On Mon, 8 Nov 2021 15:46:22 GMT, Jaikiran Pai <[email protected]> wrote:
>> src/java.base/share/classes/java/lang/Thread.java line 1396:
>>
>>> 1394: // at this point in time. So we fallback to creating a
>>> Exception instance
>>> 1395: // and printing its stacktrace
>>> 1396: new Exception(Thread.currentThread().name + " Stack
>>> trace").printStackTrace();
>>
>> The recursive initialisation issue will require discussion to see if we can
>> avoid StackWalker.getInstance return null (which I assume is masking the
>> issue).
>>
>> 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.
>
>> 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.
-------------
PR: https://git.openjdk.java.net/jdk/pull/6292
