The main difference between spinlock and mutex is that, in the spinlock mechanism, a thread trying to acquire the lock has to wait in the loop and repeatedly check for its availability, but in the case of mutex, multiple processes can take turns sharing the same resource.
When multiple processes access and manipulate the same data simultaneously, the outcome depends on the order of executing the processes. It is called a race condition. Executing multiple processes or threads can cause a race condition. Thus, it can lead to data inconsistency. Spinlock and mutex are two techniques to synchronize processes or threads.
Key Areas Covered
Locking Mechanism, Mutex, Spinlock, Threads
What is Spinlock
Spinlock is a locking mechanism. It allows a thread to wait until the lock is available. That is; a thread waits in a loop or spin until the lock is available.
After acquiring the lock, the thread holds the spinlock until releasing it. In some implementations, a spinlock may be automatically released if the thread holding the lock is blocked or goes to sleep state.
Moreover, a spinlock avoids overhead from OS process rescheduling or context switching. Furthermore, the spinlock is an efficient method to block the threads for a small period of time. Therefore, most operating system kernels use spinlocks. However, if a particular thread holds a spinlock for a long time, it can avoid other threads from executing. In this kind of situation, other threads continuously try to acquire the lock while the thread holding the lock does not initiate to release it. Especially, this can commonly occur in a single processor system.
Above all, it is a challenging task to implement spinlock as the programmer has to consider the simultaneous access to the lock, which can cause a race condition. However, it is possible to implement it using assembly language instructions such as an atomic test and set. With high-level languages, non-atomic locking algorithms such as Peterson algorithm can be used. Nevertheless, the drawback of using it with a high-level language is that it can require more memory than a spinlock.
What is Mutex
Mutex or mutual exclusion object is another locking mechanism. A process acquires the mutex before accessing the shared resource. Later, the process releases the lock. Likewise, only one process accesses the shared resource at a time. Therefore, this locking mechanism makes only one process to execute in the critical section at a time.
When the process needs to use the shared resource or to access a shared variable, it occupies the lock using acquire() operation. After completing the execution on the critical section, it releases the lock using the release() operation. When a particular process has the lock, the other processes cannot use the shared variable or execute in the critical section. They have to wait in the queue until the mutex is unlocked.
Difference Between Spinlock and Mutex
Spinlock is a lock which causes a thread trying to acquire it to simply wait in the loop and repeatedly check for its availability. In contrast, a mutex is a program object that is created so that multiple processes can take turns sharing the same resource. Thus, this is the main difference between spinlock and mutex.
Also, another difference between spinlock and mutex is that the spinlock blocks a thread for a short period of time while the mutex can block a thread for a long period of time.
In spinlock, the task cannot sleep while waiting for the lock, whereas in mutex, the task can sleep while waiting for the lock. Hence, this is also a difference between Spinlock and Mutex
In brief, Spinlock and mutex are two techniques to synchronize the processes or threads. The main difference between spinlock and mutex is that, in the spinlock mechanism, a thread trying to acquire the lock has to wait in the loop and repeatedly check for its availability, but in the case of mutex, multiple processes can take turns sharing the same resource. In short, both are locking mechanisms but working differently.