- There is way too much of busy waiting for fairly arbitrarily chosen
  timeout periods in the code.

  With "busy wait" here I of course don't mean *real* busy wait that
  would actually mindlessly spin the CPU.

  I mean calling poll() with some short timeout (order of seconds),
  and each time a timeout happens (which surely is the large majority
  of times), check a condition, which in the large majority of times
  will not be true, and then repeat.

  Instead the code could use for instance eventfds to enable the
  poll() calls to be without timeout. Or something similar, depending
  on case.

- Recursive mutexes are evil. In general, I think the consensus is
  that recursive mutexes should be avoided. One should use them only
  when absolutely necessary because the code-base is so complex that
  one has no idea how it works. That was hopefully not the case when
  recursive mutexes were introduced here? But probably it is by now...

- Occasionally Control-C (SIGINT) doesn't shut fown loolwsd. One has
  to kill it with SIGKILL. Which of course leaves all the chroot jails
  around.

- There are lots of places where a std::string variable is defined,
  initialised with a value, that is never changed. (In many cases it
  is const, so could of course not be changed.) Then the variable is
  used just once or twice, passed as a parameter to a function, or
  used in a comparisin expression. This is fairly pointless and just
  makes the code harder to read. Use string literals instead.

- ASCII art? Seriously?