RFR: 8293562: blocked threads with KeepAliveCache.get [v4]

[Michael McMahon]

On Wed, 28 Sep 2022 15:36:04 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 two additional commits since the last revision:
> 
>  - Close connections in finally block
>  - Fix copyright year

src/java.base/share/classes/sun/net/www/http/KeepAliveCache.java line 125:

> 123:     @SuppressWarnings("removal")
> 124:     public void put(final URL url, Object obj, HttpClient http) {
> 125:         HttpClient oldClient = null;

Could you put a comment in there explaining what oldClient is exactly? Eg that it is a client that ends up being closed, either from the cache to make way for the newest entry or if the current client needs to be closed.

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