Lockset mechanism in linux kernel

Lockset Mechanism in Linux kernel

1. Locks: Prevent multiple threads to access shared resources simultaneously by allowing only one thread to acquire “lock” at a time. When a lock is enabled for a thread, other threads are blocked from accessing the resources/memory.

2. Spinlocks: type of lock that busy-wait until lock becomes available. Suitable when wait time is short. Should be used with precaution because takes resources while waiting and can also call deadlocks.

   1. busywait: busywait means that the thread will repeatedly check if lock has been removed.  

3. Mutexes: This allows threads to block and be put to sleep while waiting for lock to become available. This doesn’t take resources because it is not busywaiting.

4. Semaphores: Semaphores maintain count to to represent the number of resources. Process update this count whenever a resource is in use.

   example:

    semaphore s = 1;
      
    # when thread is using the resource
   
    s-- ; # decrement s, to signal that it’s in use
    wait(s)
    // do_operation
       
    # after operation is done
    s++; # increment again when lock has been removed
   

5. Atomic Operations: Some operations don’t need locking mechanism and should always be running in background, atomic operations are these types of operations. They are free from any locks.*

6. Read-Copy Update(RCU): RCU is a synchronization mechanism used in linux kernel to manage multiple read of memory synchronously. Particularly usefule where reads significantly outnumber writes.