Does cooperative scheduling suspend processes when they perform an I/O operation?

Problem Detail: 

Many operating systems references say that with cooperative (as opposed to preemptive) multitasking, a process keeps the CPU until it explicitly voluntarily suspends itself. If a running process performs an I/O request that cannot be immediately satisfied (e.g., requests a key stroke that is not yet available), does the scheduler suspend it, or does it really keep the CPU until the request can be serviced?

[Edited to replace "blocks on i/o" with "performs an I/O request that cannot be immediately satisfied."]

Asked By : espertus

Answered By : Carl Mummert

In a truly "cooperative" setting, and if there was no hardware protection, a process could certainly block on I/O and not relinquish control until the I/O was done (or never relinquish control at all). For example, Windows 3.1 was this way: if a single user process wanted to take over the entire computer, and prevent anything else from running, it could.

But on a system with multitasking you expect the system API I/O commands to relinquish control of the processor when they are called. So when a running process blocks on I/O, assuming that the process uses the normal system APIs, other processes will be allowed to run until the I/O is complete, and eventually the original process will resume once the I/O is done. In other words, calling a blocking I/O function is one way that a process on a cooperative system can voluntarily suspend itself.

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Question Source : http://cs.stackexchange.com/questions/5