In article <004e01c53ac9$35901640$6601a8c0@pdimov>, "Peter Dimov" <pdimov@mmltd.net> wrote:
or something like that. Post-release. The current code is good (and risky) enough. :-)
My understanding from having spoken to several Apple engineers whom I consider knowledgeable on this topic is that it's a very bad idea to write assembly code to perform atomic operations on the PPC. There is a variety of CPU-specific idiosyncracies that make it very difficult to write such code correctly. As you might imagine, writing such code not quite correctly leads bugs that are very hard to track down. This recommendation is explicit in Apple's documentation at <http://developer.apple.com/technotes/tn/tn2006.html>: "Do not use the PowerPC instructions Load Reserved (lwarx) and Store Conditional (stwcx) to implement atomicity in your preemptively threaded application. As described in DTS Technote 1137 Disabling Interrupts on the Traditional Mac OS, these instructions are non-portable and are tricky to use correctly across the full spectrum of PowerPC implementations." For this reason, Apple supplies a number of atomic primitives in Mac OS 9 and Mac OS X which perform a variety of modify-or-fail primitives; Apple takes it upon themselves to make sure that their implementation is correct for the CPU architectures that the OS supports, and I can guarantee you that Apple has more time to develop and test these across a wide range of PPC hardware than we ever will (or should try to). I cannot understate how important it is that use the Apple APIs. They are documented at <http://developer.apple.com/documentation/Hardware/DeviceManagers/pci_srvcs/p... ards_drivers/PCI_BOOK.1a3.html>. Do not be concerned about the fact that this documentation is for PCI drivers; the same APIs are available in userland with #include <CoreServices/CoreServices.h>. meeroh