RFR: 8293562: blocked threads with KeepAliveCache.get [v5]

[Michael McMahon]

On Wed, 28 Sep 2022 17:31:46 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

>> Please review this patch that makes sure KeepAliveCache does not block all threads while closing sockets.
>> 
>> Changes:
>> - get operation no longer closes sockets; if there's no socket that is recent enough, get returns null and lets the cleaner thread close the sockets
>> - put operation closes sockets without holding the cache lock. Additionally, if the cache is full, it places the new connection in the cache and removes the oldest connection.
>> - the cleaner thread creates a list of connections to close, and then closes them after releasing the cache lock
>> - additionally, we set the socket timeout to 1 millisecond before calling socket.close
>> 
>> The new test fails with `Wait for second request timed out` without this patch, passes after the changes. Tiers 1-3 clean.
>
> Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Describe oldClient

src/java.base/share/classes/sun/net/www/http/KeepAliveCache.java line 330:

> 328:             long currentTime = System.currentTimeMillis();
> 329:             KeepAliveEntry e = peekFirst();
> 330:             if ((currentTime - e.idleStartTime) > nap) {

Since `peekFirst` can return null in theory, should we check for it? Currently `pop` is used which throws an exception instead, and probably means it doesn't happen in practice, but maybe it could be flagged in static source code analysis?

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PR: https://git.openjdk.org/jdk/pull/10401