What is read/write lock Pthread?

What is read/write lock Pthread?

Write Lock on Read-Write Lock #include . The calling thread acquires the write lock if no other thread (reader or writer) holds the read-write lock rwlock. Otherwise, the thread blocks (that is, does not return from the pthread_rwlock_wrlock() call) until it can acquire the lock.

How do you use Reader writer lock?

Instead of having a single lock method, they have two – one for readers and one for writers. When readers enter the critical section they invoke the reader lock (and then reader unlock on exit); when writers enter the critical section they invoke the writer lock (and then writer unlock on exit).

What is Pthread_mutex?

int pthread_mutex_lock(pthread_mutex_t *mutex) : Locks a mutex object, which identifies a mutex. The thread that has locked a mutex becomes its current owner and remains the owner until the same thread has unlocked it. When the mutex has the attribute of recursive, the use of the lock may be different.

Can 2 threads read the same variable?

No this operation is not inherently thread safe. Even though the variable is not currently being written to, previous writes to the variable may not yet be visible to all threads. This means two threads can read the same value and get different results creating a race condition.

What happens when mutex is locked?

Locks a mutex object, which identifies a mutex. 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 overhead of locking?

lock overhead: the extra resources for using locks, like the memory space allocated for locks, the CPU time to initialize and destroy locks, and the time for acquiring or releasing locks.

When to use reader writer lock in C #?

Use Reader-Writer Lock in C#. March 7, 2016 1. It is safe to let multiple threads read the data at the same time, but when a thread needs to write, all other threads need to be blocked. .NET originally provided the ReaderWriterLock for this situation, but it has performance problems.

Is there a slim reader / writer lock in C + + 17?

It also introduces the Slim reader/writer lock, a kernel synchronisation primitive introduced with Vista. There’s also a CodeProject article about comparing different implementations (including the MSDN article’s ones). C++17 supports std::shared_mutex .

How does Wlock work when there are no readers?

Here’s a simple, though inefficient, way to do this: The writer locks the mutex and checks if there are readers inside the lock. If there are, it releases the mutex and tries again – this is called spinning . If there are no readers, WLock returns with the mutex still locked, so readers won’t be able to take the lock.

Where is the readerwriterlock declared in the class?

Note that the ReaderWriterLock is declared at the class level so that it is visible to all threads. // This example shows a ReaderWriterLock protecting a shared // resource that is read concurrently and written exclusively // by multiple threads.