Comment by kazinator
7 years ago
CreateProcess requires an application to initialize from scratch. When you fork, you cheaply inherit the initialized state of the whole application image. Only a few pages that are mutated have to be subject to copy-on-write. Even that copy-on-write is cheaper than calculating the contents of those pages from scratch.
There has been a lot of discussion in recent years about how cheap that "cheaply" really is.
* https://news.ycombinator.com/item?id=19622503
Yeah, it's not really cheap at all. However! vfork() is cheap, very very cheap, though, of course, you then have to follow it up with an exec(), and the cost of that on Windows depends on the setup cost of the executable being exec'ed.
Part of the problem is the DLLs, as many have mentioned, and also the fact that each statically links in its own CRT (C run-time). The shared C run-time MSFT is working on should help here. As should more lazy loading and setup.
> Part of the problem is the DLLs, as many have mentioned, and also the fact that each statically links in its own CRT (C run-time)
No, that isn't the case on DLLs shipped with Windows.
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fork is pretty much always going to be cheaper than starting a new process in scratch over the same executable image (and library images) and then re-playing everything inside that process so that it gets into exactly the same state as the creator to be a de facto clone of it.