(timeout in ms vs. XSyncValueSubtract) Frozen client, found cause, need advise for fix

[walter harms]

Am 21.02.2017 20:28, schrieb Mihail Konev:
> On Tue, Feb 21, 2017 at 05:48:19PM +0100, walter harms wrote:
>>>
>> 	
>> XSyncValueSubtract is doing as expected,
>> XSyncValue is the simulation of 64bitvalues on 32bit.
>> see this in hex:
>>  100000001
>> -000000002
>>  0FFFFFFFF = 4294967295 in .lo
>>
> 
> Kind of - it errorneously returns
> 
>  1 0000 0001
> -0 0000 0002
>  1 ffff ffff
> 
> Test source attached.
> 
> I.e.
>   XSyncValueSubtract should handle the .lo becoming <0,
>   and it checks only for .lo_after_subtract < .lo,
>   which would only be aplicable to uint.
> 
> E.g. there is a typo in XSyncValue.lo definition - it should be uint
> instead.
> Also in ServertimeBlockHandler, "timeout" is unsigned,
> while it is get from signed .lo and used as signed arg to
> AdjustWaitForTimeout.


yep, i noticed that "int t = (a).lo;" and was confused. But the experiments showed
is seems to work.

#define _XSyncValueSubtract(presult,a,b,poverflow) {\
        int t = (a).lo;\
        Bool signa = XSyncValueIsNegative(a);\
        Bool signb = XSyncValueIsNegative(b);\
        ((presult)->lo = (a).lo - (b).lo);\
        ((presult)->hi = (a).hi - (b).hi);\
        if (t>(presult)->lo) (presult)->hi--;\
        *poverflow = ((signa == signb) && !(signa == XSyncValueIsNegative(*presu
lt)));\
     }


my test code:

#include <stdio.h>
#include <X11/Xlibint.h>
#include <X11/extensions/sync.h>

// gcc xsync.c -lXext
int main()
{
        XSyncValue a,b,c;
        XSyncValue result;
        Bool ov;


        XSyncIntToValue(&a, 100);
        XSyncIntToValue(&b, 200);

        XSyncValueSubtract(&result, b, a, &ov);
        printf("result.hi = %d, result.lo = %d, overflow = %d\n", result.hi, result.lo, ov);
}

I did not look at the asm level but the interessting question is:
can that be replace by int64_t ? is it done somewhere else ?

re,
 wh

> 
> Perhaps also:
>   AdjustWaitForTimeout should not be used if overflow != 0
>   Because something is wrong then as (pnext_time < Now) ?
> 
> Mihail