NSManagedObjectContext for iOS 4. Maybe?

NSManagedObjectContextShim.h

/*
 NSManagedObjectContextShim.h
 NSManagedObjectContextShim
 
 Created by Daniel Tull on 25.07.2012.
 
 
 
 Copyright (c) 2012 Daniel Tull. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 
 * Redistributions of source code must retain the above copyright notice, this
 list of conditions and the following disclaimer.
 
 * Redistributions in binary form must reproduce the above copyright notice,
 this list of conditions and the following disclaimer in the documentation
 and/or other materials provided with the distribution.
 
 * Neither the name of the author nor the names of its contributors may be used
 to endorse or promote products derived from this software without specific
 prior written permission.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#import <CoreData/CoreData.h>

@interface NSManagedObjectContext (Shim)

// The returned context is guaranteed to implement -performBlock: and -performBlockAndWait: on older OS releases that predate Core Data's own ability for this
+ (NSManagedObjectContext *)dct_contextWithConcurrencyType:(NSManagedObjectContextConcurrencyType)ct;

@end

NSManagedObjectContextShim.m

/*
 NSManagedObjectContextShim.m
 NSManagedObjectContextShim
 
 Created by Daniel Tull on 25.07.2012.
 
 
 
 Copyright (c) 2012 Daniel Tull. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 
 * Redistributions of source code must retain the above copyright notice, this
 list of conditions and the following disclaimer.
 
 * Redistributions in binary form must reproduce the above copyright notice,
 this list of conditions and the following disclaimer in the documentation
 and/or other materials provided with the distribution.
 
 * Neither the name of the author nor the names of its contributors may be used
 to endorse or promote products derived from this software without specific
 prior written permission.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#import "NSManagedObjectContextShim.h"


@interface DCTThreadedManagedObjectContext : NSManagedObjectContext
{
  @private
    NSOperationQueue    *_operationQueue;
}
@end


@implementation NSManagedObjectContext (Shim)

+ (NSManagedObjectContext *)dct_contextWithConcurrencyType:(NSManagedObjectContextConcurrencyType)ct;
{
    if ([self instancesRespondToSelector:@selector(initWithConcurrencyType:)])
    {
        return [[[self alloc] initWithConcurrencyType:ct] autorelease];
    }
    else if (ct == NSConfinementConcurrencyType)
    {
        return [[[self alloc] init] autorelease];
    }
    else
    {
        return [[[DCTThreadedManagedObjectContext alloc] initWithConcurrencyType:ct] autorelease];
    }
}

@end


@implementation DCTThreadedManagedObjectContext

- (id)initWithConcurrencyType:(NSManagedObjectContextConcurrencyType)ct;
{
    // Create a queue matching the concurrency type
    NSOperationQueue *queue;
    switch (ct)
    {
        case NSPrivateQueueConcurrencyType:
        {
            queue = [NSOperationQueue new];
            [queue setMaxConcurrentOperationCount:1];
        
            break;
        }
        case NSMainQueueConcurrencyType:
        {
            queue = [[NSOperationQueue mainQueue] retain];
            
            // If called on main thread, must do work immediately to avoid deadlock
            if ([NSThread isMainThread])
            {
                if (self = [self init])
                {
                    _operationQueue = queue;
                }
                return self;
            }
            
            break;
        }
        default:
            return [self init];
    }
    
    // Bounce the initialisation over to correct queue so context knows which it's associated with
    __block DCTThreadedManagedObjectContext *myself = self;
    NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
        myself = [self init];
    }];
    
    [queue addOperation:blockOperation];
    [blockOperation waitUntilFinished];
    
    
	if ((self = myself))
    {
        _operationQueue = queue;
    }
	return self;
}

- (void)dealloc
{
    [_operationQueue release];
    [super dealloc];
}

- (void)performBlock:(void(^)())block
{
	[_operationQueue addOperationWithBlock:block];
}

- (void)performBlockAndWait:(void(^)())block
{
	NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:block];
	[_operationQueue addOperation:blockOperation];
	[blockOperation waitUntilFinished];
}

@end