Apple does a hybrid with Mach and wants a real one.
I know that XNU is based on a chimera between OSF Mach and FreeBSD, but I'm pretty sure most practical u-kernel gains are lost in this process. They do have the basic resources like tasks, threads, VM and IPC with its system of port rights checking, but it's mostly leveraged as a convenient abstraction at best. I don't think OS X even supports per-application default memory managers, does it?
However, what you said about "wants a real one" really piqued my interest. Is it true Apple is researching pure microkernel designs for their products? That sounds great, do share some links.
Yeah, that and some basic functions are all they use it for. A write up way back indicated they though Mach was a mistake. So, the alternatives were a better microkernel or full monolithic. One unofficial project tried to port it to L4. Not sure what Apple's stance is under Tim Cook, though.
I know that XNU is based on a chimera between OSF Mach and FreeBSD, but I'm pretty sure most practical u-kernel gains are lost in this process. They do have the basic resources like tasks, threads, VM and IPC with its system of port rights checking, but it's mostly leveraged as a convenient abstraction at best. I don't think OS X even supports per-application default memory managers, does it?
However, what you said about "wants a real one" really piqued my interest. Is it true Apple is researching pure microkernel designs for their products? That sounds great, do share some links.