RFR: 8153133: Thread.dumpStack() can use StackWalker [v2]

[Jaikiran Pai]

On Mon, 8 Nov 2021 15:53:54 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>>> printStackTrace interacts with locking of the streams to avoid garbled output when many threads are printing to standard output output/error at the same time. If we change dumpStack to use StackWalker then it will need to do the same.
>> 
>> Indeed. I have updated the PR to use a lock while writing out to the `System.err`.
>> I had a look at the `printStackTrace()` implementation and it ends up locking the `PrintStream` (`System.err`) or `PrintWriter` for the duration of the entire stacktrace printing of each stacktrace element. The updated PR thus uses `System.err` as the lock to match that semantic.
>
>> The recursive initialisation issue will require discussion to see if we can avoid StackWalker.getInstance return null (which I assume is masking the issue).
> 
> For a better context, here's the stacktrace of such a call to `Thread.dumpStack` during the class initialization of `StackWalker`:
> 
> Caused by: java.lang.NullPointerException: Cannot invoke "java.lang.StackWalker.forEach(java.util.function.Consumer)" because the return value of "java.lang.StackWalker.getInstance()" is null
> 	at java.base/java.lang.Thread.dumpStack(Thread.java:1383)
> 	at java.base/java.security.AccessController.checkPermission(AccessController.java:1054)
> 	at java.base/java.lang.SecurityManager.checkPermission(SecurityManager.java:411)
> 	at java.base/java.lang.reflect.AccessibleObject.checkPermission(AccessibleObject.java:91)
> 	at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
> 	at java.base/java.lang.Class$3.run(Class.java:3864)
> 	at java.base/java.lang.Class$3.run(Class.java:3862)
> 	at java.base/java.security.AccessController.doPrivileged(AccessController.java:318)
> 	at java.base/java.lang.Class.getEnumConstantsShared(Class.java:3861)
> 	at java.base/java.lang.System$2.getEnumConstantsShared(System.java:2295)
> 	at java.base/java.util.EnumSet.getUniverse(EnumSet.java:408)
> 	at java.base/java.util.EnumSet.noneOf(EnumSet.java:111)
> 	at java.base/java.lang.StackWalker.<clinit>(StackWalker.java:291)
> 
> As you will notice, this call comes from the security (permission check) layer when `StackWalker` class is being `clinit`ed. The check for `StackWalker.getInstance()` being `null`, in the `Thread.dumpStack()` implementation is indeed almost a hackish way to identify this case where  `StackWalker`'s `clinit` is in progress (in the current thread). I can't think of a different way to handle this use case, so looking forward to any suggestions.

> The updated PR thus uses System.err as the lock to match that semantic.

The test case has also been updated to add a new test which invokes Thread.dumpStack() from multiple threads and verifies that the stacktrace written out isn't garbled. Running the test _without_ the addition of the lock on System.err in the Thread.dumpStack implementation does indeed show the garbled output and causes the test failure (which is a good thing).

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PR: https://git.openjdk.java.net/jdk/pull/6292