What is 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.
Can you use Pthread in C++?
In a Unix/Linux operating system, the C/C++ languages provide the POSIX thread(pthread) standard API(Application program Interface) for all thread related functions. It allows us to create multiple threads for concurrent process flow.
What is a condition variable in C++?
Condition variable. A condition variable is an object able to block the calling thread until notified to resume. It uses a unique_lock (over a mutex ) to lock the thread when one of its wait functions is called.
How do you create a condition variable?
A condition variable is created by calling the pthread_cond_init subroutine. You may specify a condition attributes object. If you specify a NULL pointer, the condition variable will have the default attributes.
How do you use condition variables?
Condition variables: used to wait for a particular condition to become true (e.g. characters in buffer). wait(condition, lock): release lock, put thread to sleep until condition is signaled; when thread wakes up again, re-acquire lock before returning.
Can we use pthread in Windows?
Windows does not support the pthreads standard natively, therefore the Pthreads4w project seeks to provide a portable and open-source wrapper implementation. It can also be used to port Unix software (which uses pthreads) with little or no modification to the Windows platform.
What is a condition on a variable?
An equation is a condition on a variable. It is expressed by saying that an expression with a variable is equal to a fixed number, e.g. x – 3 = 10.
What is the condition of a variable?
A condition variable indicates an event and has no value. More precisely, one cannot store a value into nor retrieve a value from a condition variable. If a thread must wait for an event to occur, that thread waits on the corresponding condition variable.
Should condition variables be used with pthread_cond_wait?
it appears that a condition variable only works if pthread_cond_wait is called before the other thread calls pthread_cond_notify. If notify somehow happens before wait then wait will be stuck. My question is: when should condition variables be used? The scheduler can preempt threads and a notify may happen before wait.
What is the use of conditional variable in threading?
Conditional variables are useful in cases where you want a thread to wait for something that happens in another thread. For instance, in a producer/consumer scenario with one or or more producing threads and one consuming thread, conditional variables can be used to signal the consuming thread that new data is available.
When to use pthread_cond_broadcast (3thr)?
Use pthread_cond_broadcast(3THR) to unblock all threads that are blocked on the condition variable pointed to by cv, specified by pthread_cond_wait(). When no threads are blocked on the condition variable, pthread_cond_broadcast() has no effect.
What happens when pthread_cond_init returns zero?
If a condition variable is reinitialized or destroyed, the application must be sure the condition variable is not in use. Return Values pthread_cond_init()returns zero after completing successfully. Any other returned value indicates that an error occurred.
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