If a vici client registered for (control-)log events, but a vici read/write
operation fails, this may result in a deadlock. The attempt to write to the
bus results in a vici log message, which in turn tries to acquire the lock
for the entry currently held.
While a recursive lock could help as well for a single thread, there is still
a risk of inter-thread races if there is more than one thread listening for
events and/or having read/write errors.
We instead log to a local buffer, and write to the bus not before the connection
entry has been released. Additionally, we mark the connection entry as unusable
to avoid writing to the failed socket again, potentially triggering an error
loop.
If do_read() returns with EWOULDBLOCK, we must ensure that we actually have
processed the full length header before checking the zero-initialized buffer
length.
While we currently have no need for messages larger than 65KB, we should design
the protocol to be future-proof, as we plan to keep at least to lowest protocol
layer stable.
To avoid any allocation issues, we currently keep the message size limit at
512KB.
Uses separate locks for socket read and write operations. While holding the
socket reader lock, a different thread can still claim the socket write lock.
This allows to asynchronously send event messages while holding the read
lock.
Andreas Steffen