Re: Passing param by reference then using within block throws exception

[Steve Mills]

On Sep 22, 2016, at 02:45 PM, "Gary L. Wade"  
wrote:

Look at these two lines:

   __block NSString* noFillMeIn;
...
         *noFillMeIn = @"wow";

Unless the original code is correct, you've got mismatched pointers, and you 
should try turning on more warnings and reading what they say, as well as 
trying the analyzer.

Copy & paste mistake. The quoted syntax won't even compile.

Sent from iCloud's ridiculous UI, so, sorry about the formatting

 
___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Re: Passing param by reference then using within block throws exception

[Steve Mills]

On Sep 22, 2016, at 02:31 PM, Kyle Sluder  wrote:

Are you able to reproduce this in a sample app? I tried the following
but got no crash:

I haven't tried. The real method this came from is much more complex than my 
simplified example; 6 enumerate* loop blocks on dicts and arrays (a couple 
nested), another parameter before the reference parameter, lots of object 
allocation. After spending the bulk of my day on tracking down the problem, I 
don't want to waste more trying to come up with a sample that duplicates it. 
I'm sure you understand. If ARC can't do the right thing, it should be flagged 
as something that the user should change.

Sent from iCloud's ridiculous UI, so, sorry about the formatting

 
___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Passing param by reference then using within block throws exception

[Gary L. Wade]

Look at these two lines:

>__block NSString* noFillMeIn;
...
>  *noFillMeIn = @"wow";


Unless the original code is correct, you've got mismatched pointers, and you 
should try turning on more warnings and reading what they say, as well as 
trying the analyzer.
--
Gary L. Wade (Sent from my iPhone)
http://www.garywade.com/

> On Sep 20, 2016, at 2:06 PM, Steve Mills  wrote:
> 
> I'm turning on ARC for a project (yay) and have run into a problem I can't 
> wrap my head around. It always worked fine before ARC. When I turn zombies 
> on, doing "memory history 0x610004279ac0" can't find it in the history. 
> Here's the method and the call to it:
> 
> -(void) doStuff:(NSString**)fillMeIn
> {
>[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL* stop) {
>   if(obj.flag) {
>  *stop = YES;
>  *fillMeIn = @"wow";
>   }
>}];
> }
> 
> NSString* getFilledIn;
> 
> [thing doStuff:];
> 
> The call to doStuff: results in EXC_BAD_ACCESS, or "*** -[CFString retain]: 
> message sent to deallocated instance 0x610004279ac0" if I turn zombies on.
> 
> I tried changing the param type to (NSString** _Nonnull), thinking it was 
> confused about my knowing that the reference will never be nil, but it didn't 
> help. Then I got to thinking about the reference being assigned inside the 
> block and changed it to:
> 
> -(void) doStuff:(NSString** _Nonnull)fillMeIn
> {
>__block NSString* noFillMeIn;
>
>[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL* stop) {
>   if(obj.flag) {
>  *stop = YES;
>  *noFillMeIn = @"wow";
>   }
>}];
>
>*fillMeIn = noFillMeIn;
> }
> 
> That seems to fix it. Is there a better way to deref and assign to the param 
> from within the block?
> 
> Sent from iCloud's ridiculous UI, so, sorry about the formatting
___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Re: Passing param by reference then using within block throws exception

[Kyle Sluder]

On Wed, Sep 21, 2016, at 09:22 AM, Steve Mills wrote:
> On Sep 21, 2016, at 08:53 AM, Alex Zavatone  wrote:
> 
> Stab in the dark here, but I'm stabbing blank. Is there an Instruments
> tool or debugging option to detect this? 
> 
> Thanks for getting stabby. Fourvel appreciates it (only relevant if
> you're a CBB fan). It doesn't appear that anything will detect this. When
> zombies is on, it says an address is attempting to be retained but was
> previously released. That's a bit of a red herring, since the only 2
> variables being uses have just been declared and initialized right before
> the call to the method. If anything, the process of converting to ARC or
> the static analyzer should've flagged this as a problem.

Are you able to reproduce this in a sample app? I tried the following
but got no crash:

#include 
#import 

static void foo(NSString **fillMeIn) {
[@[@"a"] enumerateObjectsUsingBlock:^(id obj, NSUInteger idx,
BOOL *stop) {
*fillMeIn = obj;
*stop = YES;
}];
}

int main(int argc, char **argv) {
@autoreleasepool {
NSString *out;
foo();
printf("%s", out.UTF8String);
}
return 0;
}


--Kyle
___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Passing param by reference then using within block throws exception

[Steve Mills]

On Sep 21, 2016, at 08:53 AM, Alex Zavatone  wrote:

Stab in the dark here, but I'm stabbing blank. Is there an Instruments tool or debugging option to detect this? 


