RFR: 8286180: Enable construction of LogStreamImpl from LogMessageImpl [v5]

[Johan Sjölén]

On Mon, 23 May 2022 07:00:48 GMT, David Holmes <dholmes at openjdk.org> wrote:

> The code looks reasonable just reading through the changes, but I'm missing something fundamental here. We have:
> 
> `class NonInterleavingLogStream : public LogStreamImpl<LogMessageHandle>`
> 
> and
> 
> `class LogStream : public LogStreamImpl<LogTargetHandle>`
> 
> but I can't tell what makes the former "non-inter-leaving" while the latter is "inter-leaving" , nor do I understand the test cases for these.
> 
> Thanks.

@dholmes-ora

`LogMessageHandle` and `LogTargetHandle` provides different guarantees. The former guarantees that all lines are logged without interleaving and the latter does not guarantee this. The former takes a bit more memory, so it's sometimes preferable to use the latter.

The tests `(Non)InterleavingStream` show that the output order differs between the two log streams. For the non-interleaving log stream the `log_info()` calls are all lumped together at the start, because the stream messages will be flushed together. This is not the case for the `InterleavingStream` test where the `log_info()` messages interleave with the stream messages.

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PR: https://git.openjdk.java.net/jdk/pull/8748