RFR(S): 8186293: [aix] Fix thread creation with huge stack sizes

[David Holmes]

Hi Thomas,

On 17/08/2017 5:07 PM, Thomas Stüfe wrote:
> 
> On Thu, Aug 17, 2017 at 8:52 AM, Lindenmaier, Goetz 
> <goetz.lindenmaier at sap.com <mailto:goetz.lindenmaier at sap.com>> wrote:
> 
>     Hi David,
> 
>     > I wonder whether a fatal error "Error occurred during initialization of
>     > VM" would not be better than just logging a warning?
>     I skip thread creation if the error code is != 0 and return false as it
>     happens on linux. So you see the exact same behavior. Only I
>     print the additional message about the stack size because that
>     is missing from the pthread attr which is reported (as setting it
>     failed).
> 
> 
> Platforms seem to have different behaviour now:
> 
> AIX debug (with your patch): if either one of 
> pthread_attr_setstacksize(), pthread_attr_setguardsize or pthread_create 
> fails, we log a warning and return an error.
> AIX release: ditto.
> 
> Linux debug: if pthread_attr_setstacksize fails, we assert. We ignore 
> errors from pthread_attr_setguardsize. If pthread_create fails, we log a 
> warning and return an error.
> Linux release: We ignore errors from both pthread_attr_setstacksize and 
> pthread_attr_setguardsize. If pthread_create fails, we log a warning and 
> return an error.

To me the asserts are there to catch basic usage errors that indicate a 
general programming bug (eg something uninitialized). They will also 
catch an "illegal argument" if the API detects that, but that is secondary.

If pthread_create fails we do as you say, but if this is a system 
problem (like bad -Xss) then it will fail the first JavaThread  creation 
and we will get the "Error occurred during initialization".

> I think it would be nice to have consistent behavior for all platforms. 

Yes consistency would be nice but if one platform has more error 
checking then another then we'd have to drop assertions, even if we 
don't ever expect a failure on that platform.

> Not sure if this needs to be done with this patch here. As for an "Error 
> occurred during initialization" (debug only or release too?) - can we be 
> sure this only happens at initialization? Could it not be possible for 
> java threads with different stack sizes to be started later, and 
> triggering the same error?

I would expect a large stacksize passed to j.l.Thread constructor to 
also be able to trigger this. But bad -Xss/-XX:ThreadStackSize will 
cause initialization to fail.

> I think I prefer to always have a runtime error (both in debug and 
> release builds), as Goetz did in his current AIX patch. And maybe have a 
> sensible Exception text.

If pthread_create fails we have no detail as to exactly why. If 
pthread_attr_setstacksize does then we have a reasonable idea. So not 
sure what you would suggest.

But in any case, as you suggest, this would all be a separate 
enhancement request.

Cheers,
David

> Kind Regards, Thomas
> 
> 
>     I removed the reference to linux, although I find it useful to
>     point out such unexpected differences.
>     http://cr.openjdk.java.net/~goetz/wr17/8186293-aixHugeStack/webrev.02/
>     <http://cr.openjdk.java.net/~goetz/wr17/8186293-aixHugeStack/webrev.02/>
> 
>     Best regards,
>        Goetz.
> 
> 
> 
> 
>      > -----Original Message-----
>      > From: David Holmes [mailto:david.holmes at oracle.com
>     <mailto:david.holmes at oracle.com>]
>      > Sent: Wednesday, August 16, 2017 10:54 PM
>      > To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com
>     <mailto:goetz.lindenmaier at sap.com>>; hotspot-runtime-
>      > dev at openjdk.java.net <mailto:dev at openjdk.java.net>
>      > Subject: Re: RFR(S): 8186293: [aix] Fix thread creation with huge
>     stack sizes
>      >
>      > On 17/08/2017 12:24 AM, Lindenmaier, Goetz wrote:
>      > > Hi,
>      > >
>      > > TestOptionWithRanges causes the vm on aix to crash on some
>     machines.
>      > > This is because huge stack sizes are not treated properly.
>      > >
>      > > On linux, pthread_attr_setstacksize succeeds if called with
>     huge values, but
>      > > pthread_create() then fails. On Aix, pthread_attr_setstacksize 
>     fails if
>      > > passed a value exceeding the limits and leaves the minimal system
>      >
>      > The AIX behaviour is more in spirit with POSIX.
>      >
>      > > thread stack size in attr. Thus thread creation succeeds and
>     leads to
>      > > crashes after thread creation when the guard pages shall be
>     protected
>      > > but don't fit on the tiny stack created.
>      > >
>      > > Please review this small, aix-only change.
>      > > http://cr.openjdk.java.net/~goetz/wr17/8186293-
>     <http://cr.openjdk.java.net/~goetz/wr17/8186293->
>      > aixHugeStack/webrev.01/
>      >
>      > I wonder whether a fatal error "Error occurred during
>     initialization of
>      > VM" would not be better than just logging a warning?
>      >
>      > As Thomas notes, no need to discuss/describe what may or may not
>     happen
>      > on other platforms.
>      >
>      > Cheers,
>      > David
>      >
>      > > Best regards,
>      > >    Goetz.
>      > >
> 
>