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Is a mutex lock a spin lock?
A hybrid mutex behaves like a spinlock at first on a multi-core system. 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.
Does a mutex wait?
If a mutex is unlocked and you call wait then the call does nothing (it does not wait) and the thread continues its execution. When a mutex is locked and you call wait then the thread is blocked. When other thread calls unlock then blocking is released and the mutex becomes unlocked.
How slow is a mutex?
The following code demonstrates the cost of calling mutexes, atomic operations, and also the inline template. So the mutex calls are about 3x slower than atomic operations. Calling libc is about 10ns slower than using an inline template (not a bad difference in return for not having to write the inline template code).
What does a mutex lock do?
Mutexes are used to protect shared resources. If the mutex is already locked by another thread, the thread waits for the mutex to become available. The thread that has locked a mutex becomes its current owner and remains the owner until the same thread has unlocked it.
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. There are two ways to avoid this: Do not acquire the lock. Spinlocks that never entail switching, usable by real-time operating systems, are sometimes called raw spinlocks.
What’s the difference between mutex and spin lock?
Process will be busy in a loop till it gets the resource. So we get the first difference there itself, the way both wait for the resource lock. In case of mutex, process goes in wait state and does not use processor while in spin-lock, process keeps on looping and hence uses the processor even while waiting.
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 ).
What happens when a thread tries to lock a mutex?
In theory, when a thread tries to lock a mutex and it does not succeed, because the mutex is already locked, it will go to sleep, immediately allowing another thread to run. It will continue to sleep until being woken up, which will be the case once the mutex is being unlocked by whatever thread was holding the lock before.
Is there a problem with using a mutex?
The problem with mutexes is that putting threads to sleep and waking them up again are both rather expensive operations, they’ll need quite a lot of CPU instructions and thus also take some time.