RFR: 8328630: Add logging when needed symbols in dll are missing. [v2]

[Robbin Ehn]

On Thu, 21 Mar 2024 10:50:12 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> src/hotspot/os/posix/os_posix.cpp line 714:
>> 
>>> 712: 
>>> 713: void* os::dll_lookup(void* handle, const char* name) {
>>> 714:   ::dlerror(); // Clear any previous error
>> 
>> Uggghhh! It is awful that we need to do that. Now this needs to be guarded with `log_is_enabled(Debug, os)`. Otherwise we need to check for the performance hit of doing this, particularly during startup.
>
> The result are stored in per thread struct, so that method just load that thread local and check that result is NULL and returns. IMHO that's fine.
> 
> If there is an error it must free it, so maybe considering all the libjsvml ~40-50 errors that must be freed ?
> 
> Thinking about it, those 40-50 failed lookups are much, much, more expensive.
> So it would make more sense to fix that side.

Here is the data: Avg:187.913 ns Sum:40965 ns

Want me to add the guard? I don't mind.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18404#discussion_r1535364154