保持周期和仪器

Question

I just wrote this retain cycle:

#import <Foundation/Foundation.h>
#import "Driver.h"
#import "Car.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Driver *driver = [[Driver alloc] init];
        Car *car = [[Car alloc] init];

        driver.car = car;
        car.driver = driver;
    }
    sleep(100);
    return 0;
}

Obviously, Driver and Car have strong properties.

Anyway, Instruments is not showing the retain cycle up in Leaks -> Cycles & Roots on Xcode 6.1.

It's a retain cycle, right? What's happening then?

Answer 1

Retain cycles are not leaks. Leak occurs when you lost track (reference) of the object. Since both objects have references to the other, it is not considered as a leak. Retain cycles are harder to find than leaks because of that. It depends on your code, and you should be careful.

Answer 2

Okay, It's working now:

@autoreleasepool {
    Driver *driver = [[Driver alloc] init];
    Car *car = [[Car alloc] init];

    driver.car = car;
    car.driver = driver;

    driver = nil;
    car = nil;

    for (size_t i = 0; i < 100000; i++) {
        driver = [[Driver alloc] init];
        car = [[Car alloc] init];
    }
}

With this code, Instruments shows the cycle on Leaks.