[PATCH 2/2] kernel32: conditional variable support

[Marcus Meissner]

On Sun, Dec 30, 2012 at 12:02:34AM +0400, Nikolay Sivov wrote:
> On 12/29/2012 23:04, Marcus Meissner wrote:
> >From: Marcus Meissner <marcus at jet.(none)>
> >
> >Modeled pretty much after the implementation described
> >in glibc/nptl/DESIGN-condvar.txt with its futex usage
> >sofar replaced by regular Win32 Semaphores.
> >
> >An additional futex implementation is possible.
> >
> >I *think* I have the semantics correct, there is 1 small
> >place where it might have unnecessary CPU usage though.
> >
> >Ciao, Marcus
> 
> >+/**********************************************************************
> >+ *           InitializeConditionVariable     (KERNEL32.@)
> >+ */
> >+VOID WINAPI InitializeConditionVariable(PCONDITION_VARIABLE variable)
> >+{
> >+    struct _condition_var_intern *var;
> >+    variable->Ptr = HeapAlloc(GetProcessHeap(),HEAP_ZERO_MEMORY,sizeof(struct _condition_var_intern));
> >+    var = variable->Ptr;
> >+    if (!var) return;
> >+    InitializeCriticalSection (&var->crit);
> >+    var->crit.DebugInfo->Spare[0] = (DWORD_PTR)(__FILE__ ": ConditionVariable.cs");
> >+}
> I don't think it allocates anything at all, what makes me believe
> that is that stuff like CONDITION_VARIABLE_INIT exists.
> After googling a bit for it I see that gallium from mesa has some
> platform dependent stuff in code that uses this API like that:
> 
> ---
> +#define pipe_static_condvar(cond) \
>  + /*static*/ pipe_condvar cond = CONDITION_VARIABLE_INIT
> ---
> 
> So this structure has nothing more than a single pointer value,
> value 0 of it means it's initialized. I think you could just add
> some tests to see if it's really reset to 0 from initial value.

I am not fully sure. The SDK only has "PVOID Ptr" and that alone
is not enough space to implement conditional variables.

CONDITION_VARIABLE_INIT is only there to init it to NULL.
(if you look at the SDK CONDITION_VARIABLE_INIT seems to be {0} )

So I suspect some private data structure is hidden into it.

I however do not know if windows allocates it from heap
or from where exactly.
 
> Also regarding tests I don't think randomizing timeouts is a good
> idea cause it adds some unpredictable behaviour and it's not really
> clear if we could rely on such tests results.

I have to think about those some more :/

I testing Adobe Lightroom 4 with the patch I encountered more conditions
I should probably also test for.

Ciao, Marcus