Cooperative multitasking

Cooperative multitasking is a style of computer multitasking in which the operating system never initiates a context switch from a running process to another process. Instead, processes voluntarily yield control periodically or when idle or logically blocked, to enable multiple applications to be run concurrently. This contrasts with preemptive multitasking, where the operating system slices the CPU time and dedicates a slot to each of the programs.

Overview

In cooperative multitasking, a process holds the CPU until it either finishes its execution or decides to give up the CPU voluntarily. The system relies on each process to provide time to the other processes in a defined manner. This method was popular in early computing environments where the simplicity of the approach facilitated easier implementation of the operating system.

Advantages and Disadvantages

Advantages

• Simplicity: The implementation of cooperative multitasking is simpler compared to preemptive multitasking, as the operating system does not need to manage the timing and saving/restoring of process states.
• Performance: Without the overhead of context switching, applications may run slightly faster, especially if they are designed to cooperate well with others.

Disadvantages

• Reliability: A single misbehaving application can freeze the entire system, as it might never yield control back to the operating system.
• Responsiveness: The system may become unresponsive if a process does not yield control, making it unsuitable for time-critical applications.

Implementation

In environments where cooperative multitasking is employed, applications need to be specifically designed to ensure regular yielding to other processes. This is often achieved through the use of specific API calls that hand control back to the operating system, allowing it to decide which process to run next.

Historical Usage

Cooperative multitasking was widely used in early operating systems, such as early versions of Windows and Mac OS before the adoption of preemptive multitasking. These systems relied on well-behaved applications to ensure smooth operation.

Comparison with Preemptive Multitasking

While cooperative multitasking relies on the cooperation of each process, preemptive multitasking allows the operating system to control the scheduling of processes. This makes preemptive multitasking more suitable for modern computing environments where reliability and responsiveness are critical.

See Also

• Computer multitasking
• Operating system
• Process (computing)
• Scheduling (computing)