additional safety for transactions by splitting between sync and async subclasses

HardcoreData/AsynchronousDataTransaction.swift

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+//
+//  AsynchronousDataTransaction.swift
+//  HardcoreData
+//
+//  Copyright (c) 2015 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import GCDKit
+
+
+/**
+The AsynchronousDataTransaction provides an interface for NSManagedObject creates, updates, and deletes. A transaction object should typically be only used from within a transaction block initiated from DataStack.performTransaction(_:), or from HardcoreData.performTransaction(_:).
+*/
+public class AsynchronousDataTransaction: DataTransaction {
+    
+    // MARK: Public
+    
+    /**
+    Saves the transaction changes asynchronously. Note that this method should not be used after either the commit(_:) or commitAndWait() method was already called once.
+    
+    :param: completion the block executed after the save completes. Success or failure is reported by the SaveResult argument of the block.
+    */
+    public func commit(completion: (result: SaveResult) -> Void) {
+        
+        HardcoreData.assert(self.transactionQueue.isCurrentExecutionContext() == true, "Attempted to commit a \(self.dynamicType) outside a transaction queue.")
+        HardcoreData.assert(!self.isCommitted, "Attempted to commit a \(self.dynamicType) more than once.")
+        
+        self.isCommitted = true
+        let semaphore = GCDSemaphore(0)
+        self.context.saveAsynchronouslyWithCompletion { (result) -> Void in
+            
+            self.result = result
+            completion(result: result)
+            semaphore.signal()
+        }
+        semaphore.wait()
+    }
+    
+    /**
+    Saves the transaction changes and waits for completion synchronously. Note that this method should not be used after either the commit(_:) or commitAndWait() method was already called once.
+    
+    :returns: a SaveResult value indicating success or failure.
+    */
+    public func commitAndWait() {
+        
+        HardcoreData.assert(self.transactionQueue.isCurrentExecutionContext() == true, "Attempted to commit a \(self.dynamicType) outside a transaction queue.")
+        HardcoreData.assert(!self.isCommitted, "Attempted to commit a \(self.dynamicType) more than once.")
+        
+        self.isCommitted = true
+        self.result = self.context.saveSynchronously()
+    }
+    
+    /**
+    Begins a child transaction synchronously where NSManagedObject creates, updates, and deletes can be made.
+    
+    :param: closure the block where creates, updates, and deletes can be made to the transaction. Transaction blocks are executed serially in a background queue, and all changes are made from a concurrent NSManagedObjectContext.
+    :returns: a SaveResult value indicating success or failure, or nil if the transaction was not comitted synchronously
+    */
+    public func performTransactionAndWait(closure: (transaction: SynchronousDataTransaction) -> Void) -> SaveResult? {
+        
+        return SynchronousDataTransaction(
+            mainContext: self.context,
+            queue: self.childTransactionQueue,
+            closure: closure).performAndWait()
+    }
+    
+    
+    // MARK: Internal
+    
+    internal init(mainContext: NSManagedObjectContext, queue: GCDQueue, closure: (transaction: AsynchronousDataTransaction) -> Void) {
+        
+        self.closure = closure
+        
+        super.init(mainContext: mainContext, queue: queue)
+    }
+    
+    internal func perform() {
+        
+        self.transactionQueue.async {
+            
+            self.closure(transaction: self)
+            if !self.isCommitted {
+                
+                HardcoreData.log(.Warning, message: "The closure for the \(self.dynamicType) completed without being committed. All changes made within the transaction were discarded.")
+            }
+        }
+    }
+    
+    internal func performAndWait() -> SaveResult? {
+        
+        self.transactionQueue.sync {
+            
+            self.closure(transaction: self)
+            if !self.isCommitted {
+                
+                HardcoreData.log(.Warning, message: "The closure for the \(self.dynamicType) completed without being committed. All changes made within the transaction were discarded.")
+            }
+        }
+        return self.result
+    }
+    
+    
+    // MARK: Private
+    
+    private let closure: (transaction: AsynchronousDataTransaction) -> Void
+}