[jdk17] RFR: 8267952: async logging supports to dynamically change tags and decorators

[Xin Liu]

On Thu, 24 Jun 2021 00:06:13 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> This patch fixed intermittent crashes of gtest/AsyncLogGtest.java. The root cause 
>> is that previous flush() can't guarantee flush all pending messages in AsyncLog
>> buffer. This patch implements flush() using a synchronizaton token and waits for
>> completion. This approach isn't MT-safe but it can serialize all flush() calls in
>> a thread. 
>> 
>> Two concurrent tests are appended to cover the hazard cases.
>> This patch also comments LogConfiguration::configure_output() MT-safety.
>
> src/hotspot/share/logging/logAsyncWriter.cpp line 196:
> 
>> 194:       AsyncLogMessage token(nullptr, d, nullptr);
>> 195: 
>> 196:       // not disposable
> 
> I don't know what "not disposable" means.

The reason I don't call enqueue_locked() here because it may be dropped due to buffer size. 
This is a control token. if it gets dropped, flush() will get stuck forever. 

not droppable?

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PR: https://git.openjdk.java.net/jdk17/pull/130