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

[David Holmes]

On 16/03/2017 3:51 PM, Chris Plummer wrote:
> On 3/15/17 10:23 PM, David Holmes wrote:
>> Hi Chris,
>>
>> On 16/03/2017 3:03 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
>>
>> Change looks good.
>>
>>> 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);
>>
>> So these really should be checking return values, at least in debug
>> builds. But we can leave that until we refactor the thread startup
>> code into os_posix.cpp.
> I considered adding checks. I wasn't sure if we should abort or just
> print a warning if it failed.

When we check pthread lib routines we use:

    int status = pthread_mutex_lock(_mutex);
    assert_status(status == 0, status, "mutex_lock");

This is for things that should only fail if we have a programming error.

> What refactoring is planned?

"Planned" might be a bit strong :) I was thinking of a number of 
os_posix related cleanups for which issues exist, but also forgot that 
some of our general clean-up RFE's have been closed as WNF :( I may do 
some of them after hours anyway :)

David
-----

> Chris
>>
>> Thanks,
>> David
>> -----
>>
>>> 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
>
>