cooperative multitasking

parallel, operating system A form of multitasking where it

is the responsibility of the currently running task to give up

the processor to allow other tasks to run. This contrasts

with pre-emptive multitasking where the task scheduler

periodically suspends the running task and restarts another.

Cooperative multitasking requires the programmer to place

calls at suitable points in his code to allow his task to be

descheduled which is not always easy if there is no obvious

top-level main loop or some routines run for a long time.

If a task does not allow itself to be descheduled all other

tasks on the system will appear to "freeze" and will not

respond to user action.

The advantage of cooperative multitasking is that the

programmer knows where the program will be descheduled and can

make sure that this will not cause unwanted interaction with

other processes. Under pre-emptive multitasking, the

scheduler must ensure that sufficient state for each process

is saved and restored that they will not interfere. Thus

cooperative multitasking can have lower overheads than

pre-emptive multitasking because of the greater control it

offers over when a task may be descheduled.

Cooperative multitasking is used in RISC OS, MicrosoftWindows and Macintosh System 7.

(1995-03-20)