I'm on a MacBook Pro with a 4-core i7.
I'm writing a throwaway command-line tool that builds a Core Data store
(SQLite) with (i entity_A) each related to-many to (j entity_B) each related
to-many to (k entity_C).
For large j or k, this takes a really, really long time. So I tried this:
- Create an NSOperationQueue, leaving maxConcurrentOperationCount at the
default (0), which I understand means that the queue will absorb as many
threads as the system can cope with.
- Observe NSManagedObjectContextDidSaveNotification, handled by a method that
sends mergeChangesFromContextDidSaveNotification: to the main
NSManagedObjectContext.
- In a loop running i times
-- create an NSBlockOperation, with a block that
--- peels off its own NSManagedObjectContext (NSConfinementConcurrencyType)
from the common store coordinator,
--- inserts one entity_A
--- cascades to the j entity_Bs and j*k entity_Cs.
--- It saves the MOC at the end of every entity_B loop.
-- Add the block operation to the queue
- Run the main run loop (runUntilDate: 1 second from now) until the queue's
operationCount is 0.
I set j and k too high, and had to go home for the weekend, so I've never
allowed the process to run to completion.
However, I see this in the debugger's CPU display: For a few seconds, eight
threads run concurrently, saturating the processor capacity. Then each thread
gets only about 25% duty; no more than two execute at the same time. Obviously,
something is serializing the process. I'm guessing that this comes at the
merge-changes step, but it's only a guess, and I haven't had time to
investigate.
Two-at-a-time processing is better than one-at-a-time, but it's not what I
thought I'd asked for.
I have another command-line tool that does saturate the capacity (though it was
on a 12-core machine, and I asked for only 6).
Does anyone see what's going on?
— F
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