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

Chris Plummer chris.plummer at oracle.com
Thu Mar 16 05:03:11 UTC 2017

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

More information about the hotspot-dev mailing list