Contents
- 1 Is there busy waiting in semaphore?
- 2 When you signal a semaphore Do you know if another process is waiting?
- 3 Is a queue of threads waiting for something inside a critical section?
- 4 What is the purpose for a semaphore queue?
- 5 What is the initial value of a semaphore?
- 6 Why are semaphores a problem in process synchronization?
Is there busy waiting in semaphore?
The main disadvantage of the semaphore is that it requires busy waiting. Busy waiting wastes CPU cycles that some other process might be able to use productively. This type of semaphore is also called a spinlock because the process spins while waiting for the lock.
When you signal a semaphore Do you know if another process is waiting?
Difference between Semaphore vs. Mutex
| Parameters | Semaphore |
|---|---|
| Resource management | If no resource is free, then the process requires a resource that should execute wait operation. It should wait until the count of the semaphore is greater than 0. |
| Thread | You can have multiple program threads. |
Do semaphores have waiting queues?
Semaphores can be implemented inside the operating system by interfacing with the process state and scheduling queues: a thread that is blocked on a semaphore is moved from running to waiting (a semaphore-specific waiting queue).
Is a queue of threads waiting for something inside a critical section?
Condition variable: is a queue of threads waiting for something inside a critical section. Condition variables support three operations: Rule: thread must hold the lock when doing condition variable operations.
What is the purpose for a semaphore queue?
When used to control access to a pool of resources, a semaphore tracks only how many resources are free; it does not keep track of which of the resources are free. Some other mechanism (possibly involving more semaphores) may be required to select a particular free resource.
How to understand Wait and signal in Semaphore?
A simple way to understand wait (P) and signal (V) operations is: wait: Decrements the value of semaphore variable by 1. If the new value of the semaphore variable is negative, the process executing wait is blocked (i.e., added to the semaphore’s queue). Otherwise, the process continues execution,…
What is the initial value of a semaphore?
The initial value of the Semaphore variable is ‘1’. 1 means that the resource is free and the process can enter the critical section. If the value of S is ‘0’ this means that some other process is in its critical section and thus, the current process should wait.
Why are semaphores a problem in process synchronization?
The main problem with semaphores is that they require busy waiting, If a process is in the critical section, then other processes trying to enter critical section will be waiting until the critical section is not occupied by any process.
How to remove a semaphore from a process?
This flag may be set in the sem_flg member passed in the sembuf argument semop, and it will, as the name suggests, undo semaphore adjustments upon process termination. IIUC, when you kill a client, that client leaves a semaphore inappropriately locked. SEM_UNDO was made for just this circumstance.