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semaphore.cpp
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semaphore.cpp
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#include <iostream>
#include <string>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <vector>
class Semaphore {
std::condition_variable cv;
std::mutex mtx;
int value;
public:
Semaphore(int initial_value): value(initial_value) {}
int up() {
std::lock_guard<std::mutex> lock(mtx);
if (++value > 0)
cv.notify_one();
return value;
}
int down() {
std::unique_lock<std::mutex> lock(mtx);
while (value <= 0) {
cv.wait(lock);
}
if (--value > 0) {
cv.notify_one();
}
return value;
}
};
Semaphore s(10);
void thread_func(unsigned int id)
{
for (int i = 0; i < 10000; ++i) {
printf("%d\n", s.down());
sched_yield();
printf("%d\n", s.up());
}
}
int main (int argc, char* argv[])
{
int n = 20;
std::vector <std::thread> threads(n);
for (int i = 0; i < n; ++i) {
threads[i] = std::thread(thread_func, i);
}
for (int i = 0; i < n; ++i) {
threads[i].join();
}
return 0;
}