RFR: JDK-8320890: [AIX] Find a better way to mimic dl handle equality [v8]

[Thomas Stuefe]

On Thu, 21 Dec 2023 09:37:57 GMT, Joachim Kern <jkern at openjdk.org> wrote:

>> src/hotspot/os/aix/porting_aix.cpp line 916:
>> 
>>> 914: constexpr int max_handletable = 1024;
>>> 915: static int g_handletable_used = 0;
>>> 916: static struct handletableentry g_handletable[max_handletable] = {{0, 0, 0, 0}};
>> 
>> Wouldn't `ConcurrentHashTable` be a better data structure? It is already used in hotspot, can grow dynamically and doesn't need linear search.
>
> There will be only few libraries in the list. With this assumption Thomas suggested to use just a simple array.

Let's keep it simple. A linear array of only a few items is easily scanned, probably faster than pointer hopping hash table entries. Not that it matters in any way for the few calls to dlopen.

Also, avoiding hotspot structures preserves layer integrity (porting_aix does not pull anything from hotspot so far) and prevents initialisation time dependencies. Not sure whether ConcurrentHashTable works before VM init, but with Joachimes current solution, we can call dlopen at any time in VM life.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16920#discussion_r1433839119