On Mon, 12 Aug 2024 17:07:42 GMT, Doug Lea <d...@openjdk.org> wrote: > The Exchanger class uses spin-waits that are hostile to some uses of > VirtualThreads. Improving this requires a means of estimating whether there > are many VirtualThreads with few carriers, which can be supported by adding a > method in class ForkJoinWorkerThread. This enables a reworking of the > exchange method, and can also be used to deal with similar issues in > LinkedTransferQueue and possibly elsewhere. We leave for now open whether > this method (hasKnownQueuedWork) should be public, which would allow users to > use it in similar contexts, at the possible expense of revealing too much > about current VT implementation
I had forgotten that there was already a stripped-down jtreg version of an Exchanger test in test/jdk/java/util/concurrent/Exchanger. So I updated it to include virtual, platform and mixes. (Also including enough iterations and stages to reduce noisiness. Here's a sample run: Warmup... Threads: 2 PLATFORM : 195 ns per transfer Threads: 3 PLATFORM : 226 ns per transfer Threads: 4 PLATFORM : 172 ns per transfer Threads: 5 PLATFORM : 148 ns per transfer Threads: 6 PLATFORM : 123 ns per transfer Threads: 7 PLATFORM : 100 ns per transfer Threads: 8 PLATFORM : 96 ns per transfer Threads: 9 PLATFORM : 78 ns per transfer Threads: 2 VIRTUAL : 185 ns per transfer Threads: 3 VIRTUAL : 223 ns per transfer Threads: 4 VIRTUAL : 194 ns per transfer Threads: 5 VIRTUAL : 139 ns per transfer Threads: 6 VIRTUAL : 121 ns per transfer Threads: 7 VIRTUAL : 118 ns per transfer Threads: 8 VIRTUAL : 190 ns per transfer Threads: 9 VIRTUAL : 79 ns per transfer Threads: 2 MIXED : 161 ns per transfer Threads: 3 MIXED : 196 ns per transfer Threads: 4 MIXED : 164 ns per transfer Threads: 5 MIXED : 146 ns per transfer Threads: 6 MIXED : 123 ns per transfer Threads: 7 MIXED : 106 ns per transfer Threads: 8 MIXED : 102 ns per transfer Threads: 9 MIXED : 87 ns per transfer ------------- PR Comment: https://git.openjdk.org/jdk/pull/20554#issuecomment-2302143653
