For me, the issue occurred only when I ran in Docker, and when I used a java command line agent like the DataDog APM agent (-javaagent:/dd-java-agent.jar). When I ran in my JDK11 runtime environment (without the agent) I did not get the warnings.

I had this issue after installing Java12 when trying to use the debugger with Intellij Idea. The solution that I found was to go into Setting and searching for async and unchecking the Instrumenting agent box.

I had this issue too after installing jdk-12.0.1_windows-x64_bin.zip when trying to use the debugger with IntelliJ IDEA. I was getting an error of (Java HotSpot(TM) 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended). I found, too, going into Setting and search for async and unchecking the Instrumenting agent box. Worked for me!

You can ignore this warning. It just means that class data sharing is disabled for classes not loaded by the bootstrap class loader.

From Improve Launch Times […] With Application Class-Data Sharing:

The JVM loads some of the JDK classes with the bootstrap class loader and the rest with the system class loader, but includes all of them in its default archive. When IntelliJ executes your project, it tells the JVM to load some code with the bootstrap class loader by appending to that class path (second part of the message). Now, that means that the portion of the archive that contains classes loaded by the system class loader is potentially invalidated and so the JVM partially deactivates sharing (first part of the message).

You could disable class data sharing completely with -Xshare:off, but you would lose some performance.

Java version must be 9 or higher.

For Intellij IDE -> Settings/Preferences dialog ( Ctrl+Alt+S ), go to Build | Execution | Deployment | Debugger | Async -> uncheck instrumenting agent

Today I found the same question as you. Situation: debug while set no breakpoint Solution: set at least one breakpoint before you click debug button!

If it is not critical you can change your jdk version. I've changed from jdk14 to jdk 11. Hope it will work for you.

1.Open the Preferences option;

2.Find the Build,Execution,Deployment option;

3.Enter the Debugger --> Async Stack Traces ;

4.Uncheck the Instrumenting agent(requires debugger restart) ;

Please see this for detailed information.

You have to put the red dots at the left side of the code line you will make debug . if not you get this massage on IntelliJ

Got same problem, and tried to solve it as was written above.

But then i got another solution of problem without changing settings.

Press mouse right button on your file where you put break point and want to debug. Then choose "Debug ur file name.method()".

Don't use debug button from tools window. Seems the problem is that Idea can't understand which file u want to debug.

That worked for me without changing async settings.

Screenshot

Got the same problem, and tried to solve it as was written all the above methods.

But still, I wasn't able to debug my file the only reason is that before debugging your program you need to set debug point that till which point we want to debug. So just click on the place shown in the figure and set debug point then our program will debug easily. without doing anything else. enter image description here