Is there a way to “find mystery retains” …?

Question

Recently I was repairing someone\'s code. There was a big class that would not dealloc. You\'d have to hit it with 5 or 6 releases to get it to dealloc.

I carefully

Answer 1

Instruments can show you the call stack for every malloc, release, and retain for any Obj-C object in your app with no code changes required. It works when you're using ARC, which is not the case for the solution from fabio.

It's really useful for finding those mystery retains - e.g. when an object just won't dealloc when it should.

Here's how:

• CMD + I (Product / Profile)
• When Instruments pops up choose 'Allocations' (NOT Leaks)
• Your app should run.
• Do whatever causes your mystery retains to happen.
• Select the 'Allocation' instrument on the left-hand panel.
• Press CMD + 1 or select the circle with the wave in it on the right. In the panel on the lower right, tick the 'Record reference counts' option. This is important, or only mallocs and frees will be recorded.
• In the search box on the top-right of the list, type the name of your class (e.g. BCMyObject).
• This filters the list of 'Statistics' to show how many instances of your class are currently live. The #Persistent column shows how many instances are live.
• Click the row, and then the little arrow -> next to the class name. You'll see the breadcrumbs shows 'Statistics > Allocation Summary > BCMyobject'
• This shows you all the instances of said class (and which ones are live).
• Select an instance, and click the arrow again (this time by address)
• Now you'll see 'Statistics > Allocation Summary > BCMyObject > History: 0xADDRESS' in the breadcrumps.
• This'll list every time the object is malloc'd retained or released.
• Now in the left panel where the 'Record Reference Counts' option was, press the icon that looks like a bar with boxes connected to it or press CMD + 3.
• Select one of the rows and you'll see the complete call stack that led to the call.

Easy! (ish)