Yet another strike against the current AA implementation

[Sean Kelly]

Andrei Alexandrescu wrote:
> Georg Wrede wrote:
>> Andrei Alexandrescu wrote:
>>> Computing the stack depth even for non-recursive functions is an 
>>> interprocedural analysis so it's difficult to do modularly. The stack 
>>> is also unchecked so going with a "good enough" approximation is 
>>> bound to be risky.
>>
>> The old size estimation problem. No matter how big you decide on, 
>> somewhere is an idiot who will blow that size too.
>>
>>
>> A runtime solution just occurred to me. The newly allocated stack for 
>> a thread is zeroed first, right? Well then, just before the thread 
>> finishes, one could scan the stack area, and find the first address 
>> that contains a non-zero value.
>>
>> This isn't bullet proof in theory, but hey, the aim is to help in 
>> /estimating/ the needed stack size.

You could have the GC report stack sizes when it performs a collection. 
  No guarantee it would be a high-water mark, but it's something.

>> Incidentally, this raises another thought: what if the stack was 
>> extendable? Like D arrays? A stack overflow would trigger a relocation 
>> of the stack, and then continue. Being able to have hundreds of small 
>> stacks would be useful in other things than threads, too.
> 
> That would be great. I don't know whether it can be done.

Windows works this way, and it's possible to do in user code (the Fiber 
implementation has some of the groundwork for this).  Beyond "usable" 
stack is a guard page that triggers a stack extension when hit.  But I 
think if you grow the stack past the guard page without ever touching it 
you can still blow the stack.

> By the way, I think you're underestimating how much stack the OS gives 
> to the stack. On my system:
> 
> $ grep PTHREAD_STACK /usr/include/**/*.h
> /usr/include/bits/local_lim.h:#define PTHREAD_STACK_MIN 16384
> /usr/include/pthread.h:   minimal size of the block must be 
> PTHREAD_STACK_MIN.*/
> /usr/include/pthread.h:   to be started.  This size must never be less 
> than PTHREAD_STACK_MIN
> $ _
> 
> You can't have a stack smaller than 16KB as far as I understand. I seem 
> to recall the default stack size is much bigger.

On Windows I think the default size is 1MB.