Why would you use a spin lock instead of a mutex?

If a thread cannot lock the mutex, it won’t be put to sleep immediately, since the mutex might get unlocked pretty soon, so instead the mutex will first behave exactly like a spinlock.

When should you use spinlocks?

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.

Are spinlocks good for latency?

In general application code, you’ll want to avoid spinlocks. In low-level stuff where you’ll only hold the lock for a couple of instructions, and latency is important, a spinlock mat be a better solution than a lock. But those cases are rare, especially in the kind of applications where C# is typically used.

What is difference between lock and mutex?

A lock allows only one thread to enter the part that’s locked and the lock is not shared with any other processes. A mutex is the same as a lock but it can be system wide (shared by multiple processes).

How do you stop spinning locks?

There are two ways to avoid this:

1. Do not acquire the lock. In many situations it is possible to design data structures that do not require locking, e.g. by using per-thread or per-CPU data and disabling interrupts.
2. Switch to a different thread while waiting.

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.

Can we use spinlock in interrupt handler?

The answer is yes and no. you can use the up and unlock, but you can’t use down and lock, as these are blocking calls which put the process to sleep and we are not supposed to sleep in interrupt handlers.

What is the disadvantage of spin lock?

The primary disadvantage of a spinlock is that, while waiting to acquire a lock, it wastes time that might be productively spent elsewhere. Do not acquire the lock. In many situations it is possible to design data structures that do not require locking, e.g. by using per-thread or per-CPU data and disabling interrupts.

Do mutexes spin?

There are also “adaptive mutexes” which will try to spin for a while and if they’re not successful, they’ll go to sleep to let other threads run. This is never a problem with two threads, but the more threads you have, the more likely you are to get those cases where one thread is left out for a very long time.

What does a mutex lock?

Strictly speaking, a mutex is a locking mechanism used to synchronize access to a resource. Only one task (can be a thread or process based on OS abstraction) can acquire the mutex. It means there is ownership associated with a mutex, and only the owner can release the lock (mutex).

Is semaphore A locking mechanism?

It is a locking mechanism. Semaphore is an integer variable. Mutex is just an object. The wait and signal operations can modify a semaphore.

Which is better a spinlock or a mutex?

If you search for this you’ll find lots of benchmarks that all come to the conclusion that spinlocks are better. (like this, this or this) What these benchmarks have in common is that they measure code in which there is nothing else to do except fight over the lock. In that environment the only thing that makes sense is to use a spinlock.

What’s the difference between spin lock and busy waiting?

Busy waiting= Continuosly testing of a variable until some value appears. Spin-lock (aka Spinlock) = A lock which uses busy waiting. (The acquiring of the lock is made by xchg or similar atomic operations ).

How to calculate the time it took to lock a mutex?

First off lets start with the simplest possible thing. On multiple threads run this loop: So we take a timestamp before we call lock and a timestamp after we have succeeded in locking the mutex. (or a spinlock. It’s a template) Then we remember the longest time it took.

Is it safe to use a spinlock on a single CPU?

Using spinlocks on a single-core/single-CPU system makes usually no sense, since as long as the spinlock polling is blocking the only available CPU core, no other thread can run and since no other thread can run, the lock won’t be unlocked either. IOW, a spinlock wastes only CPU time on those systems for no real benefit.