Added ability to initialize ListMonitors asynchronously. This is a deadlock-preventive measure for apps that heavily recreates ListMonitors while updates and saves are running in the background (because NSFetchedResultController's performFetch() locks the whole NSManagedObjectContext chain up until the NSPersistentStoreCoordinator)

CoreStore.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
     s.name = "CoreStore"
-    s.version = "1.3.3"
+    s.version = "1.3.4"
     s.license = "MIT"
     s.summary = "Unleashing the real power of Core Data with the elegance and safety of Swift"
     s.homepage = "https://github.com/JohnEstropia/CoreStore"

CoreStore/Info.plist

@@ -15,7 +15,7 @@
 	<key>CFBundlePackageType</key>
 	<string>FMWK</string>
 	<key>CFBundleShortVersionString</key>
-	<string>1.3.3</string>
+	<string>1.3.4</string>
 	<key>CFBundleSignature</key>
 	<string>????</string>
 	<key>CFBundleVersion</key>

CoreStore/Observing/CoreStore+Observing.swift

@@ -72,6 +72,30 @@ public extension CoreStore {
         return self.defaultStack.monitorList(from, queryClauses)
     }
     
+    /**
+     Using the `defaultStack`, asynchronously creates a `ListMonitor` for a list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public static func monitorList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ fetchClauses: FetchClause...) {
+        
+        self.defaultStack.monitorList(createAsynchronously: createAsynchronously, from, fetchClauses)
+    }
+    
+    /**
+     Using the `defaultStack`, asynchronously creates a `ListMonitor` for a list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public static func monitorList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ fetchClauses: [FetchClause])  {
+        
+        self.defaultStack.monitorList(createAsynchronously: createAsynchronously, from, fetchClauses)
+    }
+    
     /**
     Using the `defaultStack`, creates a `ListMonitor` for a sectioned list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list.
     
@@ -99,4 +123,30 @@ public extension CoreStore {
         
         return self.defaultStack.monitorSectionedList(from, sectionBy, fetchClauses)
     }
+    
+    /**
+     Using the `defaultStack`, asynchronously creates a `ListMonitor` for a sectioned list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter sectionBy: a `SectionBy` clause indicating the keyPath for the attribute to use when sorting the list into sections.
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public static func monitorSectionedList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ sectionBy: SectionBy, _ fetchClauses: FetchClause...) {
+        
+        self.defaultStack.monitorSectionedList(createAsynchronously: createAsynchronously, from, sectionBy, fetchClauses)
+    }
+    
+    /**
+     Using the `defaultStack`, asynchronously creates a `ListMonitor` for a sectioned list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter sectionBy: a `SectionBy` clause indicating the keyPath for the attribute to use when sorting the list into sections.
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public static func monitorSectionedList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ sectionBy: SectionBy, _ fetchClauses: [FetchClause]) {
+        
+        self.defaultStack.monitorSectionedList(createAsynchronously: createAsynchronously, from, sectionBy, fetchClauses)
+    }
 }

CoreStore/Observing/DataStack+Observing.swift

@@ -97,6 +97,45 @@ public extension DataStack {
         )
     }
     
+    /**
+     Asynchronously creates a `ListMonitor` for a list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public func monitorList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ fetchClauses: FetchClause...) {
+        
+        self.monitorList(createAsynchronously: createAsynchronously, from, fetchClauses)
+    }
+    
+    /**
+     Asynchronously creates a `ListMonitor` for a list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public func monitorList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ fetchClauses: [FetchClause])  {
+        
+        CoreStore.assert(
+            NSThread.isMainThread(),
+            "Attempted to observe objects from \(typeName(self)) outside the main thread."
+        )
+        CoreStore.assert(
+            fetchClauses.filter { $0 is OrderBy }.count > 0,
+            "A ListMonitor requires an OrderBy clause."
+        )
+        
+        _ = ListMonitor(
+            dataStack: self,
+            from: from,
+            sectionBy: nil,
+            fetchClauses: fetchClauses,
+            createAsynchronously: createAsynchronously
+        )
+    }
+    
     /**
     Creates a `ListMonitor` for a sectioned list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list.
     
