Simple implementation of a thread safe mutable dictionary. In most cases, you want NSCache instead, but it can be useful in situations where you want to manually control what is evicted from the cache in low memory situations.**Warning:** I only use this for setting/getting keys. Enumeration is not thread safe here and will still throw exception…

PSPDFThreadSafeMutableDictionary.m

//
// PSPDFThreadSafeMutableDictionary.m
//
// Copyright (c) 2013 Peter Steinberger, PSPDFKit GmbH. All rights reserved.
//
// 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/Foundation.h>

// Dictionary-Subclasss whose primitive operations are thread safe.
@interface PSPDFThreadSafeMutableDictionary : NSMutableDictionary
@end

// ----------------------------------------------------------------

//
//  PSPDFThreadSafeMutableDictionary.m
//  PSPDFKit
//
//  Copyright (c) 2013 PSPDFKit GmbH. All rights reserved.
//

#import "PSPDFThreadSafeMutableDictionary.h"
#import <libkern/OSAtomic.h>

#define LOCKED(...) OSSpinLockLock(&_lock); \
__VA_ARGS__; \
OSSpinLockUnlock(&_lock);

@implementation PSPDFThreadSafeMutableDictionary {
    OSSpinLock _lock;
    NSMutableDictionary *_dictionary; // Class Cluster!
}

///////////////////////////////////////////////////////////////////////////////////////////
#pragma mark - NSObject

- (id)init {
    return [self initWithCapacity:0];
}

- (id)initWithObjects:(NSArray *)objects forKeys:(NSArray *)keys {
    if ((self = [self initWithCapacity:objects.count])) {
        [objects enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
            _dictionary[keys[idx]] = obj;
        }];
    }
    return self;
}

- (id)initWithCapacity:(NSUInteger)capacity {
    if ((self = [super init])) {
        _dictionary = [[NSMutableDictionary alloc] initWithCapacity:capacity];
        _lock = OS_SPINLOCK_INIT;
    }
    return self;
}

///////////////////////////////////////////////////////////////////////////////////////////
#pragma mark - NSMutableDictionary

- (void)setObject:(id)anObject forKey:(id<NSCopying>)aKey {
    LOCKED(_dictionary[aKey] = anObject)
}

- (void)addEntriesFromDictionary:(NSDictionary *)otherDictionary {
    LOCKED([_dictionary addEntriesFromDictionary:otherDictionary]);
}

- (void)setDictionary:(NSDictionary *)otherDictionary {
    LOCKED([_dictionary setDictionary:otherDictionary]);
}

- (void)removeObjectForKey:(id)aKey {
    LOCKED([_dictionary removeObjectForKey:aKey])
}

- (void)removeAllObjects {
    LOCKED([_dictionary removeAllObjects]);
}

- (NSUInteger)count {
    LOCKED(NSUInteger count = _dictionary.count)
    return count;
}

- (NSArray *)allKeys {
    LOCKED(NSArray *allKeys = _dictionary.allKeys)
    return allKeys;
}

- (NSArray *)allValues {
    LOCKED(NSArray *allValues = _dictionary.allValues)
    return allValues;
}

- (id)objectForKey:(id)aKey {
    LOCKED(id obj = _dictionary[aKey])
    return obj;
}

- (NSEnumerator *)keyEnumerator {
    LOCKED(NSEnumerator *keyEnumerator = [_dictionary keyEnumerator])
    return keyEnumerator;
}

- (id)copyWithZone:(NSZone *)zone {
    return [self mutableCopyWithZone:zone];
}

- (id)mutableCopyWithZone:(NSZone *)zone {
    LOCKED(id copiedDictionary = [[self.class allocWithZone:zone] initWithDictionary:_dictionary])
    return copiedDictionary;
}

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state
                                  objects:(id __unsafe_unretained [])stackbuf
                                    count:(NSUInteger)len {
    LOCKED(NSUInteger count = [[_dictionary copy] countByEnumeratingWithState:state objects:stackbuf count:len]);
    return count;
}

- (void)performLockedWithDictionary:(void (^)(NSDictionary *dictionary))block {
    if (block) LOCKED(block(_dictionary));
}

- (BOOL)isEqual:(id)object {
    if (object == self) return YES;

    if ([object isKindOfClass:PSPDFThreadSafeMutableDictionary.class]) {
        PSPDFThreadSafeMutableDictionary *other = object;
        __block BOOL isEqual = NO;
        [other performLockedWithDictionary:^(NSDictionary *dictionary) {
            [self performLockedWithDictionary:^(NSDictionary *otherDictionary) {
                isEqual = [dictionary isEqual:otherDictionary];
            }];
        }];
        return isEqual;
    }
    return NO;
}

@end