Swizzle retain/release/autorelease to debug busted reference counting

swizzle-retain-release-autorelease

// Use with https://github.com/rentzsch/jrswizzle
// MIT license
// After your program dies because with a zombie, examine [theBigLog objectForKey:@"0x12345"], subbing the address of the thing that died. You can get stack traces referred to in the logs by looking up the "stack-12345" numbers in the same dict. To track a particular object, add [NSValue valueWithPointer:myobject] to debugList in a @synchronized block.

@interface ClassToDebug : NSColor
@end

@interface ClassToDebug (DebugRefs)
@end

static NSMutableSet *debugList;
NSMutableDictionary *theBigLog;

@implementation ClassToDebug (DebugRefs)
- (bool)shouldDebugRefs {
    @synchronized([NSObject class]) {
        return [debugList containsObject:[NSValue valueWithPointer:self]];
    }
}
- (void)logDebugRefs:(NSString *)msg {
    @synchronized([NSObject class]) {
        NSString *key = [NSString stringWithFormat:@"%p", self];
        NSMutableString *s = [theBigLog objectForKey:key];
        if (!s) {
            s = [[NSMutableString alloc] init];
            [theBigLog setObject:s forKey:key];
        }
        [s appendString:msg];
    }
}

- (NSString *)debugCallStack {
    NSString *syms = [[NSThread callStackSymbols] description];
    NSUInteger hash = [syms hash];
    NSString *key = [NSString stringWithFormat:@"stack-%llu", hash];
    @synchronized([NSObject class]) {
        if (![theBigLog objectForKey:key]) {
            [theBigLog setObject:syms forKey:key];
        }
    }
    return key;
}

- (id)debugRefsRetain {
    id rv = [self debugRefsRetain];
    if ([self shouldDebugRefs]) {
        [self logDebugRefs:[NSString stringWithFormat:@"Retain %@ from %@ sending rc to %d\n", self, [self debugCallStack], (int)[self retainCount]]];
    }
    return rv;
}

- (oneway void)debugRefsRelease {
    if ([self shouldDebugRefs]) {
        [self logDebugRefs:[NSString stringWithFormat:@"Release %@ from %@ sending rc to %d\n", self, [self debugCallStack], (int)[self retainCount]-1]];
        if ([self retainCount] == 1) {
            @synchronized([NSObject class]) {
                [debugList removeObject:[NSValue valueWithPointer:self]];
            }
        }
    }
    [self debugRefsRelease];
}

- (id)debugRefsAutorelease {
    id rv = [self debugRefsAutorelease];
    if ([self shouldDebugRefs]) {
        [self logDebugRefs:[NSString stringWithFormat:@"Autorelease %@ from %@ sending rc to %d\n", self, [self debugCallStack], (int)[self retainCount]]];
    }
    return rv;
}


@end

void DoSwizzle() {
    debugList = [[NSMutableSet alloc] init];
    theBigLog = [[NSMutableDictionary alloc] init];
    NSError *e = nil;
    [ClassToDebug jr_swizzleMethod:@selector(retain) withMethod:@selector(debugRefsRetain) error:&e];
    assert(!e);
    [ClassToDebug jr_swizzleMethod:@selector(release) withMethod:@selector(debugRefsRelease) error:&e];
    assert(!e);
    [ClassToDebug jr_swizzleMethod:@selector(autorelease) withMethod:@selector(debugRefsAutorelease) error:&e];
    assert(!e);
}