check_depend() bug-report & fix

[Philipp Berndt]

Hi,

the dependency checking in monit-4.6 falsely assumes that the inter-service 
dependencies constitute a TREE.

With a simple configuration like this

snip

check file A with path /tmp/A

check file B with path /tmp/B
   depends on A

check file C with path /tmp/C
   depends on A

check file D with path /tmp/D
   depends on B, C

snap

this leads monit to believe there was a dependency loop:

$ monit -t
monit: Error: Found a depend loop in the control file involving the service 
'B'

Instead, the dependency structure forms a directed acyclic graph (dag).

In the attached patch I have replaced check_depend(), validate_depend() and 
order_depend() by an implementation that does a topological sort of the 
dependency dag, thereby finding any (real) cycles and putting the services in 
the required order.

Regards,
Philipp Berndt

monit-4.6.toposort.patch
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