Question

I want to expose an atomic property in my obj-c class, but internally I’d prefer to access it’s instance var directly rather using self.myproperty for every reference. How do you manually create a lock to block the external read?

So I want…

@property (atomic, strong) NSString *someString;

- myInternalMethodOfClassA
{
    ...
    @synchronized(someString) {
        someString = @"New string";
    }
    ...
}

…to block…

- myInstanceMethodInClientClassB 
{
    ClassA *myobj = [ClassA alloc] init];

    ...
    NSString *str = myobj.someString;
    ...
}

Answer 1

According to some chat on the Apple Objc-lang list, it’s considered a bug to have an atomic property for which you manually create one accessor and synthesize the other. The alternatives are:

1. Create both accessors yourself and use a bespoke locking object plus @synchronized(anObject), which you can then use elsewhere in your class’s code.
2. @synthesize them and always access them via their accessors (ie self.myAtomicProp internally). This is slower but most likely not a problem in nearly all cases.