RFR : 8215962: Support ThreadPriorityPolicy mode 1 for non-root users on linux/bsd

[Baesken, Matthias]

> I still want to know how the OS_ERR gets handled by all the higher level
> code. How will this failure at runtime get reported back to application  code?

Hi David ,   the "best practice"  currently is  to just ignore  the return code  of  os::set_native_priority  , it is called and we hope for the best  ,
 for example :

jdk/src/hotspot/share/runtime/vmThread.cpp

299  int prio = (VMThreadPriority == -1)
300    ? os::java_to_os_priority[NearMaxPriority]
301    : VMThreadPriority;
302  // Note that I cannot call os::set_priority because it expects Java
303  // priorities and I am *explicitly* using OS priorities so that it's
304  // possible to set the VM thread priority higher than any Java thread.
305  os::set_native_priority( this, prio );


jdk/src/hotspot/share/compiler/compileBroker.cpp

783      int native_prio = CompilerThreadPriority;
784      if (native_prio == -1) {
785        if (UseCriticalCompilerThreadPriority) {
786          native_prio = os::java_to_os_priority[CriticalPriority];
787        } else {
788          native_prio = os::java_to_os_priority[NearMaxPriority];
789        }
790      }
791      os::set_native_priority(thread, native_prio);


A difference is   

jdk/src/hotspot/share/runtime/os.cpp

217OSReturn os::set_priority(Thread* thread, ThreadPriority p) {
218  debug_only(Thread::check_for_dangling_thread_pointer(thread);)
219
220  if (p >= MinPriority && p <= MaxPriority) {
221    int priority = java_to_os_priority[p];
222    return set_native_priority(thread, priority);

Where the return  code  of  set_native_priority()   is returned   (however then it is later usually  not handled by the callers of os::set_priority.

>
> As I stated this is not a complete statement as on Linux at least you
> also have to account for RLIMIT_RTPRIO.
>

If you want me to do, I can for course add a short statement about this .


Best regards, Matthias


> -----Original Message-----
> From: David Holmes <david.holmes at oracle.com>
> Sent: Donnerstag, 3. Januar 2019 14:02
> To: Baesken, Matthias <matthias.baesken at sap.com>;
> daniel.daugherty at oracle.com; 'hotspot-dev at openjdk.java.net' <hotspot-
> dev at openjdk.java.net>
> Subject: Re: RFR : 8215962: Support ThreadPriorityPolicy mode 1 for non-root
> users on linux/bsd
> 
> Hi Matthias,
> 
> On 3/01/2019 9:13 pm, Baesken, Matthias wrote:
> > Hello David and Dan ,  here is a second webrev :
> >
> > http://cr.openjdk.java.net/~mbaesken/webrevs/8215962.1/
> >
> > - adjusted copyright years + fixed some typos
> > - added  the missing return for FreeBSD  (pointed out by  Dan)
> > - removed  the  warning message  completely
> 
> I still want to know how the OS_ERR gets handled by all the higher level
> code. How will this failure at runtime get reported back to application
> code?
> 
> ! // It is only used when ThreadPriorityPolicy=1 and requires root
> privilege or
> ! // CAP_SYS_NICE capability.
> 
> As I stated this is not a complete statement as on Linux at least you
> also have to account for RLIMIT_RTPRIO.
> 
> Thanks,
> David
> -----
>