Code for NSNotificationCenter subscription controlled by cancellation token.

gistfile1.txt

#import <XCTest/XCTest.h>
#import "TwistedoakCollapsingFutures.h"

#define notificationName @"note"

static int counter = 0;

@interface NSNotificationCenter (CancelToken)

-(void) addObserverForName:(NSString*)name
                     until:(TOCCancelToken*)untilCancelledToken
                usingBlock:(void(^)(NSNotification*))block;

@end
@implementation NSNotificationCenter (CancelToken)

-(void) addObserverForName:(NSString*)name
                     until:(TOCCancelToken*)untilCancelledToken
                usingBlock:(void(^)(NSNotification*))block {
    id subscription = [self addObserverForName:name
                                        object:nil
                                         queue:nil
                                    usingBlock:block];
    
    [untilCancelledToken whenCancelledDo:^{
        [self removeObserver:subscription];
    }];
}

@end

@interface Attempt : NSObject
@property int localCounter;
@end

@implementation Attempt

@synthesize localCounter;

-(id)initUntil:(TOCCancelToken*)untilCancelledToken {
    if (self = [super init]) {
        NSNotificationCenter* c = NSNotificationCenter.defaultCenter;
        [c addObserverForName:notificationName
                        until:untilCancelledToken
                   usingBlock:^(NSNotification *note) {
                       int oldCounterValue = counter;
                       counter++;
                       self.localCounter++;
                       NSAssert(counter==oldCounterValue+1, @"Atomicity guarantee violated.");
                   }];
    }
    return self;
}
@end

@interface Test2Tests : XCTestCase
@end

@implementation Test2Tests

    -(void)testExample {
        for(int i =0; i < 5; i++) {
            TOCCancelTokenSource* c = [TOCCancelTokenSource new];
            Attempt *a = [[Attempt alloc] initUntil:c.token];
            [NSNotificationCenter.defaultCenter postNotificationName:notificationName object:nil];
            [c cancel];
        
            XCTAssertEqual(counter, i+1, @"Unexpected value for counter.");
            XCTAssertEqual(1, a.localCounter, @"Unexpected value for localCounter.");
        }
    }
@end