GC being too eager?

[Paulo Pinto]

On Thursday, 10 April 2014 at 09:31:30 UTC, John Colvin wrote:
> On Thursday, 10 April 2014 at 09:24:51 UTC, Paulo Pinto wrote:
>> In a toy project I am working on with D v2.065, I came to the 
>> following situation:
>>
>> Node path = solver.find (map, start, end);
>> if (path !is null) {
>>    path.writeContents();  <-- Access Violation
>> }
>>
>> Apparently between the test and trying to use the class, the 
>> reference becomes null.
>>
>> Quite strange in a single threaded application.
>>
>> Any idea what might be happening or should I delve into 
>> assembly?
>>
>> --
>> Paulo
>
> Delve delve delve. Is this in an optimised build?

Well, I got into something but it will require more research.

The above code is


0x0040223a e8ed360100       call        solver.find (0041592c)
0x0040223f 8945f0           mov         dword ptr [path],eax
0x00402242 83c40c           add         esp,0c
0x00402245 85c0             test        eax,eax
0x00402247 7408             je          D main+00000241 (00402251)
0x00402249 8b45f0           mov         eax,dword ptr [path]
0x0040224c 8b08             mov         ecx,dword ptr [eax]
0x0040224e ff5138           call        dword ptr [ecx+38]
0x00402251 ff3564e14400     push        dword ptr 
[__xt_z+000000f4 (0044e164)]
0x00402257 ff3560e14400     push        dword ptr 
[__xt_z+000000f0 (0044e160)]
0x0040225d 837df000         cmp         dword ptr [path],00
0x00402261 0f95c0           setne       al
0x00402264 e86b8d0000       call        
std.stdio.writefln!(string, bool).writefln (0040afd4)

After find() gets called, eax = 0x0030f900 which points to 
nowhere valid.

Hence, ecx will contain a null address and [ecx + 38] as vtable 
lookup points to 0x00000038, which lands in no man's land and 
boom.

Trying to get deep into this will require a bit more time.

I wonder if this is caused by the nodes being stored into a 
BinaryHeap with an Array store, coupled with a RedBlackTree as 
well. Maybe some interaction between the manual memory management 
and the GC.

More info later on.

--
Paulo