"MAP_ANONYMOUS|MAP_SHARED mapped memory can only be accessed by the process which does that mmap() call or its child processes. There is no way for another process to map the same memory because that memory can not be referred to from elsewhere since it is anonymous."
misunderstanding what I meant by "file-backed memory"
No, it started by talking about using atomics for lock free interprocess communication, something MAP_ANONYMOUS can't do.
You hallucinated writing to storage as being part of this, didn't explain yourself and are getting upset about it. Atomic instructions that manipulate memory is orthogonal to what the OS does is the background. No one would think an operation on the order of nanoseconds has anything to do with writing permanent storage.
clarify the context (e.g. what OS you're talking about)
This thread is about mmap - it says it in the title.
it has nothing at all to do with any files or filepaths.
Two processes need some way to map the same memory and they do it through file paths.
> This thread is about mmap - it says it in the title.
I was asking what YOU are talking about. And also, this thread is actually about the approach of memory-mapped file I/O, not about POSIX mmap() specifically.
That's why I was (clearly) making statements that are not tied to any particular OS or platform, from the beginning.
https://stackoverflow.com/questions/4991533/sharing-memory-b...
misunderstanding what I meant by "file-backed memory"
No, it started by talking about using atomics for lock free interprocess communication, something MAP_ANONYMOUS can't do.
You hallucinated writing to storage as being part of this, didn't explain yourself and are getting upset about it. Atomic instructions that manipulate memory is orthogonal to what the OS does is the background. No one would think an operation on the order of nanoseconds has anything to do with writing permanent storage.
clarify the context (e.g. what OS you're talking about)
This thread is about mmap - it says it in the title.
it has nothing at all to do with any files or filepaths.
Two processes need some way to map the same memory and they do it through file paths.