On Wed, 5 May 2021 08:11:04 GMT, Robbin Ehn <r...@openjdk.org> wrote:
> Please consider this change which removes the manual transitions to blocked. > This adds a preprocess template/functor which is executed in the destructor > of 'ThreadBlockInVM' if we are going to do any processing. > This gives us a way to backout of the object/raw monitor before suspend or > other processing, such as a safepoint. > > The object monitor code could be straight forward changed to use this instead > of manual transitions. > > Raw monitors on the other hand are a bit more complicated due to 'implicit' > rules (consequences of the specs). > Added a comment in hpp trying to explain it; we cannot simply transition with > a raw monitor held. > This caused the change in the destructor ~ThreadInVMfromNative() (this > specific change have also been tested in unrelated exploration of > transition), now this RAII does the same as we do when going to native from > Java, just setting the state. > Since we are going from an unsafe state, in VM, to a safe state, in native, > we do not need to check the poll. > That made it possible to careful use ThreadInVMfromNative in raw monitors. > > I also remove the early CAS in raw_enter. > We lock a lock to do a CAS, in the uncontended case means CAS on lock then > CAS raw monitor. > Now we instead do a transitions, in the uncontended case means fence, CAS raw > monitor, fence. > (multiple fence (CAS is also a fence) very close to each other have little > additional performance impact on contemporary hardware) > > Passes t1-t7 and manual stressing relevant test groups. This pull request has now been integrated. Changeset: 97ec5ad0 Author: Robbin Ehn <r...@openjdk.org> URL: https://git.openjdk.java.net/jdk/commit/97ec5ad0a6ed2cd87a9c75b0559e9bb55b72121e Stats: 340 lines in 8 files changed: 119 ins; 150 del; 71 mod 8265753: Remove manual JavaThread transitions to blocked Reviewed-by: dcubed, rrich, dholmes, pchilanomate ------------- PR: https://git.openjdk.java.net/jdk/pull/3875
