This is accomplished by locking the entire database, and keeping it locked
until the last reference is unlocked. We get rid of per-reference locks,
because those are what cause race conditions.
Note that Db has the potential to deadlock when caching is being used,
and when caching isn't being used, an inconsistent state can occur. Future
changes to Db will fix both of these issues.
Apparently it can EAGAIN on non-blocking connections... I don't think
LibreSSL's TLS library does this, but something to keep in mind if it
doesn't work for somebody.
tls_read() and tls_write() may return TLS_WANT_POLLIN or TLS_WANT_POLLOUT
if data isn't ready to be read or written yet. We have to account for this
by converting it to EAGAIN, which is how a typical read() or write()
function should behave.
Also installed a SIGPIPE handler; we do not want to be terminated by
SIGPIPE, and it's safe to ignore this signal because it should be
handled thoroughly in the code.
This is useful for having a TLS and a non-TLS version port, like Synapse.
I verified that the multiple-servers does in fact work as intended,
although the TLS server part is broken; I must be doing something
incorrectly with LibreSSL in setting up the server.
This way, we can still set the debug level in the configuration, and not
see the log just absolutely flooded with memory allocations and whatnot.
This is helpful because I want debug messages to show up in development,
but not in production, but having all the memory logging makes it
almost impossible to pick anything else out of the log. I want the
feature available, just not on by default because it's useful in limited
circumstances.
