I’m currently struggling with a core data issue with my app that defies (my) logic. I’m sure I’m doing something wrong but can’t see what.
I am doing a basic executeFetchRequest on my core data entity, but the array of managed objects returned never seems to be released ONLY when I run it on the iPhone, under the simulator it works exactly as expected.
This is despite using an NSAutoreleasePool to ensure the memory footprint is minimised. I have also checked with Instruments and there are no leaks, just ever increasing allocations of memory (by ‘[NSManagedObject(_PFDynamicAccessorsAndPropertySupport) allocWithEntity:]’). In my actual app this eventually leads to a didReceiveMemoryWarning call.
I have produced a minimal program that reproduces the problem below. I have tried various things such as faulting all the objects before draining the pool, but with no joy. If I provide an NSError pointer to the fetch no error is returned. There are no background threads running.
#import <mach/mach.h>
#import <mach/mach_host.h>
+(natural_t) get_free_memory {
mach_port_t host_port;
mach_msg_type_number_t host_size;
vm_size_t pagesize;
host_port = mach_host_self();
host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
host_page_size(host_port, &pagesize);
vm_statistics_data_t vm_stat;
if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) {
NSLog(@"Failed to fetch vm statistics");
return 0;
}
/* Stats in bytes */
natural_t mem_free = vm_stat.free_count * pagesize;
return mem_free;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Set up the edit and add buttons.
self.navigationItem.leftBarButtonItem = self.editButtonItem;
UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(insertNewObject)];
self.navigationItem.rightBarButtonItem = addButton;
[addButton release];
// Obtain the Managed Object Context
NSManagedObjectContext *context = [(id)[[UIApplication sharedApplication] delegate] managedObjectContext];
// Check the free memory before we start
NSLog(@"INITIAL FREEMEM: %d", [RootViewController get_free_memory]);
// Loop around a few times
for(int i=0; i<20; i++) {
// Create an autorelease pool just for this loop
NSAutoreleasePool *looppool = [[NSAutoreleasePool alloc] init];
// Check the free memory each time around the loop
NSLog(@"FREEMEM: %d", [RootViewController get_free_memory]);
// Create a minimal request
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:@"TestEntity" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
// Perform the fetch
NSArray *array = [context executeFetchRequest:request error:nil];
[request release];
// Drain the pool - should release the fetched managed objects?
[looppool drain];
}
// Check the free menory at the end
NSLog(@"FINAL FREEMEM: %d", [RootViewController get_free_memory]);
}
When I run the above on the simulator I get the following output (which looks reasonable to me):
2011-06-06 09:50:28.123 renniksoft[937:207] INITIAL FREEMEM: 14782464
2011-06-06 09:50:28.128 renniksoft[937:207] FREEMEM: 14807040
2011-06-06 09:50:28.135 renniksoft[937:207] FREEMEM: 14831616
2011-06-06 09:50:28.139 renniksoft[937:207] FREEMEM: 14852096
2011-06-06 09:50:28.142 renniksoft[937:207] FREEMEM: 14872576
2011-06-06 09:50:28.146 renniksoft[937:207] FREEMEM: 14897152
2011-06-06 09:50:28.149 renniksoft[937:207] FREEMEM: 14917632
2011-06-06 09:50:28.153 renniksoft[937:207] FREEMEM: 14938112
2011-06-06 09:50:28.158 renniksoft[937:207] FREEMEM: 14962688
2011-06-06 09:50:28.161 renniksoft[937:207] FREEMEM: 14983168
