Part 1 Read the code in example1.cpp. It creates four threads: two to run the function doit and the other two to run a function object. The four threads run concurrently with two threads run doit() incrementing/decrementing the global variable _y_ and two threads run function objects incrementing/decrementing the local variable _x_. From the output you can see that there is data corruption since both _x_ and _y_ should be 0. To fix this problem uncomment the line with ``` #define SYNC ```. ### Question We learned that a mutex _m_ is locked with a wait(m), (in C++ it is ``` m.lock() ```) and unlocked with signal(m) (in C++ it is ``` m.unlock() ```). How is this done in example.cpp? What is a ``` lock_guard ``` ? Write your answer here by editing this file (no more that a few lines)

#### Answer

Write your answer here

example.cpp:

#include #include #include #include

//uncomment line below to get correct result //#define SYNC int y = 0; int num_iterations = 100000; int num_trials=10; std::mutex m; #define INC 1 #define DEC -1 int gcd(int a,int b) { if (b == 0) return a; return gcd(b, a % b); } void doit(int a, int b,int op) { for (int i = 0; i < num_iterations; i++) { gcd(a, b); #ifdef SYNC std::lock_guard g(m); #endif op>=0?y++:y--;

} } class funcObject { int& _x; int _a, _b, _op; public: funcObject(int& x, int a, int b,int op) :_x(x), _a(a), _b(b),_op(op) {} void operator() () { for (int i = 0; i g(m); #endif _op>=0?_x++:_x--; }

} };

int main() { int a, b; std::default_random_engine e; std::uniform_int_distribution id(100000, 1000000); a = id(e); b = id(e); for (int j = 0; j mythreads; int x = 0; y = 0; funcObject c(x, a, b,INC); std::thread t1(c); std::thread t2(doit, a, b,INC); /* below will not work because a vector will attempt to make a copy of t1 and t2 and the copy constructor for the thread class is deleted mythreads.push_back(t1); mythreads.push_back(t2); */ mythreads.push_back(std::move(t1)); mythreads.push_back(std::move(t2)); mythreads.push_back( std::thread(funcObject(x,a,b,DEC))); mythreads.push_back( std::thread(doit, a, b,DEC)); for (auto& t : mythreads) t.join(); std::cout << "trial " << j << ",x=" << x << ",y=" <

}

}