RFR: 8267952: async logging supports to dynamically change tags and decorators

[David Holmes]

On Tue, 8 Jun 2021 03:10:56 GMT, Xin Liu <xliu at openjdk.org> wrote:

> Support dynamic reconfiguration for async logging. 2 unittests are provided.
> The regression test discovers a race condition in LogTagSet::log() even with
> synchronous logging. It's not MT-safe if context switch happens between the
> creation of LogDecorations  and LogOutputList::Iterator. fixed.

src/hotspot/share/logging/logConfiguration.cpp line 268:

> 266:   //
> 267:   // LogDecorator is a set of decorators represented in a uint. sizeof(uint) is not greater than a machine word,
> 268:   // so store of it is atomic on the mainstream processors. I.e. readers see either its older value or new value.

This is not necessarily true - the field also has to have correct alignment to ensure atomic accesses. The convention we are adopting is that all racily accessed fields like _decorators should be declared volatile, and accessed using Atomic::load and Atomic::store.

-------------

PR: https://git.openjdk.java.net/jdk/pull/4408