2011-06-06 09:50:28.165 renniksoft[937:207] FREEMEM: 14741504
2011-06-06 09:50:28.168 renniksoft[937:207] FREEMEM: 14770176
2011-06-06 09:50:28.174 renniksoft[937:207] FREEMEM: 14790656
2011-06-06 09:50:28.177 renniksoft[937:207] FREEMEM: 14811136
2011-06-06 09:50:28.182 renniksoft[937:207] FREEMEM: 14831616
2011-06-06 09:50:28.186 renniksoft[937:207] FREEMEM: 14589952
2011-06-06 09:50:28.189 renniksoft[937:207] FREEMEM: 14610432
2011-06-06 09:50:28.192 renniksoft[937:207] FREEMEM: 14630912
2011-06-06 09:50:28.194 renniksoft[937:207] FREEMEM: 14651392
2011-06-06 09:50:28.197 renniksoft[937:207] FREEMEM: 14671872
2011-06-06 09:50:28.200 renniksoft[937:207] FREEMEM: 14692352
2011-06-06 09:50:28.203 renniksoft[937:207] FINAL FREEMEM: 14716928
However, when I run it on an actual iPhone 4 (4.3.3) I get the following result:
2011-06-06 09:55:54.341 renniksoft[4727:707] INITIAL FREEMEM: 267927552
2011-06-06 09:55:54.348 renniksoft[4727:707] FREEMEM: 267952128
2011-06-06 09:55:54.702 renniksoft[4727:707] FREEMEM: 265818112
2011-06-06 09:55:55.214 renniksoft[4727:707] FREEMEM: 265355264
2011-06-06 09:55:55.714 renniksoft[4727:707] FREEMEM: 264892416
2011-06-06 09:55:56.215 renniksoft[4727:707] FREEMEM: 264441856
2011-06-06 09:55:56.713 renniksoft[4727:707] FREEMEM: 263979008
2011-06-06 09:55:57.226 renniksoft[4727:707] FREEMEM: 264089600
2011-06-06 09:55:57.721 renniksoft[4727:707] FREEMEM: 263630848
2011-06-06 09:55:58.226 renniksoft[4727:707] FREEMEM: 263168000
2011-06-06 09:55:58.726 renniksoft[4727:707] FREEMEM: 262705152
2011-06-06 09:55:59.242 renniksoft[4727:707] FREEMEM: 262852608
2011-06-06 09:55:59.737 renniksoft[4727:707] FREEMEM: 262389760
2011-06-06 09:56:00.243 renniksoft[4727:707] FREEMEM: 261931008
2011-06-06 09:56:00.751 renniksoft[4727:707] FREEMEM: 261992448
2011-06-06 09:56:01.280 renniksoft[4727:707] FREEMEM: 261574656
2011-06-06 09:56:01.774 renniksoft[4727:707] FREEMEM: 261148672
2011-06-06 09:56:02.290 renniksoft[4727:707] FREEMEM: 260755456
2011-06-06 09:56:02.820 renniksoft[4727:707] FREEMEM: 260837376
2011-06-06 09:56:03.334 renniksoft[4727:707] FREEMEM: 260395008
2011-06-06 09:56:03.825 renniksoft[4727:707] FREEMEM: 259932160
2011-06-06 09:56:04.346 renniksoft[4727:707] FINAL FREEMEM: 259555328
The amount of free memory reduces each time round the loop in proportion to the managed objects I fetch e.g. if I fetch twice as many objects then the free memory reduces twice as quickly – so I’m pretty confident it is the managed objects that are not being released.
Note that the entities that are being fetched are very basic, just two attributes, a string and a 16 bit integer. There are 1000 of them being fetched in the examples above. The code I used to generate them is as follows:
// Create test entities
for(int i=0; i<1000; i++) {
id entity = [NSEntityDescription insertNewObjectForEntityForName:@"TestEntity" inManagedObjectContext:context];
[entity setValue:[NSString stringWithFormat:@"%d",i] forKey:@"name"];
[entity setValue:[NSNumber numberWithInt:i] forKey:@"value"];
}
if (![context save:nil]) {
NSLog(@"Couldn't save");
}
If anyone can explain to me what is going on I’d be very grateful! This issue is the only only one holding up the release of my app. It works beautifully on the simulator!!
Please let me know if there’s any more info I can supply.
Doh! Here’s the point where I look dumb!
I had ‘NSZombieEnabled’ set to YES which meant that the fetched data wasn’t getting released! It’s all working fine without that 🙂