Hi Patrick,
First apologies that it took me so long to get my head around this. :)
Let me summarise the problem as I see it.
The launcher specifies no particular semantics for -Xss0, to it 0 is
just a very small size. However the VM maps -Xss to -XX:ThreadStackSize
and for it 0 means "use the platform default stack size".
The launcher examines -Xss because it needs to use it to define the
stacksize for the initial thread created to launch the VM.
The VM examines -Xss to see what stacksize to use for subsequently
created threads and it treats 0 as 'use the platform default' and it
otherwise checks the value against some hardcoded minimums and reports
an error if it is too small.
The initial thread that loads the VM needs sufficient stack to be able
to process things to the point where it can determine that the requested
stacksize is too small and report the error. The value of the minimum
stack is hardcoded into the launcher, as STACK_SIZE_MINIMUM (64KB). If
the -Xss value is less than that then it gets set to that.
If no -Xss is specified then the launcher asks the VM for a reasonable
value to use for the stacksize of the initial thread (typically 1MB).
The problem arises with -Xss0 because this causes the launcher to set an
initial thread stacksize of STACK_SIZE_MINIMUM, but the VM sees this as
"use the default" and so does not reject it and tries to continue with
VM initialization. That can't succeed as we only have a tiny
STACK_SIZE_MINIMUM stack and so we get StackOverflowError (or fail an
assert in debug builds).
So the solution, as Patrick proposes, is to treat -Xss0 in the launcher
as-if -Xss has not been set and so use the VM suggested default for the
initial thread's stacksize.
So I agree with the functional change here, but have some alternate
suggestions for additional commentary. Unfortunately I have to step away
at the moment (its Friday night) so will send that later - sorry.
Thanks,
David
On 12/04/2019 5:51 pm, Patrick Zhang OS wrote:
Moved this to core-libs-dev for review, thanks.
Dropped and bcc'ed jdk-dev and jdk-updates-dev.
Regards
Patrick
-----Original Message-----
From: David Holmes <david.hol...@oracle.com>
Sent: Friday, April 12, 2019 3:43 PM
To: Patrick Zhang OS <patr...@os.amperecomputing.com>; jdk-...@openjdk.java.net
Cc: jdk-updates-...@openjdk.java.net
Subject: Re: RFR: 8222334: java -Xss0 triggers StackOverflowError
Hi Patrick,
Please takes this to core-libs-dev for review.
Thanks,
David
On 12/04/2019 5:24 pm, Patrick Zhang OS wrote:
Hi,
Please review this patch.
The problem is that the launcher does a check on the input -Xss and
ensure it >=64K for the initial thread, while vm has another function
to determine whether the input stack size is big enough to future
threads, such as cgc_thread, vm_thread, java_thead etc. However if
-Xss0, the initial thread is created with stack size 64K, while others
use hotspot/system default sizes, which would trigger
StackOverflowError. We could either fine tune the threshold 64K to be
a bigger one, or have the initial thread created with system defaults
that may be what the user expects. This patch chooses the second
solution, to avoid potential side-effect of the first.
This can be reproduced with 10, 11, 12 too, so I cc'ed jdk-updates-dev here.
More details please refer to the ticket.
JBS: https://bugs.openjdk.java.net/browse/JDK-8222334
Webrev: http://cr.openjdk.java.net/~qpzhang/8222334/webrev.01/
Thanks for David's comments in Jira.
Regards
Patrick
