Are Fibers just broken in D?

[Steven Schveighoffer]

On 4/24/18 5:11 AM, bauss wrote:
> On Tuesday, 24 April 2018 at 07:58:01 UTC, Radu wrote:
>> On Tuesday, 24 April 2018 at 00:46:39 UTC, Byron Heads wrote:
>>>
>>> Fibers on Win32 have a memory leak for sure:
>>>
>>> import core.thread : Fiber;
>>>
>>> void main() {
>>>
>>>     foreach(ulong i; 0..99_999) {
>>>         auto foo = new Foo();
>>>         foo.call();
>>>         foo.call();
>>>     }
>>> }
>>>
>>>
>>> class Foo : Fiber {
>>>     this() {
>>>         super(&run);
>>>     }
>>>
>>>
>>>     void run() {
>>>         Fiber.yield();
>>>     }
>>> }
>>>
>>>
>>> Running this with -m64 on windows runs without a problem, but with 
>>> -m32 it failes aith a Memory Allocation failed error.
>>
>> This is not a fiber issue but a more memory management issue. Your run 
>> out of address space on win32, the GC will not always collect all 
>> those 99999 fibers that you allocate in that loop. As an exercise 
>> replace `auto` with `scope` like `scope foo = new Foo();` in that loop 
>> - you should see different results.

This shouldn't be a requirement, the 32-bit GC is generally not this bad.

>>
>> The issue boils down to the call to VirtualAlloc that the fiber 
>> constructor makes, which fails as Windows will not allocate any more 
>> virtual pages for the process. If you really want that many fibers you 
>> should reconsider 32 bit, and definitely use a different allocation 
>> strategy.
> 
> And in the end of the day it makes no sense to have that many fibers as 
> they would probably perform terrible.

Let's not forget though, that he's executing the fiber completely within 
the loop. It should be done and collected.

This is not the case of executing 100,000 concurrent fibers, but 
executing 100,000 *sequential* fibers. It should work just fine.

-Steve