On 03-Apr-2006, John Meacham
On Mon, Apr 03, 2006 at 02:00:33PM -0400, Wolfgang Thaller wrote:
About how fast thread-local state really is: __thread attribute on Linux: ~ 2 memory load instructions. __declspec(thread) in MSVC++ on Windows: about the same. pthread_getspecific on Mac OS X/x86 and Mac OS X/G5: ~10 instructions pthread_getspecific on Linux and TlsGetValue on Windows: ~10-20 instructions pthread_getspecific on Mac OS X/G4: a system call :-(.
how prevelant is support for __thread BTW? is it required by any standards or an ELFism?
It's a recent innovation that standards have not yet had time to catch up with. But __thread is the way of the future, IMHO. GNU C/C++ supports __thread for at least the following architectures: IA-32, x86-64, IA-64, SPARC (32- and 64-bit), Alpha, S390 (31- and 64-bit), SuperHitachi (SH), HP/PA 64-bit. It's also supported by Borland C++ builder, Sun Studio C/C++, and Visual C++. (VC++ does use a slightly different syntax, but you can use macros to work around that.) -- Fergus J. Henderson | "I have always known that the pursuit Galois Connections, Inc. | of excellence is a lethal habit" Phone: +1 503 626 6616 | -- the last words of T. S. Garp.