Reject operations in such a case with LDAP_BUSY. If read_event feature
is on, just stop reading from the connection. However this could still
result in deadlocks in reasonable situations. Need to figure out better
ways to make it safe and still protect ourselves.

Switched off unless thread debugging is on, but still useful for static
analysis.

Similar to the algorithm presented in
https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-579.pdf

Not completely lock-free at the moment. Also the problems with epoch
based memory reclamation are still present - a thread actively observing
an epoch getting stuck will prevent LloadConnections and LloadOperations
being freed, potentially running out of memory.

Reuse the connection walking facility in timeout management.

Unregistration is a hack and we shoould either make the subsystems into
an entry (if monitor allows subentry generation) or implement subsystem
unregistration in back-monitor.

Ondřej Kuzník authored Dec 13, 2017 and Ondřej Kuzník committed Nov 17, 2020

Introduces pinned operations. When SASL bind finishes, we might still
have to maintain a link between the client an an upstream for future
bind operations if we got a SASL Bind in Progress result code. We zero
out the msgids and remember a server-unique identifer on the client and
the relevant operation that lets us retrieve that link again. This
operation is reclaimed just like anything else when connections drop.

Hopefully, this should work for LDAP TXN and VC Exop support with SASL
later as well since it allows for many-to-many links to exist.

Ondřej Kuzník authored Nov 22, 2017 and Ondřej Kuzník committed Nov 17, 2020

In preparation for operation timeout events.

Ondřej Kuzník authored Sep 25, 2017 and Ondřej Kuzník committed Nov 17, 2020

At the moment, no exops are processed internally, all are passed on
unchanged.