Thanks for getting stabby. Fourvel appreciates it (only relevant if you're a 
CBB fan). It doesn't appear that anything will detect this. When zombies is on, 
it says an address is attempting to be retained but was previously released. 
That's a bit of a red herring, since the only 2 variables being uses have just 
been declared and initialized right before the call to the method. If anything, 
the process of converting to ARC or the static analyzer should've flagged this 
as a problem.

Sent from iCloud's ridiculous UI, so, sorry about the formatting

 
___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Passing param by reference then using within block throws exception

[Alex Zavatone]

Stab in the dark here, but I'm stabbing blank.  Is there an Instruments tool or 
debugging option to detect this?  

On Sep 21, 2016, at 7:53 AM, Steve Mills wrote:

> On Sep 21, 2016, at 01:29:37, Jens Alfke  wrote:
>> 
>> I think the real problem is that the -enumerateObjectsUsingBlock: method has 
>> an autorelease pool. If your real code is assigning something other than a 
>> string constant to *fillMeIn, that string will probably get dealloced when 
>> the autorelease pool drains. Your workaround is correct, since assigning the 
>> string to noFillMeIn causes it to be retained.
> 
> Perhaps, but that couldn't be the cause of the crash. I might not have been 
> totally clear, but the crash happens while setting up to call the method, not 
> inside the method or after it returns.
> 
> --
> Steve Mills
> Drummer, Mac geek
> 
> 
> ___
> 
> Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
> 
> Please do not post admin requests or moderator comments to the list.
> Contact the moderators at cocoa-dev-admins(at)lists.apple.com
> 
> Help/Unsubscribe/Update your Subscription:
> https://lists.apple.com/mailman/options/cocoa-dev/zav%40mac.com
> 
> This email sent to z...@mac.com


___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Passing param by reference then using within block throws exception

[Steve Mills]

On Sep 21, 2016, at 01:29:37, Jens Alfke  wrote:
> 
> I think the real problem is that the -enumerateObjectsUsingBlock: method has 
> an autorelease pool. If your real code is assigning something other than a 
> string constant to *fillMeIn, that string will probably get dealloced when 
> the autorelease pool drains. Your workaround is correct, since assigning the 
> string to noFillMeIn causes it to be retained.

Perhaps, but that couldn't be the cause of the crash. I might not have been 
totally clear, but the crash happens while setting up to call the method, not 
inside the method or after it returns.

--
Steve Mills
Drummer, Mac geek


___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Passing param by reference then using within block throws exception

[Jens Alfke]

I think the real problem is that the -enumerateObjectsUsingBlock: method has an 
autorelease pool. If your real code is assigning something other than a string 
constant to *fillMeIn, that string will probably get dealloced when the 
autorelease pool drains. Your workaround is correct, since assigning the string 
to noFillMeIn causes it to be retained.

—Jens
___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Passing param by reference then using within block throws exception

[Doug Hill]

I think this is the exact solution. As I'm sure you've tried, you can't use the 
__block modifier on method parameters, as you will get the following compiler 
error:

__block attribute not allowed, only allowed on local variables

So, you're doing the right thing creating the local as a temporary to 
eventually assign to the method parameter.

Doug Hill



> On Sep 20, 2016, at 2:06 PM, Steve Mills  wrote:
> 
> I'm turning on ARC for a project (yay) and have run into a problem I can't 
> wrap my head around. It always worked fine before ARC. When I turn zombies 
> on, doing "memory history 0x610004279ac0" can't find it in the history. 
> Here's the method and the call to it:
> 
> -(void) doStuff:(NSString**)fillMeIn
> {
>[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL* stop) {
>   if(obj.flag) {
>  *stop = YES;
>  *fillMeIn = @"wow";
>   }
>}];
> }
> 
> NSString* getFilledIn;
> 
> [thing doStuff:];
> 
> The call to doStuff: results in EXC_BAD_ACCESS, or "*** -[CFString retain]: 
> message sent to deallocated instance 0x610004279ac0" if I turn zombies on.
> 
> I tried changing the param type to (NSString** _Nonnull), thinking it was 
> confused about my knowing that the reference will never be nil, but it didn't 
> help. Then I got to thinking about the reference being assigned inside the 
> block and changed it to:
> 
> -(void) doStuff:(NSString** _Nonnull)fillMeIn
> {
>__block NSString* noFillMeIn;
>
>[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL* stop) {
>   if(obj.flag) {
>  *stop = YES;
>  *noFillMeIn = @"wow";
>   }
>}];
>
>*fillMeIn = noFillMeIn;
> }
> 
> That seems to fix it. Is there a better way to deref and assign to the param 
> from within the block?


___

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to arch...@mail-archive.com