2 ms·

It's because you treat it as if it's all or nothing. You can effectively allow apps to cooperatively schedule themselves, but also make sure `while(true){}` doe

It's because you treat it as if it's all or nothing. You can effectively allow apps to cooperatively schedule themselves, but also make sure `while(true){}` doesn't infinitely loop the system. You can e.g. timeout each app, or if you feel very experimental, avant-garde etc, you could try detecting loops, and put a very generous timeout (since you'll miss some loops like `i=0;while(true){i+=1}` depending on the algo you use to detect loops). There are tons of other schemes, algorithms. Most of these ideas are implemented somewhere, but 99.9% of computer users using linux/OSX/Windows don't experience them. For the programmer, it's most convenient when the isolation between unrelated programs is maximal but isolation between related programs is minimal; but for the user it's the most convenient when programs are maximally isolated in terms of computation, but not for other things such as storage/permissions etc. Practically, this requires a complex scheduling mechanism that is more preemptive than cooperative, but also cooperative a little. E.g. in linux, it's not particularly hard for a rogue program to bring the system to halt with something like a fork bomb (especially if swap is turned on). Even if you have a preemptive scheduler, if your program has 99% of the threads running in the system, it's effectively cooperative because chances are you're scheduled most of the time anyway.

DSMan195276 3y ago
The problem is that it really _is_ an all or nothing, there are assumptions that cooperative programs will make that break if they can be preempted at any point. Even having a "little" preemption means programs have to be written to assume it can happen at any time (unless preemption means killing the program entirely).
- getpokedagain 3y ago
  I get what you are saying but does every operating system have the goal of allowing unpredictable multiple user applications running? A cooperative system can easily be correct for something well managed like an IOT device with only certain tasks or something somewhat general purpose but still more restricted like a video game console.
  - DSMan195276 3y ago
    > I get what you are saying but does every operating system have the goal of allowing unpredictable multiple user applications running? Certainly not, cooperative multitasking is used all the time in userspace programs to great effect, and OSs can do the same thing if the limitations are understood. For the OS that's the focus of this post though, I think it does have the aim of being general purpose and running whatever you want on it. At that point the limitations aren't really acceptable (which the author acknowledges), and that's why the whole question of "what happens when a program misbehaves?" has come up. If the answer is "preempt the process to run it later" then it's not actually a cooperative system and application developers need to keep that in mind.

DSMan195276 3y ago

The problem is that it really _is_ an all or nothing, there are assumptions that cooperative programs will make that break if they can be preempted at any point. Even having a "little" preemption means programs have to be written to assume it can happen at any time (unless preemption means killing the program entirely).

getpokedagain 3y ago
I get what you are saying but does every operating system have the goal of allowing unpredictable multiple user applications running? A cooperative system can easily be correct for something well managed like an IOT device with only certain tasks or something somewhat general purpose but still more restricted like a video game console.
- DSMan195276 3y ago
  > I get what you are saying but does every operating system have the goal of allowing unpredictable multiple user applications running? Certainly not, cooperative multitasking is used all the time in userspace programs to great effect, and OSs can do the same thing if the limitations are understood. For the OS that's the focus of this post though, I think it does have the aim of being general purpose and running whatever you want on it. At that point the limitations aren't really acceptable (which the author acknowledges), and that's why the whole question of "what happens when a program misbehaves?" has come up. If the answer is "preempt the process to run it later" then it's not actually a cooperative system and application developers need to keep that in mind.