Making NSDateFormatter thread safe

NSDate+AGCategory.h

//
//  NSDate+AGCategory.h
//  AGFoundation
//
//  Created by Andrew Garn on 23/07/2012.
//  Copyright (c) 2012 Andrew Garn. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSDate (AGCategory)

+ (NSDateFormatter *)dateFormatterWithDateFormat:(NSString *)dateFormat;

@end

NSDate+AGCategory.m

//
//  NSDate+AGCategory.m
//  AGFoundation
//
//  Created by Andrew Garn on 23/07/2012.
//  Copyright (c) 2012 Andrew Garn. All rights reserved.
//

#import "NSDate+AGCategory.h"

@implementation NSDate (AGCategory)

+ (NSDateFormatter *)dateFormatterWithDateFormat:(NSString *)dateFormat
{
    NSMutableDictionary *threadDictionary = [[NSThread currentThread] threadDictionary];
    NSString *threadDictionaryKey = [NSString stringWithFormat:@"NSDateAGCategoryDateFormatter-%@", dateFormat];
    
    NSDateFormatter *dateFormatter = [threadDictionary objectForKey:threadDictionaryKey];
    if (dateFormatter == nil)
    {
	dateFormatter = [[NSDateFormatter alloc] init];
	[dateFormatter setCalendar:[NSCalendar currentCalendar]];
        [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
	[threadDictionary setObject:dateFormatter forKey:threadDictionaryKey];
    }
    
    // Ensure the dateformatter is using the correct format.
    if (![[dateFormatter dateFormat] isEqualToString:dateFormat])
        [dateFormatter setDateFormat:dateFormat];
	
    // Reset the timeZone that the dateFormatter uses.
    if (![[dateFormatter timeZone] isEqual:[NSTimeZone localTimeZone]])
        [dateFormatter setTimeZone:[NSTimeZone localTimeZone]];
    
    // Reset the locale that the dateFormatter uses.
    if (![[dateFormatter locale] isEqual:[NSLocale autoupdatingCurrentLocale]])
        [dateFormatter setLocale:[NSLocale autoupdatingCurrentLocale]];
    
    return dateFormatter;
}