Re: [libvirt] [libvirt-python PATCH 03/23] remove useless check for NULL before Py_XDECREF
On 09/29/2015 10:29 AM, Pavel Hrdina wrote:
On Sat, Sep 26, 2015 at 09:08:35AM -0400, John Ferlan wrote:
>
>
> On 09/24/2015 10:01 AM, Pavel Hrdina wrote:
>> Signed-off-by: Pavel Hrdina <phrdina(a)redhat.com>
>> ---
>> libvirt-override.c | 9 +++------
>> 1 file changed, 3 insertions(+), 6 deletions(-)
>>
>> diff --git a/libvirt-override.c b/libvirt-override.c
>> index 14aa0e9..114104b 100644
>> --- a/libvirt-override.c
>> +++ b/libvirt-override.c
>> @@ -2303,12 +2303,9 @@ libvirt_virRegisterErrorHandler(ATTRIBUTE_UNUSED PyObject
* self,
>> pyobj_f);
>>
>> virSetErrorFunc(NULL, libvirt_virErrorFuncHandler);
>> - if (libvirt_virPythonErrorFuncHandler != NULL) {
>> - Py_XDECREF(libvirt_virPythonErrorFuncHandler);
>> - }
>> - if (libvirt_virPythonErrorFuncCtxt != NULL) {
>> - Py_XDECREF(libvirt_virPythonErrorFuncCtxt);
>> - }
>> +
>> + Py_XDECREF(libvirt_virPythonErrorFuncHandler);
>> + Py_XDECREF(libvirt_virPythonErrorFuncCtxt);
>
> I keep looking at this and thinking why? Why was it added and what is
> it protecting. Looking at libvirt_virErrorFuncHandler it seems only
> libvirt_virPythonErrorFuncCtxt gets the Py_XINCREF and that's based on
> whether libvirt_virPythonErrorFuncHandler is NULL or not.
I don't understand what do you mean by this??
I guess the whole Py_XDECREF usage is still a bit of a mystery. I
believe I was trying to consider why someone would have checked for NULL
previously. I know from checking it was written that way. But I assume
now that if on input it was NULL then nothing happens.
No issues otherwise -
John
>
> Just feels like something subtle is going on. Also it's a register
> handler and we're decrementing something that never got incremented.
Check the whole function. It will decrement the old handlers, check for
existence of new handlers and clean/set new handlers. And before setting the
new handlers, we need to increment them, otherwise they will be cleared by GC.
Everything that is parsed by 'PyArg_ParseTuple' has to be incremented, if you
need to use those object outside of the function scope, where you've called that
parser.
Pavel
>
> John
>>
>> if ((pyobj_f == Py_None) && (pyobj_ctx == Py_None)) {
>> libvirt_virPythonErrorFuncHandler = NULL;
>>