C++ thread and mutex and condition variable - multithreading

Question

findsmallest common multiple of 10-million numbers in the queue does not exceed 10,000
I killed 2 days to sort out but I just do not understand! please help me
#include <condition_variable>
#include <mutex>
#include <thread>
#include <iostream>
#include <queue>
#include <chrono>
#include <cmath>
#include <map>
#include <cstdlib>
#include <fstream>
#include <ctime>
using namespace std;
int main()
{
std::map <int, int> NOK;
map<int, int> snok;
std::queue<int> oche;
std::mutex m;
std::condition_variable cond_var;
bool done = false;
bool notified = false;
std::thread filev([&]() {
//std::unique_lock<std::mutex> lock(m);
ifstream in; // Поток in будем использовать для чтения
int ch;
in.open("/home/akrasikov/prog/output.txt");
while(!in.eof()){
if (oche.size()>9999){
std::this_thread::sleep_for(std::chrono::milliseconds(3));
std::unique_lock<std::mutex> lock(m);
} else {
in>>ch;
oche.push(ch);
}
}
notified = true;
cond_var.notify_one();
done = true;
cond_var.notify_one();
});
std::thread nok([&]() {
std::unique_lock<std::mutex> lock(m);
while (!done) {
while (!notified) { // loop to avoid spurious wakeups
cond_var.wait(lock);
}
while (!oche.empty()) {
ch=oche.front();
oche.pop();
int j=2;
while (j < sqrt((double)ch)+1){
int s=0;
while(!(ch%j)){
s++;
ch/=j;
}
if (s > 0 && NOK[j] < s){
NOK[j] = s;
}
j++;
}
if (NOK[ch] == 0) NOK[ch]++;
}
long int su=1;
int temp=-1;
int step=0;
int sa=1;
std::cout << " NOK= ";
for (std::map<int, int>::iterator it=NOK.begin(); it!=NOK.end(); it++){
for (int i=0; i<it->second; i++){
su*=it->first;
sa=it->first;
if (temp<sa && sa >1){
temp=sa;
step=1;
} else {
if(sa>1)
step++;
}
}
cout<< temp << "^"<< step << " * " ;
}
std::cout << "su = " << su << '\n';
}
notified = false;
});
filev.join();
nok.join();
}
This program does not work! how come? what's wrong? it just starts and hangs, but if you do not delete is code
if (oche.size()>9999){
std::this_thread::sleep_for(std::chrono::milliseconds(3));
std::unique_lock<std::mutex> lock(m);
} else {
and
while (!done) {
while (!notified) { // loop to avoid spurious wakeups
cond_var.wait(lock);
}
everything works help plz

Answer 1

From what I understand of your problem, you have 3 problems
Conpute the least common multiple for a list of 1M elements
You want to have one thread that produces the elements and one that consumes it. They transfer it through a buffer (a queue in your case)
Your queue cannot exceed 10K elements
In my implementation I m generating the numbers randomly and using condition variables to coordinate between the threads.
Note that the LCM is associative so you can compute it recursively, not matter what the order is.
Here is the code but please DO NOT POST DIRTY CODE LIKE YOU DID NEXT TIME OR EVERYONE will kick you out.
Here is the code
#include <condition_variable>
#include <mutex>
#include <thread>
#include <iostream>
#include <queue>
#include <chrono>
#include <cmath>
#include <map>
#include <cstdlib>
#include <fstream>
#include <ctime>
#include <atomic>
#include <random>
using namespace std;
std::mutex mutRandom;//use for multithreading for random variables
int getNextRandom()
{
std::lock_guard<std::mutex> lock(mutRandom);
// C++11 Random number generator
std::mt19937 eng (time(NULL)); // Mersenne Twister generator with a different seed at each run
std::uniform_int_distribution<int> dist (1, 1000000);
return dist(eng);
}
//thread coordination
std::mutex mut;
std::queue<int> data_queue;
std::condition_variable data_cond;
std::atomic<int> nbData=0;
std::atomic<int> currLCM=1;//current LCM
const unsigned int nbMaxData=100000;
const unsigned int queueMaxSize=10000;
//Arithmetic function, nothing to do with threads
//greatest common divider
int gcd(int a, int b)
{
for (;;)
{
if (a == 0) return b;
b %= a;
if (b == 0) return a;
a %= b;
}
}
//least common multiple
int lcm(int a, int b)
{
int temp = gcd(a, b);
return temp ? (a / temp * b) : 0;
}
/// Thread related part
//for producing the data
void produceData()
{
while (nbData<nbMaxData)
{
std::unique_lock<std::mutex> lk(mut);
data_cond.wait(lk,[]{
return data_queue.size()<queueMaxSize;
});
cout<<nbData<<endl;
++nbData;
data_queue.push(getNextRandom());
data_cond.notify_one();
lk.unlock();
}
cout<<"Producer done \n";
}
//for consuming the data
void consumeData()
{
while (nbData<nbMaxData)
{
std::unique_lock<std::mutex> lk(mut);
data_cond.wait(lk,[]{
return !data_queue.empty();
});
int currData=data_queue.front();
data_queue.pop();
lk.unlock();
currLCM = lcm(currLCM,currData);
}
cout<<"Consumer done \n";
}
int main()
{
std::thread thProduce(&produceData);
std::thread thConsume(&consumeData);
thProduce.join();//to wait for the producing thread to finish before the program closes
thConsume.join();//same thing for the consuming one
return 0;
}
Hope that helps,