Closing events and releasing resources in notify function

Closing events and releasing resources in notify function

[Arka Sharma]

Hi,

Is it ok to close the event and release the resource allocated to be
sent as context inside the notify function. May be something like this

VOID
EFIAPI
NotifyRoutine (
       EFI_EVENT Event,
       VOID  *Context
)
{
   //
   // Perform intended task
   //
   FreePool (Context);
   gBS->CloseEvent (Event);
}

In the above example Context was allocated before creating the event
and passed as a parameter to CreateEvent().

Regards,
Arka

Re: Closing events and releasing resources in notify function

[Andrew Fish]

> On Mar 23, 2017, at 11:22 PM, Arka Sharma <arka.sw1988@gmail.com> wrote:
> 
> Hi,
> 
> Is it ok to close the event and release the resource allocated to be
> sent as context inside the notify function. May be something like this
> 
> VOID
> EFIAPI
> NotifyRoutine (
>       EFI_EVENT Event,
>       VOID  *Context
> )
> {
>   //
>   // Perform intended task
>   //
>   FreePool (Context);
>   gBS->CloseEvent (Event);

You should close the event before you free the context, or you will have a race. You need to make sure there is no way for EFI to signal the event before you free the context. 

This all assumes you don't have other code doing crazy stuff with the Context or Event. It would  be a different answer for CreateEventEx()

Thanks,

Andrew Fish

> }
> 
> In the above example Context was allocated before creating the event
> and passed as a parameter to CreateEvent().
> 
> Regards,
> Arka
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel

Re: Closing events and releasing resources in notify function

[Arka Sharma]

Thanks Andrew for your reply. In this case I am creating the event
with CreateEvent() and not with CreateEventEx(). I am attempting to
free the Context inside the notify function which will be called after
Event is signaled, and Context is only accessed before CreateEvent()
and inside the NotifyRoutine(). So the change you are suggesting is
inside the notify function I should call CloseEvent() first before
freeing Context right ?

On Fri, Mar 24, 2017 at 12:07 PM, Andrew Fish <afish@apple.com> wrote:
>
>> On Mar 23, 2017, at 11:22 PM, Arka Sharma <arka.sw1988@gmail.com> wrote:
>>
>> Hi,
>>
>> Is it ok to close the event and release the resource allocated to be
>> sent as context inside the notify function. May be something like this
>>
>> VOID
>> EFIAPI
>> NotifyRoutine (
>>       EFI_EVENT Event,
>>       VOID  *Context
>> )
>> {
>>   //
>>   // Perform intended task
>>   //
>>   FreePool (Context);
>>   gBS->CloseEvent (Event);
>
> You should close the event before you free the context, or you will have a race. You need to make sure there is no way for EFI to signal the event before you free the context.
>
> This all assumes you don't have other code doing crazy stuff with the Context or Event. It would  be a different answer for CreateEventEx()
>
> Thanks,
>
> Andrew Fish
>
>> }
>>
>> In the above example Context was allocated before creating the event
>> and passed as a parameter to CreateEvent().
>>
>> Regards,
>> Arka
>> _______________________________________________
>> edk2-devel mailing list
>> edk2-devel@lists.01.org
>> https://lists.01.org/mailman/listinfo/edk2-devel
>

Re: Closing events and releasing resources in notify function

[Andrew Fish]

> On Mar 24, 2017, at 12:07 AM, Arka Sharma <arka.sw1988@gmail.com> wrote:
> 
> Thanks Andrew for your reply. In this case I am creating the event
> with CreateEvent() and not with CreateEventEx(). I am attempting to
> free the Context inside the notify function which will be called after
> Event is signaled, and Context is only accessed before CreateEvent()
> and inside the NotifyRoutine(). So the change you are suggesting is
> inside the notify function I should call CloseEvent() first before
> freeing Context right ?
> 

Yes as your event can get signaled until you close it in the general case. 

Thanks,

Andrew Fish

> On Fri, Mar 24, 2017 at 12:07 PM, Andrew Fish <afish@apple.com> wrote:
>> 
>>> On Mar 23, 2017, at 11:22 PM, Arka Sharma <arka.sw1988@gmail.com> wrote:
>>> 
>>> Hi,
>>> 
>>> Is it ok to close the event and release the resource allocated to be
>>> sent as context inside the notify function. May be something like this
>>> 
>>> VOID
>>> EFIAPI
>>> NotifyRoutine (
>>>      EFI_EVENT Event,
>>>      VOID  *Context
>>> )
>>> {
>>>  //
>>>  // Perform intended task
>>>  //
>>>  FreePool (Context);
>>>  gBS->CloseEvent (Event);
>> 
>> You should close the event before you free the context, or you will have a race. You need to make sure there is no way for EFI to signal the event before you free the context.
>> 
>> This all assumes you don't have other code doing crazy stuff with the Context or Event. It would  be a different answer for CreateEventEx()
>> 
>> Thanks,
>> 
>> Andrew Fish
>> 
>>> }
>>> 
>>> In the above example Context was allocated before creating the event
>>> and passed as a parameter to CreateEvent().
>>> 
>>> Regards,
>>> Arka
>>> _______________________________________________
>>> edk2-devel mailing list
>>> edk2-devel@lists.01.org
>>> https://lists.01.org/mailman/listinfo/edk2-devel
>>