Jim Donelson wrote: > All that is really required is an atomic exchange. > Suppose 1 means taken, 0 means free. I do an exchange with a 1. If I got > back a zero, it's mine.
True with a Mutex, not true with a Futex. Here you need a second bit in user-space that tells the releaser that it is to wake up a sleeping waiter. Otherwise, any release would need a system call. Seemingly the best instruction to handle these bits is "atomic compare and exchange" (e.g. provided by the X86 CPU). OTOH with a load-store-architecture CPU it's not that simple to add a memory read-modify write instruction to the ISA, while it's no big problem to have such an instruction do with the data whatever is appropriate. -Michael _______________________________________________ uClinux-dev mailing list uClinux-dev@uclinux.org http://mailman.uclinux.org/mailman/listinfo/uclinux-dev This message was resent by uclinux-dev@uclinux.org To unsubscribe see: http://mailman.uclinux.org/mailman/options/uclinux-dev
