Bug 167848 – Static Analyzer: JSContext.mm: Incorrect decrement of the reference count of an object

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Joseph Pecoraro]

Static Analyzer: JSContext.mm: Incorrect decrement of the reference count of an object 

> Source/JavaScriptCore/API/JSContext.mm:87:5: warning: Incorrect decrement of the reference count of an object that is not owned at this point by the caller
>     [self.exceptionHandler release];
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 1 warning generated.

In practice this is normally harmless, but lets do the canonical thing here and just release the ivar instead of going through the getter.

[Joseph Pecoraro]

Created attachment 300652 [details]
[PATCH] Proposed Fix

[Saam Barati]

Comment on attachment 300652 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=300652&action=review

> Source/JavaScriptCore/API/JSContext.mm:-50
> -@synthesize exceptionHandler;

Is this auto generated?

> Source/JavaScriptCore/API/JSContext.mm:85
> +    [_exceptionHandler release];

Is this because the copy semantics of the getter?

[Joseph Pecoraro]

Comment on attachment 300652 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=300652&action=review

>> Source/JavaScriptCore/API/JSContext.mm:-50
>> -@synthesize exceptionHandler;
> 
> Is this auto generated?

Yes, and the auto-generated version would be equivalent to:

    @synthesize exceptionHandler = _exceptionHandler;

>> Source/JavaScriptCore/API/JSContext.mm:85
>> +    [_exceptionHandler release];
> 
> Is this because the copy semantics of the getter?

The idea here is that we just release our ivar directly instead of accessing it through the getter (which typically implies a memory neutral operation). The getter could even be overridden by a subclass that returns something else that isn't owned by this class, so invoking release would be incorrect. We don't own the value returned by the getter, but we own the ivar.

[WebKit Commit Bot]

Comment on attachment 300652 [details]
[PATCH] Proposed Fix

Clearing flags on attachment: 300652

Committed r211740: <http://trac.webkit.org/changeset/211740>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.