Difference Between Semaphore and Monitor

The basic difference between semaphore and monitor is that the semaphore is an integer variable S which indicate the number of resources available in the system whereas, the monitor is the abstract data type which allows only one process to execute in critical section at a time.

1. What advantage do monitors have over Semaphore?
2. What is the difference between Semaphore and condition variable?
3. How are semaphores used to implement monitors?
4. What is a semaphore used for?
5. What are the four necessary conditions for deadlock?
6. What are the advantages and disadvantages of Semaphore?
7. What are condition variables in monitors?
8. Why is mutex used?
9. What is mutex variable?
10. Which characteristics of monitors mark them as high level synchronization tools?

What advantage do monitors have over Semaphore?

Advantages of Monitors:

Monitors can overcome the timing errors that occur while using semaphores. Shared variables are global to all processes in the monitor while shared variables are hidden in semaphores.

What is the difference between Semaphore and condition variable?

Condition Variable, as name suggests, is simply a synchronization primitive that allows threads to wait until particular condition occurs. It includes two operations i.e., wait and signal.
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Difference between Semaphore and Condition Variable :

How are semaphores used to implement monitors?

5.8.3 Implementing a Monitor Using Semaphores

For each monitor, a semaphore mutex (initialized to 1) is provided. A process must execute wait(mutex) before entering the monitor and must execute signal(mutex) after leaving the monitor. wait(mutex); ... body of F ... if (next count > 0) signal(next); else signal(mutex);

What is a semaphore used for?

In computer science, a semaphore is a variable or abstract data type used to control access to a common resource by multiple processes and avoid critical section problems in a concurrent system such as a multitasking operating system.

What are the four necessary conditions for deadlock?

4 Conditions for Deadlock

• mutual exclusion: at least one process must be held in a non-sharable mode.
• hold and wait: there must be a process holding one resource and waiting for another.
• No preemption: resources cannot be preempted.
• circular wait: there must exist a set of processes.

What are the advantages and disadvantages of Semaphore?

In semaphores there is no spinning, hence no waste of resources due to no busy waiting. That is because threads intending to access the critical section are queued.

What are condition variables in monitors?

A condition variable essentially is a container of threads that are waiting for a certain condition. Monitors provide a mechanism for threads to temporarily give up exclusive access in order to wait for some condition to be met, before regaining exclusive access and resuming their task.

Why is mutex used?

Mutex or Mutual Exclusion Object is used to give access to a resource to only one process at a time. The mutex object allows all the processes to use the same resource but at a time, only one process is allowed to use the resource. Mutex uses the lock-based technique to handle the critical section problem.

What is mutex variable?

A mutex is a thread synchronization object, it can be used by threads to control access to a shared resource. A mutex can be locked to indicate a resource is in use, and other threads can then block on the mutex to wait for the resource (or can just test and do something else if not available).

Which characteristics of monitors mark them as high level synchronization tools?

Which characteristics of monitors mark them as high-level synchronisation tools? 1) As the variables and procedures are encapsulated, local data variables are accessible only by the monitor's procedures and not by any external procedure, thus eliminating the erroneous updating of variables.