@@ -138,4 +177,45 @@ public extension DataStack {
             fetchClauses: fetchClauses
         )
     }
+    
+    /**
+     Asynchronously creates a `ListMonitor` for a sectioned list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter sectionBy: a `SectionBy` clause indicating the keyPath for the attribute to use when sorting the list into sections.
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public func monitorSectionedList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ sectionBy: SectionBy, _ fetchClauses: FetchClause...) {
+        
+        self.monitorSectionedList(createAsynchronously: createAsynchronously, from, sectionBy, fetchClauses)
+    }
+    
+    /**
+     Asynchronously creates a `ListMonitor` for a sectioned list of `NSManagedObject`s that satisfy the specified fetch clauses. Multiple `ListObserver`s may then register themselves to be notified when changes are made to the list. Since `NSFetchedResultsController` greedily locks the persistent store on initial fetch, you may prefer this method instead of the synchronous counterpart to avoid deadlocks while background updates/saves are being executed.
+     
+     - parameter createAsynchronously: the closure that receives the created `ListMonitor` instance
+     - parameter from: a `From` clause indicating the entity type
+     - parameter sectionBy: a `SectionBy` clause indicating the keyPath for the attribute to use when sorting the list into sections.
+     - parameter fetchClauses: a series of `FetchClause` instances for fetching the object list. Accepts `Where`, `OrderBy`, and `Tweak` clauses.
+     */
+    public func monitorSectionedList<T: NSManagedObject>(createAsynchronously createAsynchronously: (ListMonitor<T>) -> Void, _ from: From<T>, _ sectionBy: SectionBy, _ fetchClauses: [FetchClause]) {
+        
+        CoreStore.assert(
+            NSThread.isMainThread(),
+            "Attempted to observe objects from \(typeName(self)) outside the main thread."
+        )
+        CoreStore.assert(
+            fetchClauses.filter { $0 is OrderBy }.count > 0,
+            "A ListMonitor requires an OrderBy clause."
+        )
+        
+        _ = ListMonitor(
+            dataStack: self,
+            from: from,
+            sectionBy: sectionBy,
+            fetchClauses: fetchClauses,
+            createAsynchronously: createAsynchronously
+        )
+    }
 }

CoreStore/Observing/ListMonitor.swift

@@ -885,7 +885,39 @@ public final class ListMonitor<T: NSManagedObject> {
     
     // MARK: Internal
     
-    internal init(dataStack: DataStack, from: From<T>, sectionBy: SectionBy?, fetchClauses: [FetchClause]) {
+    internal convenience init(dataStack: DataStack, from: From<T>, sectionBy: SectionBy?, fetchClauses: [FetchClause]) {
+     
+        self.init(
+            dataStack: dataStack,
+            from: from,
+            sectionBy: sectionBy,
+            fetchClauses: fetchClauses,
+            prepareFetch: { _, performFetch in performFetch() }
+        )
+    }
+    
+    internal convenience init(dataStack: DataStack, from: From<T>, sectionBy: SectionBy?, fetchClauses: [FetchClause], createAsynchronously: (ListMonitor<T>) -> Void) {
+        
+        self.init(
+            dataStack: dataStack,
+            from: from,
+            sectionBy: sectionBy,
+            fetchClauses: fetchClauses,
+            prepareFetch: { listMonitor, performFetch in
+                
+                dataStack.childTransactionQueue.async {
+                    
+                    performFetch()
+                    GCDQueue.Main.async {
+                        
+                        createAsynchronously(listMonitor)
+                    }
+                }
+            }
+        )
+    }
+    
+    private init(dataStack: DataStack, from: From<T>, sectionBy: SectionBy?, fetchClauses: [FetchClause], prepareFetch: (ListMonitor<T>, () -> Void) -> Void) {
         
         let context = dataStack.mainContext
         
@@ -927,7 +959,8 @@ public final class ListMonitor<T: NSManagedObject> {
         
         fetchedResultsControllerDelegate.handler = self
         fetchedResultsControllerDelegate.fetchedResultsController = fetchedResultsController
-        try! fetchedResultsController.performFetch()
+        
+        prepareFetch(self, { try! fetchedResultsController.performFetch() })
     }
     
     deinit {

README.md

@@ -255,7 +255,7 @@ class MyViewController: UIViewController {
 
 
 ## Migrations
-So far we have only seen `addSQLiteStoreAndWait(...)` used to initialize our persistent store. As the method name's "AndWait" suffix suggests, this method will block, even if a migration occurs. If migrations are expected, the asynchronous variant `addSQLiteStore(... completion:)` method is recommended:
+So far we have only seen `addSQLiteStoreAndWait(...)` used to initialize our persistent store. As the method name's "AndWait" suffix suggests, this method blocks so it should not do long tasks such as store migrations (in fact CoreStore won't even attempt to, and any model mismatch will be reported as an error). If migrations are expected, the asynchronous variant `addSQLiteStore(... completion:)` method should be used instead:
 ```swift
 do {
     let progress: NSProgress = try dataStack.addSQLiteStore(