This prevents a channel from being closed twice when the task manager is
closed. That same check existed to make sure a panic didn't happen when
detaching a killed query, but the check was forgotten when closing the
task manager.
This also adds a new error when attempting to kill an already killed
query.
This more accurately shows whether or not a query has been killed.
Instead of automatically removing it from the query table when it's
killed even though goroutines and iterators may still be open, it now
marks the process as killed. This should allow us to more accurately
determine if a query has been stalled and is still using resources on
the server.
This is related to #8848, but not directly connected.
There are several places in the code where comma-ok map retrieval was
being used poorly. Some were benign, like checking existence before
issuing an unconditional delete with no cleanup. Others were potentially
far more serious: assuming that if 'ok' was true, then the resulting
pointer retrieved from the map would be non-nil. `nil` is a perfectly
valid value to store in a map of pointers, and the comma-ok syntax is
meant for when membership is distinct from having a non-zero value.
There was only one or two cases that I saw that being used correctly for
maps of pointers.
This change provides a clear separation between the query engine
mechanics and the query language so that the language can be parsed and
dealt with separate from the query engine itself.
Jonathan A. Sternberg
Joe LeGasse