Inter-process Communication and Process Scheduling Flashcards
Process states transitions?
Processes can be in states such as new, ready, running, waiting or terminated, transitions include:
- new -> ready (process admitted)
- ready -> running (scheduler dispatch)
- running -> waiting (i/o request)
- running -> ready (time splice expire)
- waiting -> ready (i/o completion)
- running -> terminated (process completion)
Process vs threads
- Process is an independent program with its own memory space
- Thread is a smaller unit of execution within a process that shares memory and resources with other threads in the same process
Biggest advantage of implementing threads in user space
Fast context switching as it avoids kernel mode
Biggest disadvantage of implementing threads in user space
Threads in user space are not visible to the OS, leading to challenges in handling blocking system calls and scheduling
Threads concept utilised in practical applications?
- Web servers to handle multiple client requests simultaneously
- GUI applications for responsiveness
- Computational tasks to parrelise work
What is meant by Critical section problem?
A problem of ensuring that only one process accesses a critical section of code at a time to prevent race conditions
Why does the thread_yield call cause a thread to voluntarily give up the CPU?
It allows a thread to signal the schedular that it can suspend its execution to allow other threads to run, improving system responsiveness and fairness
Race condition definition?
A race condition occurs when two or more processes access shared resources concurrently, and the result depends on the timing of their execution
Deadlock, why can it occur and how to prevent?
- Deadlock occurs when processes are waiting on each other indefintely
- Prevention strategies include resource ordering, deadlock detection and avoiding circular wait conditions
Fork() and child process, how many processes or child processes are created?
Each fork() call creates one child process, for n fork() calls, up to 2^n processes can be created, including the parent process
Scheduling algorithm First Come First Served (FCFS)?
- Executes processes in the order they arrive, simplest non-preemptive algorithm
- May lead to long waiting/turn-around time
Scheduling algorithm Shortest Job First (SJF)?
- Executes processes with the shortest execution time first, non-preemptive algorithm
- High throughput
- Minimises average turnaround time but can starve longer processes
What is the calculation for turnaround time?
Turnaround time = Completion time - Arrival time
What is the calculation for waiting time?
Waiting time = Turnaround time - Burst time
What is deadlock?
Processes are unable to proceed as each is waiting for the other
What is livelock?
Processes continually change state in response to each other, without making progress
What is starvation?
One process is overlooked indefinitely by the schedular
