How you handle multi task?

Answer 1

Multi-tasking is a function of the operating system and gives the impression that two or more programs are running simultaneously. Systems that have two or more independent processors or cores are obviously capable of running two or more programs simultaneously, however only one program can physically run on any one core at any one point in time, and the number of running programs (or threads, since programs can be multi-threaded) typically exceeds the number of physical cores available. Thus programs must be scheduled so they each get a fair share of CPU time.

At the heart of the scheduler is the dispatcher followed by the short-term, mid-term and long term schedulers. The dispatcher is responsible for the low-level context switching. Switching tasks incurs a dispatch latency which means the CPU is momentarily idle. Thus the dispatcher must not only operate extremely quickly but must avoid any unnecessary context switching. The short-term scheduler is responsible for selecting tasks for dispatch. Typically, the short-term scheduler runs after every time slice and can force tasks off the CPU (pre-emptive scheduling). The mid-term scheduler is responsible for swapping tasks between memory and page files while the long-term scheduler decides which tasks should be admitted to the ready queue.

Between them, the schedulers prioritise tasks to ensure every task gets a fair share of the CPU, with higher priority tasks taking more time-slices than low-priority tasks. This is achieved through a variety of algorithms often used in some combination, such as first in first out, round robin, shortest job first, fixed-priority pre-emptive scheduling and multi-level scheduling, amongst others.