The monitor now detects when a server has changed such that a replication
graph rebuild is needed and only then rebuilds the graph and detects
cycles and master.
Also, some old code is no longer called in the monitor cycle. It will be
removed in later commits. Refactored some of the related functions.
MonitorInstanceSimple is intended for simple monitors that
probe servers in a straightforward fashion. More complex monitors
can be derived directly from MonitorInstance.
Tracking how many times the monitor has performed its monitoring allows
the test framework to consistently wait for an event instead of waiting
for a hard-coded time period. The MaxCtrl `api get` command can be used to
easily extract the numeric value.
Start/stop now provided by MonitorInstance. The thread main
function is now virtual and overriden by MariaDBMonitor. Some
additional refactoring is necessary in order to be able to allow
MonitorInstance to handle the main loop.
This makes the code clearer and reduces race conditions, as the monitor
could be writing SERVER->status while a router is reading it. Also,
the time during which the SERVER struct is locked drops to a fraction.
If the feature is enabled (default off), at the end of a monitor loop
(once server states are known), read_only is enabled on slaves servers
without it.
The logic was weird, as the permission checking function assumes a disconnected
server as fine. The checking is now done when starting the main loop and lacking
grants print errors but does not stop the monitor.
Since monitors are now freed at MaxScale exit, the server data should be freed. Also,
gtid domain variables are now initialized with a common constant.
StartMonitor() now takes a MXS_MONITOR_INSTANCE and returns
true, if the monitor could be started and false otherwise.
So, the setup is such that in createInstance(), the instance
data is created and then using startMonitor() and stopMonitor()
the monitor is started/stopped. Finally in destroyInstance(),
the actual instance data is deleted.
The following type name changes
MXS_MONITOR_OBJECT -> MXS_MONITOR_API
MXS_SPECIFIC_MONITOR -> MXS_MONITOR_INSTANCE
Further, the 'handle' instance variable of what used to be
called MXS_MONITOR_OBJECT has been renamed to 'api'.
An example, what used to look like
mon->module->stopMonitor(mon->handle);
now looks like
mon->api->stopMonitor(mon->instance);
which makes it more obvious what is going on.
CreateInstance() (renamed from initMonitor()) and destroyInstance()
(renamed from finishMonitor()) have now tentatively been
implemented for all monitors.
Next step is to
1) change the prototype of startMonitor() to
bool (*startMonitor)(MXS_SPECIFIC_MONITOR*,
const MXS_MONITOR_PARAMETER*);
and assume that mon->handle will always contain the
instance,
2) not delete any data in stopMonitor(),
3) add monitorCreateAll() that calls createInstance() for all
monitors (and call that in main()), and
4) add monitorDestroyAll() that calls destroyInstance() for
all monitors (and call that in main()).
