CODEWITHSUNDEEP
linuxarchitecturelinux-kerneloperating-systemkernel
Satu0King
Satu0King

Reputation: 157

How does operating system preempt a process and regain control?

When a process is running on a CPU, the operating system is not running in the background as a single core CPU can execute only 1 instruction at a time. Then how does the operating system preempt a process, is it done by the hardware? I couldn't find an answer anywhere

Upvotes: 1

Views: 529

Answers (1)

o_in25
o_in25

Reputation: 136

To understand how the OS regains control of a process, the concept of interrupts must be understood. An interrupt is a signal sent to the CPU that signifies that the current processes must be stopped (i.e. interrupted) so that another process can begin. In some sense, this is accomplished at the hardware level as there are dedicated registers in the CPU that interrupting bits are placed in.

When an interrupt occurs, the contents of the CPU's registers are stored, the current stack pointer is saved, and the program counter is then pointed to the next instruction set forth by the scheduler that decides which process to begin next - usually the interrupting one. Barring deadlock, in which no progress on any processes can be made - the scheduler will make its way back to the original process, and that process's executing context will be reloaded into the machine (since we saved it prior). This concept of saving the state of the machine, executing a new process, and returning to the original process is known as a context switch. More on that here

Upvotes: 1

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