Static BOOL thread safety with class methods

XYZManager+Additions.m

// Old using NSLock.
#import "XYZManager+Additions.h"

@implementation XYZManager (Additions_old)

static BOOL setup = NO;
static NSLock  *setupLock = [NSLock new];

+ (void)xyz_setupSuccessful:(BOOL)success {
    [setupLock lock];
    setup = success;
    [setupLock unlock];
}

+ (void)xyz_clearSuccessful:(BOOL)success {
    [setupLock lock];
    setup = success ? NO : setup;
    [setupLock unlock];    
}

+ (BOOL)xyz_isSetupSuccessful {
    return setup;
}

@end

    
// Modern queue based locking
#import "XYZManager+Additions.h"

@implementation XYZManager (Additions_new)

static BOOL setup = NO;

static dispatch_queue_t xyz_setupStateSetterQueue() {
    static dispatch_queue_t setupQueue;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        setupQueue = dispatch_queue_create("com.xyz.setup.queue", DISPATCH_QUEUE_SERIAL );
    });
    return setupQueue;
}

+ (void)xyz_setupSuccessful:(BOOL)success {
    dispatch_sync(xyz_setupStateSetterQueue(), ^{
        setup = success;
    });
}

+ (void)xyz_clearSuccessful:(BOOL)success {
    dispatch_sync(xyz_setupStateSetterQueue(), ^{
        setup = success ? NO : setup;;
    });
}

+ (BOOL)xyz_isSetupSuccessful {
    return setup;
}

@end