A thread safe way to parse dates with arbitrary formats. NSDateFormatter is not thread safe. This method keeps a collection of formatters, one per thread per format, and creates/returns them in a thread safe manner. Caching formatter objects results in a significant speed improvement. On the simulator (2.4Ghz i5) we see the following numbers: Fo…

NSDateFormatter+fbsThreadSafeFormatter.h

//
//  NSDateFormatter+fbsThreadSafeFormatter.h
//  NSDateAdditions
//
//  Created by Patrick Hughes on 3/3/13.
//  Copyright (c) 2013 Patrick Hughes. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSDateFormatter (fbsThreadSafeFormatter)

// NSDateFormatter is not thread safe. This method keeps a collection of formatters,
// one per thread per format, and creates/returns them in a thread safe manner.
/*  Caching formatter objects results in a significant speed improvement. 
	On the simulator (2.4Ghz i5) we see the following numbers:
	Formatting 10,000 date objects (single format, multiple threads):
	Creating new formatter each time: 23.019063 seconds.
	One formatter per thread: 1.352597 seconds. 
*/
+ (NSDateFormatter*)fbsFormatterWithFormat:(NSString*)format;
+ (NSDateFormatter*)fbsFormatterWithFormat:(NSString*)format usingTimeZoneAbbreviation:(NSString*)abbreviation;

NSDateFormatter+fbsThreadSafeFormatter.m

//
//  NSDateFormatter+fbsThreadSafeFormatter.m
//  NSDateAdditions
//
//  Created by Patrick Hughes on 3/3/13.
//  Copyright (c) 2013 Patrick Hughes. All rights reserved.
//

#import "NSDateFormatter+fbsThreadSafeFormatter.h"
#import <objc/runtime.h>

static char const * const formattersKey = "formattersKey";
static char const * const lockKey = "lockKey";

@implementation NSDateFormatter (fbsThreadSafeFormatter)

+ (NSDateFormatter*)fbsFormatterWithFormat:(NSString*)format
{
  NSTimeZone *tz = [NSTimeZone localTimeZone];
	
	return [self fbsFormatterWithFormat:format usingTimeZoneAbbreviation:[tz abbreviation]];
}

+ (NSDateFormatter*)fbsFormatterWithFormat:(NSString*)format usingTimeZoneAbbreviation:(NSString*)abbreviation
{
	NSCache *formatters = objc_getAssociatedObject(self, formattersKey);
	NSLock *lock = objc_getAssociatedObject(self, lockKey);
	
	if (!formatters) {
		formatters = [[NSCache alloc] init];
		objc_setAssociatedObject(self, formattersKey, formatters, OBJC_ASSOCIATION_RETAIN);
	}
	if (!lock) {
		lock = [[NSLock alloc] init];
		objc_setAssociatedObject(self, lockKey, lock, OBJC_ASSOCIATION_RETAIN);
	}
	
	// Create a key for the formatter based on the current thread's address and the desired format.
	NSString *key = [NSString stringWithFormat:@"%p%@%@", [NSThread currentThread], abbreviation, format];
	
	[lock lock];
	NSDateFormatter *formatter = [formatters objectForKey:key];
	if (!formatter) {
		formatter = [[NSDateFormatter alloc] init];
		[formatter setDateFormat:format];
		[formatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:abbreviation]];
		
		[formatters setObject:formatter forKey:key];
	}
	[lock unlock];
	
	return formatter;
}
@end