RFR(s): 8235410: Enable handshakes on Linux x86 (32-bit)

[Daniel D. Daugherty]

Thumbs up.

One left after this:

 > src/hotspot/cpu/arm/globals_arm.hpp:define_pd_global(bool, 
ThreadLocalHandshakes, false);

but that one should be take care of with the fix for:

8229971 Arm32: implementation for Thread-local handshakes

that Boris sent out for review...

Almost there...

Dan


On 12/5/19 9:01 AM, Robbin Ehn wrote:
> Hi all, please review.
>
> The flag ThreadLocalHandshakes is going to be obsolete in JDK 14.
> So we change the (unchangeable) default for Linux x86 to on/true.
>
> There is a follow-up which removes ThreadLocalHandshakes completely.
> If the platform defines THREAD_LOCAL_POLL it will use handshakes.
> When arm32 have implemented local polls, the plan is to remove the 
> global poll
> code paths.
>
> Last time I checked with some of the affected parties there was no 
> objections.
>
> Built and sanity test.
>
> Issue:
> https://bugs.openjdk.java.net/browse/JDK-8235410
>
> Code below.
>
> Thanks, Robbin
>
> diff -r 636d71e53732 src/hotspot/cpu/x86/globals_x86.hpp
> --- a/src/hotspot/cpu/x86/globals_x86.hpp    Wed Dec 04 10:26:32 2019 
> +0100
> +++ b/src/hotspot/cpu/x86/globals_x86.hpp    Thu Dec 05 14:13:57 2019 
> +0100
> @@ -89,12 +89,7 @@
>
>  define_pd_global(intx, InitArrayShortSize, 8*BytesPerLong);
>
> -#if defined(_LP64) || defined(_WINDOWS)
>  define_pd_global(bool, ThreadLocalHandshakes, true);
> -#else
> -// get_thread() is slow on linux 32 bit, therefore off by default
> -define_pd_global(bool, ThreadLocalHandshakes, false);
> -#endif
>
>  #define ARCH_FLAGS(develop, \
>                     product, \
>