Is STD mutex reentrant?
Can std::mutex be reentrant? No, but if you want a recursive mutex, the std::recursive_mutex class provides that functionality.
What is a non recursive mutex?
Because the recursive mutex has a sense of ownership, the thread that grabs the mutex must be the same thread that releases the mutex. In the case of non-recursive mutexes, there is no sense of ownership and any thread can usually release the mutex no matter which thread originally took the mutex.
Why are recursive mutexes bad?
Using recursive mutexes encourages you to not think your concurrency design clearly. There is no long term benefit in using recursive mutexes. Recursive mutexes are technical debt.
What is the 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.
What is a reentrant lock?
What Is a Reentrant Lock? A reentrant lock is a mutual exclusion mechanism that allows threads to reenter into a lock on a resource (multiple times) without a deadlock situation. A thread entering into the lock increases the hold count by one every time. Similarly, the hold count decreases when unlock is requested.
What is the difference between unique_lock and Lock_guard?
A lock_guard always holds a lock from its construction to its destruction. A unique_lock can be created without immediately locking, can unlock at any point in its existence, and can transfer ownership of the lock from one instance to another.
What will happen if a non recursive mutex is locked?
What happens if a non-recursive mutex is locked more than once. Deadlock. If a thread that had already locked a mutex, tries to lock the mutex again, it will enter into the waiting list of that mutex, which results in a deadlock.
Is std :: mutex slow?
TLDR; The 2015 MSVC C++ runtime’s std::mutex (and potentially other) implementation is significantly slower than the equivalent code written by hand. The reason is that the runtime is built with a Windows feature called “Control Flow Guard” and uses function pointers.
When should you use a spinlock?
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.
Does unique_lock automatically unlock?
The std::scoped_lock and std::unique_lock objects automate some aspects of locking, because they are capable of automatically unlocking.
What is unique_lock mutex?
The class unique_lock is a general-purpose mutex ownership wrapper allowing deferred locking, time-constrained attempts at locking, recursive locking, transfer of lock ownership, and use with condition variables.
What is the difference between Unique_lock and Lock_guard?
Are mutexes expensive?
Some mutexes will cost almost nothing if there is native hardware support, others will cost a lot. It’s impossible to answer without more information.
When should you spinlock?
The rule for using spinlocks is simple: use a spinlock if and only if the real time the lock is held is bounded and sufficiently small. Note that usually user implemented spinlocks DO NOT satisfy this requirement because they do not disable interrupts.
What is the main disadvantage of spinlock?
The primary disadvantage of a spinlock is that, while waiting to acquire a lock, it wastes time that might be productively spent elsewhere.