RFR: 8260306: Do not include osThread.hpp in thread.hpp

[Lois Foltan]

On Fri, 22 Jan 2021 18:02:10 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> thread.hpp is a popular header file (included by 856 out of 1000 HotSpot.o file), so we should try to minimize what files are included by thread.hpp.
> 
> We can replace the inclusion of osThread.hpp with a forward declaration of the OSThread class.
> 
> This reduces the number of .o files that include osThread.hpp to 42.
> 
> Tested with mach5: tier1, builds-tier2, builds-tier3, builds-tier4 and builds-tier5. Also locally: aarch64, arm, ppc64, s390, x86, and zero.

Looks good.
Lois

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Marked as reviewed by lfoltan (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2198