Shared Variables
If more than one thread is sharing a variable, you have to coordinate the access. That’s the job for mutexes and locks in C++.
Data race
- A data race
- A data race is a state in which at least two threads access a shared data at the same time, and at least one of the threads is a writer. Therefore the program has undefined behaviour.
You can observe very well the interleaving of threads if a few threads write to std::cout. The output stream std::cout is, in this case, the shared variable.
std::cout// withoutMutex.cpp
...
#include <thread>...
using namespace std;
struct Worker{
Worker(string n):name(n){};
void operator() (){
for (int i= 1; i <= 3; ++i){
this_thread::sleep_for(chrono::milliseconds(200));
cout << name << ": " << "Work " << i << endl;
}
}
private:
string name;
};
thread herb= thread(Worker("Herb"));
thread andrei...