On Mon, 22 Feb 2021 13:03:04 GMT, Pavel Rappo <pra...@openjdk.org> wrote:
>> The standard doclet works by creating `HtmlDocument` objects and then >> writing them out. Writing them can be safely done on a separate thread, and >> doing so results in about an 8% speedup, by overlapping the write/IO time >> with the time to generate the next page to be written. >> >> The overall impact on the codebase is deliberately small, coming down to a >> critical `if` statement in `HtmlDocletWriter` to "write now" or "write >> later". As such, it is easy to disable the feature if necessary, although no >> issues have been found in practice. The background writer uses an >> `ExecutorService`, which provides a lot of flexibility, but experiments show >> that it is sufficient to use a single background thread and to block if new >> tasks come available while writing a file. >> >> The feature is "default on", with a hidden option to disable it if necessary. > > This change is on the right track. > > 1. Although I'm not sure how "utilization" translates to a similar > measurement obtained through a profiling tool, I do think we can use > "utilization" as a rough estimate. > > FWIW, on my machine the base "utilization" for JDK codebase is 13%. After I > have moved the initialization of the `start` timestamp from the creation of > the writer closer to the submission of the first task, "utilization" > increased to 17%. > > I'd recommend computing elapsed times using `java.lang.System.nanoTime`. > Using `nanoTime` avoids some hazards of using `currentTimeMillis` for such > purposes. > > 2. The `--background-writer` option is processed **after** the writer has > been created. To see the "utilization" numbers I had to tweak the change and > rebuild the project. To add to my earlier comment https://github.com/openjdk/jdk/pull/2665#discussion_r580185985. I reread the `ExecutorService` API to refresh my memory. It looks like there is **NO** happens-before edge between "actions taken by a task" and "awaitTermination returned true" . So, to read that `taskBusy` value safely we have to do something else. ------------- PR: https://git.openjdk.java.net/jdk/pull/2665
