RFR: JDK-8277795: ldap connection timeout not honoured under contention

[Daniel Fuchs]

On Thu, 25 Nov 2021 23:54:18 GMT, Rob McKenna <robm at openjdk.org> wrote:

> This fix attemps to resolve an issue where threads can stack up on each other while waiting to get a connection from the ldap pool to an unreachable server. It does this by having each thread start a countdown prior to holding the pools' lock. (which has been changed to a ReentrantLock) Once the lock has been grabbed, the timeout is adjusted to take the waiting time into account and the process of getting a connection from the pool or creating a new one commences.
> 
> Note: this fix also changes the meaning of the connection pools initSize somewhat. In a situation where we have a large initSize and a small timeout the first thread could actually exhaust the timeout before creating all of its initial connections. Instead this fix simply creates a single connection per pool-connection-request. It continues to do so for subsequent requests regardless of whether an existing unused connection is available in the pool until initSize is exhausted. As such it may require a CSR.

What testing is there for this fix?

src/java.naming/share/classes/com/sun/jndi/ldap/LdapClientFactory.java line 71:

> 69:         throws NamingException {
> 70:         return new LdapClient(host, port, socketFactory,
> 71:                 (int)timeout, readTimeout, trace, pcb);

A blunt cast from `long` to `int` is a bit worrying as it could lead to positive values becoming negative, unless you have checks in place in the calling code that will ensure that the long value is never > Integer.MAX_VALUE? And it could also result in a large value becoming a small positive value.
I'd suggest to remove the inconsistency one way or the other - or add an explicit check to make it obvious that this case cannot happen.

src/java.naming/share/classes/com/sun/jndi/ldap/pool/Pool.java line 141:

> 139: 
> 140:         if (!conns.grabLock(remaining)) {
> 141:             throw new NamingException("Timed out waiting for lock");

Is this the appropriate exception? I see in `checkRemaining`:

                throw new CommunicationException(
                        "Timeout exceeded while waiting for a connection: " +
                                timeout + "ms");

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PR: https://git.openjdk.java.net/jdk/pull/6568