RFR: 8285398: Cache the results of constraint checks

[Daniel Jeliński]

On Fri, 22 Apr 2022 02:13:14 GMT, David Schlosnagle <duke at openjdk.java.net> wrote:

>> Profiling the TLS handshakes using SSLHandshake benchmark shows that a large portion of time is spent in HandshakeContext initialization, specifically in DisabledAlgorithmConstraints class.
>> 
>> There are only a few instances of that class, and they are immutable. Caching the results should be a low-risk operation.
>> 
>> The cache is implemented as a softly reachable ConcurrentHashMap; this way it can be removed from memory after a period of inactivity. Under normal circumstances the cache holds no more than 100 algorithms.
>
> src/java.base/share/classes/sun/security/util/DisabledAlgorithmConstraints.java line 969:
> 
>> 967:         result = checkAlgorithm(disabledAlgorithms, algorithm, decomposer);
>> 968:         cache.put(algorithm, result);
>> 969:         return result;
> 
> Would it be worth using `cache.computeIfAbsent` or do you want to avoid lambda allocation overhead and potentially blocking concurrent handshakes on writer thread?
> 
> Suggestion:
> 
>         return cache.computeIfAbsent(algorithm, algo -> checkAlgorithm(disabledAlgorithms, algo, decomposer));

I generally prefer using `get` over `computeIfAbsent` when optimizing for performance. While `computeIfAbsent` is more concise, it's also much slower than `get` when the entry is already present.

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PR: https://git.openjdk.java.net/jdk/pull/8349