Re: [TUHS] "Fork considered harmful"

Having read this, and seen the subsequent discussion, I think both sides have good points. What I perceive to be happening is something I've described previously, but never named, which is that as a system scales up, it can be necessary to take one subsystem which did two things, and split it up so there's a custom subsystem for each. I've seen this a lot in networking; I've been trying to remember some of the examples I've seen, and here's the best one I can come up with at the moment: having the routing track 'unique-ID network interface names' (i.e. interface 'addresses') - think 48-bit IEEE interface IDs' - directly. In a small network, this works fine for routing traffic, and as a side-benefit, gives you mobility. Doesn't scale, though - you have to build an 'interface ID to location name mapping system', and use 'location names' (i.e. 'addresses') in the routing. So classic Unix 'fork' does two things: i) creates a new process, and ii) replicates the environment/etc of an existing process. (In early Unix, the latter was pretty simple, but as the paper points out, it has now become a) complex and b) expensive.) I think the answer has to include decomposing the functionality of old fork() into several separate sub-primitives (albeit not all necessarily directly accessible to the user): a new-process primitive, which can be bundled with a number of different alternatives (e.g. i) exec(), ii) environment replication, iii) address-space replication, etc) - perhaps more than one at once. So that shell would want a form of fork() which bundled in i) and ii), but large applications might want something else. And there might be several variants of ii), e.g. one might replicate only environment variables, another might add I/O channels, etc. In a larger system, there's just no 'one size fits all' answer, I think. Noel