What is a mutex deadlock?

Mutexes provide a mechanism for allowing one thread to block the execution of another. This opens up the possibility of a new class of bugs, called deadlocks. A deadlock occurs when one or more threads are stuck waiting for something that never will occur.

Can mutex lead to deadlock?

Locking a fast mutex (the default kind) will cause a deadlock to occur. An attempt to lock the mutex blocks until the mutex is unlocked. But because the thread that locked the mutex is blocked on the same mutex, the lock cannot ever be released. Locking a recursive mutex does not cause a deadlock.

How can we avoid mutex deadlock?

One of the most common ways of avoiding a deadlock is to always lock the two mutexes in the same order. If we always lock mutex A before mutex B, then we’ll never have a deadlock.

How do you detect a mutex deadlock?

To detect deadlock between threads, we need to track blocked threads and the mutexes they are blocked on, as well as be able to easily find the owner of a given mutex. This information needs to be updated every time a mutex lock is attempted (whether it succeeds or not).

How do you avoid deadlocks?

How To Avoid Deadlock

1. Avoid Nested Locks: A deadlock mainly happens when we give locks to multiple threads. Avoid giving a lock to multiple threads if we already have given to one.
2. Avoid Unnecessary Locks: We can have a lock only those members which are required.
3. Using Thread.

How deadlock can occur when mutex locks are used?

Deadlock is possible if thread1 acquires mutex1 while thread2 acquires mutex2. Even though deadlock is possible, it will not occur if thread1 can acquire and release the mutex locks for mutex1 and mutex2 before thread2 tries to acquire the locks. Of course, CPU scheduler scheduled the order in which the threads run.

How can we remove deadlock?

Deadlock can be prevented by eliminating any of the four necessary conditions, which are mutual exclusion, hold and wait, no preemption, and circular wait. Mutual exclusion, hold and wait and no preemption cannot be violated practically.

How do you avoid deadlock?

Deadlock can be prevented by eliminating any of the four necessary conditions, which are mutual exclusion, hold and wait, no preemption, and circular wait. Mutual exclusion, hold and wait and no preemption cannot be violated practically. Circular wait can be feasibly eliminated by assigning a priority to each resource.

Is a mutex a 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).

What is a mutex thread?

Mutex is a synchronization primitive that grants exclusive access to the shared resource to only one thread. If a thread acquires a mutex, the second thread that wants to acquire that mutex is suspended until the first thread releases the mutex.

What are the types of deadlocks?

Two types of deadlocks can be considered:

• Resource Deadlock. Occurs when processes are trying to get exclusive access to devices, files, locks, servers, or other resources.
• Communication Deadlock.

What are mutex?

In computer programming, a mutex (mutual exclusion object) is a program object that is created so that multiple program thread can take turns sharing the same resource, such as access to a file.

How to avoid deadlock when using mutex?

There are many techniques that allow us to avoid the deadlocks. The simplest solution is to always lock the mutexes in the same order. The std::lock function can lock 2 or more mutexes at once without risk of a deadlock.

What happens when a thread tries to acquire a locked mutex?

If a thread try to acquire a locked mutex, the call to pthread_mutex_lock () blocks the thread until the owner of the mutex lock invokes pthread_mutex_unlock (). Let’s take an example, two Mutex locks are created in the following Code −

Which function locks the mutex associated with the bag?

The thread t1 runs the function makeAppleJuice and locks the mutex associated with printing. At the same time, the thread t2 runs the function throwOutPear an it locks the mutex associated with the bag. At this point in time, both mutexes are locked.

How do you lock mutexes in the same order?

Don’t lock a mutex if you already locked another mutex. If you need to do it, do it with std::lock. Generalization of locking the mutexes in the same order is to have a hierarchy of mutexes. Then you only lock a mutex if it is high/low enough in the hierarchy. We explored two problems regarding mutexes: forgetting to unlock and having a deadlock.