Can thread wait in multiple condition variables?
You can’t, and must redesign. One thread may wait on only one condition variable (and its associated mutex) at a time.
What does Pthread cond wait do?
The pthread_cond_wait() function blocks the calling thread, waiting for the condition specified by cond to be signaled or broadcast to. When pthread_cond_wait() is called, the calling thread must have mutex locked.
How do you make Pthread wait?
The waiting on other threads is accomplished by using the function pthread_join() (more later). Joinable threads may call pthread_join() to wait on another thread. The default value is joinable, you do NOT want to change this (unless you are going to provide some kind of barrier synchronization routine yourself….)
How does the conditional variable prevent the threads from continuously waiting for the thread?
Condition variables support operations that “wake one” or “wake all” waiting threads. After a thread is woken, it re-acquires the lock it released when the thread entered the sleeping state.
Is pthread_cond_signal thread safe?
It is not safe to use the pthread_cond_signal() function in a signal handler that is invoked asynchronously. Even if it were safe, there would still be a race between the test of the Boolean pthread_cond_wait() that could not be efficiently eliminated.
Why do we need to use conditional variables in pthread with a mutex lock?
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. The wait will “atomically” unlock the mutex, allowing others access to the condition variable (for signalling).
How does condition variable Wait work?
When a thread gets signaled by a condition variable, it will return from wait() . But not immediately, it must wait until the thread locks the mutex again, however long it takes. It will not go “back to sleep”, but wait until it has the mutex locked again, and then return.
Is condition variable busy wait?
Comparing them line by line, condition variable replaces the “busy wait” loop and inspects the same predicate that stops the loop (g_ready). The combination of mutex + condition_variable + shared global state is useful when conducting inter-thread communication.
Why do we need to use conditional variables in Pthread with a mutex lock?
How does the conditional variable prevent the threads from continuously waiting for the thread select the correct statements that answer the above mentioned question?
answer: a)The solution makes threads to check a condition and if that condition is true, then the threads go to sleep. When the threads go to sleep, they execute the wait() operation. When the thread using the lock releases it, then it notifies all the threads in the waiting queue.
Does pthread_cond_signal unlock mutex?
The pthread_cond_signal() routine is used to signal (or wake up) another thread which is waiting on the condition variable. It should be called after mutex is locked, and must unlock mutex in order for pthread_cond_wait() routine to complete.
Does pthread_cond_signal release lock?
No, it doesn’t unlock any mutex at all.
Does pthread_mutex_lock wait?
When pthread_cond_wait blocks (that is needs to wait) it releases the mutex. In other words, pthread_cond_wait is not blocked on the mutex so unlocking the mutex has no affect on the thread calling pthread_cond_wait . In fact, it is recommended but not required for the pthread_cond_signal caller to lock the mutex.
Why wait () and signal () operations should execute atomically?
If two wait operations are executed on a semaphore when its value is 1, if the two operations are not performed atomically, then it is possible that both operations might proceed to decrement the semaphore value, thereby violating mutual exclusion.
Does condition variable wait release lock?
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.