RFR: 8289919: [test] LoadLibraryUnloadTest.java failed with "Failed to unload native library" [v2]

[Mandy Chung]

On Wed, 13 Jul 2022 14:06:00 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> The test `java/lang/ClassLoader/loadLibraryUnload/LoadLibraryUnloadTest.java`
>> Fails intermittently when expected output from a subprocess is not found.
>> 
>> I suspect a race between the Cleaner that is going to call JNI_OnUnload (in NativeLibraries.java:377) when the ClassLoader is no longer referenced and the test code that exits as soon as it detects that the p.Class1 is no longer referenced.
>> 
>> The proposed fix is to create a canary object referenced by the native library and released when the library is unloaded.
>> The Java side of the test provides the canary object and uses a WeakReference to wait for it to be released.
>> When released the child process exits and the driver test will find all of the output it expects.
>
> Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleanup waiting for library unload

Looks good.  The solution is a good way to fix this race.   Thanks for fixing this.

test/jdk/java/lang/ClassLoader/loadLibraryUnload/LoadLibraryUnload.java line 168:

> 166:         for (int i = 0; i < LOADER_COUNT; i++) {
> 167:             System.gc();
> 168:             var res = refQueue.remove();

This should block until one becomes available or `InterruptedException` gets thrown.   So `res` would never be null?

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Marked as reviewed by mchung (Reviewer).

PR: https://git.openjdk.org/jdk/pull/9474