Router and filter instances cannot be destroyed before all worker
threads have exited. Otherwise there is a risk that data gets deleted
while someone might still be accessing it. Further, since all router
and filter instances are created by the main-thread it is better that
they are deleted by that thread as well (and not by whichever thread
happens to execute service_shutdown()). That will reduce the risk that
some unknown assumptions are violated.
The code prevented scaling by imposing global spinlocks for the DCBs and
SESSIONs. Removing this list means that a thread-local list must be taken
into use to replace it.
Because each thread has their own epoll file descriptor and only one
thread can process a DCB, it makes sense to move to a per thread zombie
queue. This removes one of the last restrictions on scalability.
The service header in include/maxscale/ contains the public part of the
service API. These functions can be safely used by the modules.
The internal header located in service/core/maxscale/ is used by the core
to initialize MaxScale at startup or to provide other services in a more
controlled way (the config_runtime, for example).
When C and C++ are mixed in a project, main() should be compiled
as C++ to ensure that all C++ static initializations are performed
properly. That may not be strictly true anymore, depending on the
used compiler and environment, but better to do that to be on the
safe side.
