What is mutual exclusion in operating system?

In computer science, mutual exclusion is a property of concurrency control, which is instituted for the purpose of preventing race conditions. … This problem (called a race condition) can be avoided by using the requirement of mutual exclusion to ensure that simultaneous updates to the same part of the list cannot occur.

It is the requirement that a process can not enter its critical section while another concurrent process is currently present or executing in its critical section i.e only one process is allowed to execute the critical section at any given instance of time. Mutual exclusion in single computer system Vs.

Mutual Exclusion: Exclusive access of each process to the shared memory. Progress: If no process is in its critical section, and if one or more threads want to execute their critical section then any one of these threads must be allowed to get into its critical section.

Perhaps the most obvious way of achieving mutual exclusion is to allow a process to disable interrupts before it enters its critical section and then enable interrupts after it leaves its critical section. … This guarantees that the process can use the shared variable without another process accessing it.

Critical Section and Mutual Exclusion: That part of the program where the shared memory is accessed is called critical section. … Mutual Exclusion: It is some way of making sure that if one process is using a shared variable or file, the other process will be excluded from doing the somethings.

In an operating system, a deadlock occurs when a process or thread enters a waiting state because a requested system resource is held by another waiting process, which in turn is waiting for another resource held by another waiting process.

1. Mutual exclusion. Make some resources unsharable, such as printers, tape drives.
2. Hold and wait. Process must request all needed resources at one time. …
3. No Preemption. Make it possible for the O/S to make a process give up a resource. …
4. Circular wait.

Counting Semaphore has no mutual exclusion whereas Binary Semaphore has Mutual exclusion. Semaphore means a signaling mechanism whereas Mutex is a locking mechanism. Semaphore allows more than one thread to access the critical section. One of the biggest limitations of a semaphore is priority inversion.

Mutual Exclusion: Only one process can be in the critical section at a time — otherwise what critical section?. … Bounded Waiting: No process can wait forever for a resource — otherwise an easy solution: no one gets in.

Because they avoid overhead from operating system process rescheduling or context switching, spinlocks are efficient if threads are likely to be blocked for only short periods. For this reason, operating-system kernels often use spinlocks.

In computer science, the ostrich algorithm is a strategy of ignoring potential problems on the basis that they may be exceedingly rare. It is named after the ostrich effect which is defined as “to stick one’s head in the sand and pretend there is no problem”.

Deadlock frequency can sometimes be reduced by ensuring that all applications access their common data in the same order – meaning, for example, that they access (and therefore lock) rows in Table A, followed by Table B, followed by Table C, and so on.

7 Seven Cases of Deadlocks  Non-sharable /non-preemptable resources –Allocated to jobs requiring same type of resources  Resource types locked by competing jobs –File requests –Databases –Dedicated device allocation –Multiple device allocation –Spooling –Disk sharing –Network Homework: Read about these cases in the …

1. Breaking mutual exclusion. In some cases, deadlock can be mitigated by making resources more shareable. …
2. Breaking no-preemption. In some situations we can make resources preemptable. …
3. Breaking hold-and-wait. …
4. Breaking circular wait: lock ordering.

[Mutual exclusion:] Concurrently running threads may attempt to update the same memory location simultaneously. Without a mechanism to guarantee mutual exclusion, shared variables may become corrupted, causing an indeterministic result.

As mentioned, a counting semaphore can allow multiple processes or threads to access the critical section, hence mutual exclusion is not guaranteed. Since multiple instances of process can access the shared resource at any time, counting semaphore guarantees bounded wait.

Semaphores for mutual exclusion are a sub-category of all semaphores. They are used to block access to a resource, usually. … Start all the processes and signal the semaphore once. One of the waiting processes will get to go; then it will signal the semaphore, and another process waiting will go; etc.

In TestAndSet, Mutual exclusion and progress are preserved but bounded waiting cannot be preserved.

Mutual exclusion is a mechanism to ensure that only one process (or person) is doing certain things at one time, thus avoid data inconsistency. All others should be prevented from modifying shared data until the current process finishes. Strict Alternation (see Fig.

Deadlock means no progress and progress not related to Bounded Wait . Deadlock not related to BW . If there is a deadlock , bounded waiting can possible. But progress can not possible.

SpinLock are typically used when working with interrupts to perform busy waiting inside a loop till the resource is made available. SpinLock don’t cause the thread to be preempted, rather, it continues to spin till lock on the resource is released.

Spin Wait. A spin wait that you have to wait until condition for thread is true. Spin Loop. Spin loop is also similar to both of above busy spin and wait spin. It means that threads have to wait for other thread for completing his work.

The basic form of locking in the Linux kernel is the spinlock. Spinlocks take their name from the fact that they continuously loop, or spin, waiting to acquire a lock. … This section of code sets the spin_lock to “unlocked,” or 0, on line 66 and initializes the other variables in the structure.

5. Low and high load performance. The load is determined by the arrival rate of critical section execution requests. Performance of a mutual exclusion algorithm depends upon the load and we often study the performance of mutual exclusion algorithms under two special loading conditions, viz., “low load” and “high load”.

Which mutual exclusion algorithm is useful when the membership of the group is unknown? Lamport’s.

Que.What are the three popular semantic modes ?b.Unix, Transaction & Session semanticsc.Coherent, Transaction & Session semanticsd.Session, Coherent semanticsAnswer:Unix, Transaction & Session semantics

The banker’s algorithm is a resource allocation and deadlock avoidance algorithm that tests for safety by simulating the allocation for predetermined maximum possible amounts of all resources, then makes an “s-state” check to test for possible activities, before deciding whether allocation should be allowed to continue …

Convoy Effect is phenomenon associated with the First Come First Serve (FCFS) algorithm, in which the whole Operating System slows down due to few slow processes. … While the CPU intensive process is being executed, the I/O bound processes complete their I/O operations and are moved back to ready queue.

Stick your head in the sand and pretend there is no problem at all, this method of solving any problem is called Ostrich Algorithm. The method of solving any problem varies according to the people.

• Resource Deadlock. Occurs when processes are trying to get exclusive access to devices, files, locks, servers, or other resources. …
• Communication Deadlock.

Necessary Conditions of Deadlock Mutual Exclusion: A resource can be held by only one process at a time. In other words, if a process P1 is using some resource R at a particular instant of time, then some other process P2 can’t hold or use the same resource R at that particular instant of time.

• Mutual Exclusion: …
• Hold and Wait: …
• No Preemption: …
• Circular Wait: