Removing The Global GC Lock: Largest Plausible Number of Threads?

[Daniel Gibson]

Am 12.05.2011 06:47, schrieb Daniel Gibson:
> Am 12.05.2011 06:33, schrieb Jonathan M Davis:
>> On 2011-05-11 21:14, dsimcha wrote:
>>> I'm thinking about ways to remove the global lock from the garbage
>>> collector for most small allocations.  I'm basically thinking of making
>>> the free lists thread local.  Every scheme I can come up with that
>>> doesn't require a radical overhaul of the current implementation
>>> requires every thread having a unique ID.  I want to do this as simply
>>> and efficiently as possible, preferably using dense integers.  Is it
>>> reasonable to assume that no program will ever need more than 2 ^^ 16
>>> thread (about 65,000) simultaneously so that I can store these indices
>>> as ushorts?  If a program creates a lot of short-lived threads, the
>>> indices will be recycled, so having a huge number of threads
>>> non-simultaneously is not a problem.
>>
>> I don't think that you can legally create that many threads on a typical OS. 
>> I'd have to check, but as I recall, the typical limit is much lower than that 
>> - still in the tens of thousands, I think, but not that high.
>>
>> - Jonathan M Davis
> 
> On Windows you get a DWORD (32bit int AFAIK) from GetCurrentThreadId(),
> so that seems to be a technical limit there.
> On Linux there's pthread_t which seems to be a 32bit uint on x86 and
> 64bit ulong on amd64.
> 
> However, see:
> http://stackoverflow.com/questions/344203/maximum-number-of-threads-per-process-in-linux
> It seems like it's limited by the available stack space (especially on
> 32bit systems)
> Similar on Windows:
> http://blogs.msdn.com/b/oldnewthing/archive/2005/07/29/444912.aspx
> 
> Cheers,
> - Daniel

Also:
http://www.sgi.com/products/servers/altix/uv/configs.html
You can actually buy systems with 2048 Cores (AMD64 architecture even)
and, thanks to Hyperthreading, 4096 threads (that may run at the same
time) that run Linux.
I think it isn't *that* unrealistic to have more than ushort.max Threads
on such a beast.