Multi-threading with Graph

[JARMourato]

Hi guys, while testing your library I've made an app and installed crashlytics so I could track errors. I've come across this stack trace a couple of times now :

Thread : Crashed: com.jarm.testGraph.dataBaseQueue
0 libobjc.A.dylib 0x19938dbd0 objc_msgSend + 16
1 CoreData 0x18444210c -[NSManagedObjectContext(_NSInternalAdditions) _retainedObjectWithID:optionalHandler:withInlineStorage:] + 84
2 CoreData 0x184482f80 -[_NSFaultingMutableSet willReadWithContents:] + 576
3 CoreData 0x184464f1c -[NSFaultingMutableSet countByEnumeratingWithState:objects:count:] + 44
4 libswiftFoundation.dylib 0x101725848 TFC10Foundation15NSFastGenerator4nextfS0_FT_GSqPSs9AnyObject + 80
5 Graph 0x1005f1fa4 specialized ManagedEntity.subscript.getter (ManagedEntity.swift:64)
6 Graph 0x1005f0900 ManagedEntity.subscript.getter (ManagedEntity.swift:63)
7 Graph 0x1005c40c8 Entity.subscript.getter (Entity.swift:87)
8 testGraph 0x100089bd4 PersistanceManager.(createEntryFrom in _31C0B1288B530182F4EB108E0D3B2867)(Entity) -> Entry (PersistanceManager.swift:243)

I'm using a background thread to get the entity from Graph. So my question is: Is there a recommended way to fetch result from Graph in background threads ? Could it be done concurrently or only serially ?

Thanks for the help.

PS: IMHO this library would benefit from a detailed documentation, I don't know if that is on your backlog ;) I'd be happy to contribute to that if you like

[daniel-jonathan]

Hi :)

Can you share your code you are currently using to make the background request? As for documentation, that is something we would love help with and plan to attack this month.

[JARMourato]

It was my mistake :) was passing a wrong parameter as subscript. Sorry for opening the issue. Still i would like to know if you would recommend one instance of Graph and update it from each thread or multiple Graph instances (the latter seems odd). Example :

let graph = Graph()
for i in 0.stride(to: 1000, by: 1) {
   var q: dispatch_queue_t? =  dispatch_queue_create("com.testQueue.\(i)", DISPATCH_QUEUE_CONCURRENT)
   dispatch_async(q) { 
        let entity = Entity(type: "new")
        entity["count"] = i
        graph.save()
   } 
}

[daniel-jonathan]

Great question. I found that usually people think of connecting to databases through a singleton or some global object. I found that that approach is really bad when it comes to architectural design. So what I recommend, is that each ViewController, or module, have a private reference to graph, that it uses. No need to get anything shared.

In regards to your example code you just shared, you are creating 1000 threads and saving the entities in each thread. Is this a test to check the threading? If not, it would be better to do it in one thread, call the save once and go from there. For example:

var q: dispatch_queue_t? =  dispatch_queue_create("com.testQueue.\(i)", DISPATCH_QUEUE_CONCURRENT)

dispatch_async(q) {
    let graph = Graph()

    for i in 0.stride(to: 1000, by: 1) {
        let entity = Entity(type: "new")
        entity["count"] = i
    }       

    graph.save()
}

The other thing to note, is that graph has an asyncSave method. I didn't test the code, but that should be the general idea.

Another tip, is that Graph doesn't require synchronization. It is always synchronized. Deep down in the code that makes Graph, there is ever a single instance of the Context, Coordinator, and such that ensure this.

:)

[JARMourato]

Yes, it was just to test threading. Thanks for the answer! It seems strange to me have an individual private reference since I'm used to CoreData as is and to the rather abused Objective-C"ish" Singleton (anti)-pattern.

I really think that Graph is going to be very successful. Its simple and powerful!

[daniel-jonathan]

Thank you! We really appreciate it. If you feel this issue is resolved, please close it. If you would like, and I invite you, open more issues with some more interesting questions :)

[JARMourato]

Will do. Changed the title of the issue for future reference. :)

[daniel-jonathan]

Thank you :)

---

Daniel Dahan

M: +1 647.627.0770
Skype: djondahan

On Mar 3, 2016, at 9:51 AM, JARMourato notifications@github.com wrote:

Will do. Changed the title of the issue for future reference. :)

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