Do condition variables need a mutex?
Not all condition variable functions require a mutex: only the waiting operations do. The signal and broadcast operations do not require a mutex. A condition variable also is not permanently associated with a specific mutex; the external mutex does not protect the condition variable.
Why do I need condition variables can’t I just use mutex lock for all synchronization problems?
A mutex might have several related condition variables. And you need condition variables because such conditions may not always be expressed as simply as “a mutex is locked” (so you need to broadcast changes in conditions to other threads).
How are condition variables implemented?
The implementation of condition variables involves several mutexes. Condition variables support three operations: wait – add calling thread to the queue and put it to sleep. broadcast – remove and wake-up all threads on the queue.
What’s the difference between mutex and condition variable?
A monitor (a mutex + a conditional variable) helps us here. We still need a mutex to guarantee mutual exclusive access but a conditional variable lets us sleep and wait for a certain condition. The condition here is the producer adding an item to the buffer.
How do you mutex a variable?
A typical sequence in the use of a mutex is as follows:
- Create and initialize a mutex variable.
- Several threads attempt to lock the mutex.
- Only one succeeds and that thread owns the mutex.
- The owner thread performs some set of actions.
- The owner unlocks the mutex.
- Another thread acquires the mutex and repeats the process.
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.
Why are condition variables needed?
Condition variables are used to wait until a particular condition predicate becomes true. This condition predicate is set by another thread, usually the one that signals the condition. A condition predicate must be protected by a mutex.
What are the two operations that can be performed on a condition variable?
There are only two operations that can be applied to a condition variable: wait and signal.
What is conditional mutex?
std::condition_variable The wait operations atomically release the mutex and suspend the execution of the thread. When the condition variable is notified, a timeout expires, or a spurious wakeup occurs, the thread is awakened, and the mutex is atomically reacquired.
Is condition variable same as semaphore?
semaphore and condition variables are very similar and are used mostly for the same purposes. However, there are minor differences that could make one preferable. For example, to implement barrier synchronization you would not be able to use a semaphore. But a condition variable is ideal.
How do I wait for an event with a mutex?
Use the condition_variable class to wait for an event when you have a mutex of type unique_lock . Objects of this type may have better performance than objects of type condition_variable_any >.
How to associate a mutex with the internal state of the buffer?
We can associate a mutex with the internal state of the buffer, and only access these internal state when the mutex is locked. The bounded_buffer::write () method in synch2/bbuffer-mutex.cc is implemented with mutex synchronization.
What is the relationship between a mutex and the state it protects?
The association between the mutex and the state it protects is rather arbitrary. These mutexes are also called “advisory locks”, as their association with the state they protect are not enforced in any way by the runtime system, and must be taken care of by the programmer.
How effective are mutexes?
Their effectiveness solely relies on the program following protocols associating the mutex with the protected state. In other words, if a mutex is not used correctly, there is no guarantee that the underlying state is being properly protected.