On Thu, Mar 14, 2013 at 12:59:57PM -0700, Stefan Ring wrote:
> > Yup, in fact, if I hadn't come up with the __read[gf]sword() trick,
> > my only other option would have been TLS (or the GetCurrentThreadId
> > /pthread_self() approach in the presentation). TLS is fantastic,
> > and it's definitely an intrinsic part of the solution (the "Y" part
> > of "if we're a parallel thread, do Y"), but it definitely more
> > costly than a simple FS/GS register read.
>
> I think you should be able to just take the address of a static
> __thread variable to achieve the same thing in a more portable way.
Sure, but, uh, that's kinda' trivial in comparison to all the wildly
unportable Windows-only functionality I'm using to achieve all of
this at the moment :-)
For the record, here are all the Windows calls I'm using that have
no *direct* POSIX equivalent:
Interlocked singly-linked lists:
- InitializeSListHead()
- InterlockedFlushSList()
- QueryDepthSList()
- InterlockedPushEntrySList()
- InterlockedPushListSList()
- InterlockedPopEntrySlist()
Synchronisation and concurrency primitives:
- Critical sections
- InitializeCriticalSectionAndSpinCount()
- EnterCriticalSection()
- LeaveCriticalSection()
- TryEnterCriticalSection()
- Slim read/writer locks (some pthread implements have
rwlocks)*:
- InitializeSRWLock()
- AcquireSRWLockShared()
- AcquireSRWLockExclusive()
- ReleaseSRWLockShared()
- ReleaseSRWLockExclusive()
- TryAcquireSRWLockExclusive()
- TryAcquireSRWLockShared()
- One-time initialization:
- InitOnceBeginInitialize()
- InitOnceComplete()
- Generic event, signalling and wait facilities:
- CreateEvent()
- SetEvent()
- WaitForSingleObject()
- WaitForMultipleObjects()
- SignalObjectAndWait()
Native thread pool facilities:
- TrySubmitThreadpoolCallback()
- StartThreadpoolIo()
- CloseThreadpoolIo()
- CancelThreadpoolIo()
- DisassociateCurrentThreadFromCallback()
- CallbackMayRunLong()
- CreateThreadpoolWait()
- SetThreadpoolWait()
Memory management:
- HeapCreate()
- HeapAlloc()
- HeapDestroy()
Structured Exception Handling (#ifdef Py_DEBUG):
- __try/__except
Sockets:
- ConnectEx()
- AcceptEx()
- WSAEventSelect(FD_ACCEPT)
- DisconnectEx(TF_REUSE_SOCKET)
- Overlapped WSASend()
- Overlapped WSARecv()
Don't get me wrong, I grew up with UNIX and love it as much as the
next guy, but you can't deny the usefulness of Windows' facilities
for writing high-performance, multi-threaded IO code. It's decades
ahead of POSIX. (Which is also why it bugs me when I see select()
being used on Windows, or IOCP being used as if it were a poll-type
"generic IO multiplexor" -- that's like having a Ferrari and speed
limiting it to 5mph!)
So, before any of this has a chance of working on Linux/BSD, a lot
more scaffolding will need to be written to provide the things we
get for free on Windows (threadpools being the biggest freebie).
Trent.
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