endless "for" loop in release configuration of iPhone app - iphone

Question

i have the following code in my application:
NSArray *lstAttributes = [conditionAttribute componentsSeparatedByString:cstrSystemUIConfigurationAttributeConditionSeparator],
*lstValues = [conditionValue componentsSeparatedByString:cstrSystemUIConfigurationAttributeConditionSeparator],
*lstValueTypes = [conditionValueType componentsSeparatedByString:cstrSystemUIConfigurationAttributeConditionSeparator];
if([lstAttributes count] != [lstValues count] ||
[lstAttributes count] != [lstValueTypes count]) return NO;
BOOL bResult = YES;
NSLog(#"attributes amount - %u", [lstAttributes count]);
for(uint i = 0; i < [lstAttributes count]; i ++)
{
NSLog(#"counter: %u", i);
SystemUIConfigurationAttributeCondition *condition = [SystemUIConfigurationAttributeCondition new];
condition.conditionAttribute = [lstAttributes objectAtIndex:i];
condition.conditionValue = [lstValues objectAtIndex:i];
condition.conditionValueType = [lstValueTypes objectAtIndex:i];
bResult &= [self checkCondition:condition forOwner:owner];
FreeObject(&condition);
if(!bResult) break;
}
return bResult;
everything is fine in "debug" configuration. but once i switch it to "release" i face the endless loop. console shows me the following: attributes amount - 2, counter: 0, counter: 1, counter: 1, counter: 1, counter: 1, counter: 1, counter: 1, ...... etc.
i tried to use different "for" and "while" operators, but nothing of that worked correctly. the loop still can't be stopped.
has anyone faced the same problem before?

Answer 1

Since you mention in your comments that it works if you comment out the &= operation, I'd change that line to:
bResult = bResult && [self checkCondition:condition forOwner:owner];
This does a boolean AND, which is what you really intend to do on this line anyway. &= does a bitwise AND, which isn't always equivalent to a boolean AND, since any nonzero value evaluates to true. For example:
BOOL a = 1;
BOOL b = 2;
if (a && b) {
NSLog (#"a && b is true"); // This line will execute
}
if (a & b) {
NSLog (#"a & b is true"); // This line won't execute
}
Since it's common to use object addresses in our conditionals, using the bitwise AND in place of a boolean AND could create bugs. For example, if you return an object address from getCondition:fromOwner:, intending it to mean YES, and that memory address happens to be an even number, then a bitwise AND with YES will evaluate to NO, where a boolean AND would evaluate to YES.
My best guess as to the cause of your specific bug is that the bitwise-AND is somehow causing a buffer overrun, which stomps on your i variable. If that hypothesis is correct, then switching to a boolean AND should fix that too.

Answer 2

workaround for this bug as promised:
at first i tried to use code blocks to enumerate all objects in a list instead of "for" loop.
__block BOOL bResult = YES;
[lstAttributes enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
{
SystemUIConfigurationAttributeCondition *condition = [SystemUIConfigurationAttributeCondition new];
condition.conditionAttribute = [lstAttributes objectAtIndex:idx];
condition.conditionValue = [lstValues objectAtIndex:idx];
condition.conditionValueType = [lstValueTypes objectAtIndex:idx];
bResult &= [self checkCondition:condition forOwner:owner];
FreeObject(&condition);
if(!bResult) *stop = YES;
}];
but i got a crash on second iteration. "lstValues" and "lstValueTypes" pointers suddenly changed their values and application received EXC_BAD_ACCESS. possibly usage of 3 arrays while enumerating only 1 of them is not a good idea. debugger shows that enumeration is performed on the same thread, but 2 of 3 arrays are corrupted by the moment of 2nd iteration.
so i decided to split up my initial loop into 2 parts:
prepare a list of conditions
check each condition.
first is a usual "for" loop, second - 'enumerateObjectsUsingBlock:" method of NSArray class. so the final code looks like:
NSArray *lstAttributes = [conditionAttribute componentsSeparatedByString:cstrSystemUIConfigurationAttributeConditionSeparator],
*lstValues = [conditionValue componentsSeparatedByString:cstrSystemUIConfigurationAttributeConditionSeparator],
*lstValueTypes = [conditionValueType componentsSeparatedByString:cstrSystemUIConfigurationAttributeConditionSeparator];
if([lstAttributes count] != [lstValues count] ||
[lstAttributes count] != [lstValueTypes count]) return NO;
NSMutableArray *lstConditions = [NSMutableArray new];
for(uint i = 0; i < [lstAttributes count]; i ++)
{
SystemUIConfigurationAttributeCondition *condition = [SystemUIConfigurationAttributeCondition new];
condition.conditionAttribute = [lstAttributes objectAtIndex:i];
condition.conditionValue = [lstValues objectAtIndex:i];
condition.conditionValueType = [lstValueTypes objectAtIndex:i];
[lstConditions addObject:condition];
FreeObject(&condition);
}
__block BOOL bResult = YES;
[lstConditions enumerateObjectsUsingBlock:^(id obj, NSUInteger i, BOOL *stop)
{
if([self checkCondition:[lstConditions objectAtIndex:i] forOwner:owner] == NO)
{
bResult = NO;
*stop = YES;
}
}];
FreeObject(&lstConditions);
return bResult;
this code works.
i would appreciate if anyone can explain the behavior of my initial loop.