Condition variable

In essence, a condition variable provides a mechanism through which a thread's execution can be controlled by another thread. This is done by having a shared variable which a thread will wait for until signaled by another thread. It is an essential part of the scheduler implementation we looked at in Chapter 4, Thread Synchronization and Communication.

For the C++11 API, condition variables and their associated functionality are defined in the <condition_variable> header.

The basic usage of a condition variable can be summarized from that scheduler's code in Chapter 4, Thread Synchronization and Communication.

 #include "abstract_request.h"

 #include <condition_variable>
 #include <mutex> 

using namespace std;


 class Worker {
    condition_variable cv;
    mutex mtx;
    unique_lock<mutex> ulock;
    AbstractRequest* request;
    bool running;
    bool ready;
    public:
    Worker() { running = true; ready = false; ulock = unique_lock<mutex...