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Re: [libvirt] [PATCH v4 RESEND 1/4] threadpool impl



On 12/02/2010 05:28 AM, Daniel P. Berrange wrote:
>> +virThreadPoolPtr virThreadPoolNew(size_t minWorkers,
>> +                                  size_t maxWorkers,
>> +                                  virThreadPoolJobFunc func,
>> +                                  void *opaque) ATTRIBUTE_NONNULL(3)
>> +                                                ATTRIBUTE_RETURN_CHECK;
> 
> ATTRIBUTE_RETURN_CHECK doesn't serve any useful purpose
> when placed on constructors, since the caller will always
> "use" the return value by assigning the pointer to some
> variable. The compiler can thus never detect whether you
> check for null or not, even with this annotation.

Good point.  However, in looking through gcc's documentation, maybe it's
time we introduce a new attribute for constructors:

#define ATTRIBUTE_MALLOC __attribute__((__malloc__))

     The `malloc' attribute is used to tell the compiler that a function
     may be treated as if any non-`NULL' pointer it returns cannot
     alias any other pointer valid when the function returns.  This
     will often improve optimization.  Standard functions with this
     property include `malloc' and `calloc'.  `realloc'-like functions
     have this property as long as the old pointer is never referred to
     (including comparing it to the new pointer) after the function
     returns a non-`NULL' value.

I think that tools like clang might also be able to feed off of the
malloc attribute to make decisions about whether NULL-checking needs to
be performed on the result, and/or provide better leak detection analysis.

However, that's a separate idea, and doesn't affect this series.

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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