Instruments memory leaks detecting issue in Xcode 6.2

Question

everyone! I'm using Xcode 6.2 now for developing objective-c, when i try to use "Instruments" to detecting memory issues, it just not work as i were see books or blogs.I use the code blow to test(main function is omitted, using default xcode&instruments settings).

for(int i=0; i<2; i++)
{
    KSTestObj *obj0 = [[KSTestObj alloc] init];
    KSTestObj *obj1 = [[KSTestObj alloc] init];
    obj0.obj = obj1;
    obj1.obj = obj0;
}
sleep(100);

and the KSTestObj class just has a NSObject propety. Here is a strange phenomenon. When I set i<1, the "Instruments" capture nothing, and when i<2(or bigger), it can detect a memory problem by Leaks! BUT the leaked objects number is 2(or 2*times-2)!Thats ODD! Anyone knows what going on? Did i made any mistakes? tks! here is the picture & log: i<2, and "Instruments" detect 2 object leaked.

2015-06-27 14:33:19.108 ObjCPro_Test[50820:603] init success! 0x7ff968700c10
2015-06-27 14:33:19.109 ObjCPro_Test[50820:603] init success! 0x7ff968700c20
2015-06-27 14:33:19.109 ObjCPro_Test[50820:603] init success! 0x7ff9687003a0
2015-06-27 14:33:19.110 ObjCPro_Test[50820:603] init success! 0x7ff9687003b0
<End of Run>

enter image description here

i<1, "Instruments" shows no leaked objects!

2015-06-27 14:30:17.737 ObjCPro_Test[50789:603] init success! 0x7f7ff1e00830
2015-06-27 14:30:17.738 ObjCPro_Test[50789:603] init success! 0x7f7ff1e004e0
<End of Run>

enter image description here

Unknown Unknown · Accepted Answer · 2015-06-27T22:08:34

If obj0 contains a strong reference to obj1, and obj1 also contains a strong reference to obj0, you've created a retain cycle, where neither object can be released.

This will leak memory, for each object, for each iteration through the loop. (That's exactly why it's 2 x number of iterations - 1.)

To solve this, you could set the obj property to weak, so each object can go out of existence at the conclusion of an iteration.

Instruments memory leaks detecting issue in Xcode 6.2

1 Answers