CH5 - Process Synchronization

Processes can execute ___________

Concurrency

The Producer Code

while (true) {
	while (counter == BUFFER_SIZE) ;
	/* Do nothing */
	buffer[in] = next_produced;
	in = (in+1) % BUFFER_SIZE;
	counter ++;
}

The Consumer Code

while (true) {
	while (counter == 0) ;
	/* do nothing */
	next_consumed = buffer[out];
	out = (out+1) % BUFFER_SIZE;
	counter --;
}

Race Condition

several processes access and manipulate the same data concurrently and the outcome of the execution depends on the particular order in which the access takes place

Critical Section

section of code where shared data is accessed

In critical section process may change ________________, _____________, _____________.

• common variables

• updating table

• writing file

Entry Section

Code that request permission to enter its critical section

Exit Section

code that is run after exiting critical section

Mutual Exclusion

process Pi is executing in its critical section, then no other processes can be executing in their critical sections

Progress

Processes waiting to enter the critical section cannot be postponed indefinitely

Bounded Waiting

bound on how many times other processes can enter the critical sections after the request and before that request is granted

Preemptive Kernel

allows preemption of process when running in kernel mode

Non-preemptive Kernel

runs until exits kernel mode, blocks, or voluntarily yields CPU

Peterson’s Solution only we there are _________ processes

two

Peterson’s Solution Code

do {
	flag[i] = true;
	turn = j;
	while (flag[j] && trun == j) ;
	/* Critical section*/
	flag[i] = false;
	/* Reminder section */
} while (true);

Mutex Lock

software tool to solve critical section problem

Semaphore

software construct that can be used to enforce mutual exclusion

Deadlock

two or more processes are waiting indefinitely for an event that can be caused by only one of the waiting processes

Starvation

A process may never be removed from the semaphore queue in which it is suspended

Priority Inversion

Scheduling problem when lower-priority process holds a lock needed by higher-priority process

Priority Inversion solved via ____________

Priority-inheritance protocol