJ9™ supported operating systems other than AIX® have APIs to determine whether the same agent was loaded before or not, even if an agent is loaded with the same or different name and absolute path.

		AIX systems cannot detect whether an agent was previously loaded or not if the agent was loaded through a different name or path. Therefore, on AIX systems, the warnings are issued when an agent is loaded dynamically through the Attach API (`VirtualMachine.loadAgentLibrary(agent)`) even if the same agent was loaded before through the command-line option (`-agentpath:/Absolute/Path/to/agentLibrary`) at startup. ![End of content that applies to Java 21 (LTS) and later](cr/java_close_lts.png)

Documentation for -XX:[+|-]EnableDynamicAgentLoading #1174

Documentation for -XX:[+|-]EnableDynamicAgentLoading #1174

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