What is the conditional variable in Pthread?

What is the conditional variable in Pthread?

Along with mutexes, pthreads gives us another tool for synchronization between the threads, condition variables. Condition variables are variables of the kind pthread_cond_t. When a thread is waiting on a mutex it will continuously keep polling on the mutex waiting for it to get unlocked.

Why do we need to use conditional variables in Pthread with a mutex lock?

10 Answers. It’s just the way that condition variables are (or were originally) implemented. The mutex is used to protect the condition variable itself. That’s why you need it locked before you do a wait.

How do you initialize a condition variable?

The pthread_cond_init() function shall initialize the condition variable referenced by cond with attributes referenced by attr. If attr is NULL, the default condition variable attributes shall be used; the effect is the same as passing the address of a default condition variable attributes object.

Is mutex a condition variable?

Mutex is for exclusive access of shared resources, while conditional variable is about waiting for a condition to be true. Both are different kernel resources.

What is Pthread barrier?

A barrier is a point where the thread is going to wait for other threads and will proceed further only when predefined number of threads reach the same barrier in their respective programs. To use a barrier we need to use variables of the type pthread_barrier_t.

Which of the following type of lock can be used to create a condition variable?

To wait on an explicit lock, you create a condition variable (an object that supports the Condition interface) using the Lock.

How do you initialize mutex?

A mutex can be statically initialized by assigning PTHREAD_MUTEX_INITIALIZER in its definition, as follows: pthread_mutex_t def_mutex = PTHREAD_MUTEX_INITIALIZER; A mutex must be initialized (either by calling pthread_mutex_init(), or statically) before it may be used in any other mutex functions.

What is mutex condition?

5 Mutexes and Condition Variables. Short for “mutual exclusion”, the name “mutex” indicates that only one thread at a time can acquire access to data that is protected by a mutex – threads are excluded from accessing data at the same time.

What is mutex variable?

Mutex variables are one of the primary means of implementing thread synchronization and for protecting shared data when multiple writes occur. A mutex variable acts like a “lock” protecting access to a shared data resource. No other thread can own that mutex until the owning thread unlocks that mutex.

How do you use Pthread barriers?

Barrier Pthread Example: Ladies First!

1. We have 2 man pthreads and 1 woman pthread.
2. The men will wait until the woman has eaten. Implicitly, the men pthreads must start before the woman.
3. Once the woman has eaten the men are free to eat.
4. Men will eat and the program will end.

How does pthread _ mutex _ lock ( ) work?

A mutex is locked using pthread_mutex_lock (). cond is a condition variable that is shared by threads. To change it, a thread must hold the mutex associated with the condition variable. The pthread_cond_wait () function releases this mutex before suspending the thread and obtains it again before returning.

Which is an example of using pthread’s condition variables?

An example of using pthread’s condition variables, showing how to block a main thread while waiting for worker threads to finish their work, without joining the threads. This could be useful if you want to loop the threads, for example.

Can you use condition variables without a mutex?

If you think you can use condition variables without a mutex, then you haven’t grasped that condition variables are stateless. Condition variables are built around a condition. Threads that wait on a condition variable are waiting for some condition. Threads that signal condition variables change that condition.

Why does pthread _ cond _ wait cause a wait?

This causes one or all of the threads waiting on the condition to unblock and to try to acquire the mutex lock again. Because the condition can change before an awakened thread returns from pthread_cond_wait(), the condition that caused the wait must be retested before the mutex lock is acquired.