(RFR)(S)(10): 8176768: hotspot ignores PTHREAD_STACK_MIN when creating new threads

[David Holmes]

On 17/03/2017 2:27 PM, Chris Plummer wrote:
> Ok, time for a new webrev:
>
> http://cr.openjdk.java.net/~cjplummer/8176768/webrev.01/webrev.hotspot

Looks good. Full agreement from me on all the below.

Thanks,
David

> The only thing that has changed since the first webrev are the asserts
> added to os_linux.cpp and os_bsd.cpp. And to summarize what we discuss
> already:
>
>  - The assert should never happen due to the stack size being too small
> since it will be at least PTHREAD_STACK_MIN.
>  - The assert should never happen due to an unaligned stack size because
> we always align it to the page size.
>  - Any assert would therefore be a VM bug and not due to user error.
>  - No fixing the java launcher. If the user specifies a stack that is
> too small, hotspot will already detect this. If the user specifies a
> stack size that is large enough but not page aligned, then we just
> ignore any error (if the platform doth protest) and the user gets a main
> thread with a stack size set to whatever the OS default is.
>
> I still need to retest (I only ran TooSmallStackSize.java), but figure
> getting agreement on the changes first would be best before I bog down
> our testing resources.
>
> thanks,
>
> Chris
>
> On 3/15/17 10:03 PM, Chris Plummer wrote:
>> Hello,
>>
>> Please review the following:
>>
>> https://bugs.openjdk.java.net/browse/JDK-8176768
>> http://cr.openjdk.java.net/~cjplummer/8176768/webrev.00/webrev.hotspot
>>
>> While working on 8175342 I noticed our stack size on xgene was 8mb
>> even though I was specifying -Xss72k. It turns out the following code
>> was failing:
>>
>>       pthread_attr_setstacksize(&attr, stack_size);
>>
>> Although we computed a minimum stack size of 72k, so -Xss72k should be
>> fine, pthreads on this platform requires the stack be at least 128k,
>> so it failed the pthread_attr_setstacksize() call. The end result is
>> pthread_attr_setstacksize() had no impact on the thread's stack size,
>> and we ended up with the platform default of 8mb. The fix is to round
>> up the following variables to PTHREAD_STACK_MIN after computing their
>> new values:
>>
>>       _java_thread_min_stack_allowed
>>       _compiler_thread_min_stack_allowed
>>       _vm_internal_thread_min_stack_allowed
>>
>> For solaris, there was an issue using PTHREAD_STACK_MIN. You need to
>> #define _POSIX_C_SOURCE >= 199506L in order to get PTHREAD_STACK_MIN
>> #defined, and this needs to be done before including OS header files.
>> I noticed that on solaris we were using thr_min_stack() elsewhere
>> instead of PTHREAD_STACK_MIN, so I decided to do the same with this
>> fix. Either way is ugly (the #define or using thr_min_stack()).
>>
>> And speaking of the existing use of thr_min_stack(), I deleted it. It
>> was being applied before any adjustments to the stack sizes had been
>> made (rounding and adding red, yellow, and shadow zones). This mean
>> the stack ended up being larger than necessary. With the above fix in
>> place, we are now applying thr_min_stack() after recomputing the
>> minimum stack sizes. If for any reason one of those stack sizes is now
>> too small, the correct fix is to adjust the initial stack sizes, not
>> apply thr_min_stack() to the initial stack sizes. However, it looks
>> like no adjustment is needed. I did something close to our nightly
>> testing on all affect platforms, and no new problems turned up.
>>
>> thanks,
>>
>> Chris
>
>