RFR: 8317432: Async UL: Do not recompute strlen()

[Johan Sjölen]

On Wed, 4 Oct 2023 13:58:33 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Hi,
>> 
>> This change does three things:
>> 
>> 1. At construction of message we used to compute `strlen` and then `strcpy`, we change this to do only one `strlen` and then a `memcpy` instead.
>> 2. A `strlen` used to be required to calculate the size when finding the next message in the iterator. We instead store the previously computed message length and so the `strlen` is no longer necessary. The cost of this is 8 bytes extra per message (64 -> 72 bytes).
>> 3. There's also some code which alters the alignment to explicitly handle the alignment of `Message` and ensure that `_pos` starts at a `Message`-aligned pointer.
>
> src/hotspot/share/logging/logAsyncWriter.hpp line 87:
> 
>> 85:     LogFileStreamOutput* const _output;
>> 86:     const LogDecorations _decorations;
>> 87:     size_t _msglen; // Length of message excluding NUL-byte
> 
> Is it `const`?

Thanks, it is `const`. Same for the other comment.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16029#discussion_r1346039611