Hello! I am still attempt to better understand how concurrency
works. I read a lot of info but still misunderstood some
key-points.
Here is my thought about it and questions:
1. There is OS threads. Context-switching is very expensive
because during it we should to save ALL CPU registers to RAM.
Accessing to RAM is slowly up 200-300 times then accessing to
registers, so dumping/restoring registers take a lot of time.
Right?
1.1 During context-switching OS is go to kernel-mode (ring-0). I
have heard opinion that it's cost a lot, but can't understand is
it true and why it cost a lot?
2. Message passing is superstructure of threads. Right? When it
can be helpful? Any user-case please.
2.1 Can simple threads pass data/messages to each other without
message passing?
3. Fibers is threads that works in user-mode (rather in single
kernel-thread OS do not see them, it see only 1 own Thread).
3.1 Fibers are switch explicitly. If do not call yield
mother-thread will be hang on.
3.2 Where fibers store CPU register state in moment of switching
between fibers? In memory? But then what difference with
context-switching (that take a lot of time to save/restore
registers state)?
Please correct me where I am wrong and highlight where I am right.
