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...