update

Threading_In_CPlusPlus/4.mutex/critical_section.cpp

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+//
+// Created by light on 20-2-1.
+//
+#include <iostream>
+#include <mutex>
+#include <thread>
+
+using namespace std;
+
+int sum = 0; //shared
+
+mutex m;
+
+void *countgold() {
+    int i; //local to each thread
+    for (i = 0; i < 10000000; i++) {
+        m.lock();
+        sum += 1;
+        m.unlock();
+    }
+    return NULL;
+}
+
+int main() {
+    thread t1(countgold);
+    thread t2(countgold);
+
+    //Wait for both threads to finish
+    t1.join();
+    t2.join();
+
+    cout << "sum = " << sum << endl;
+    return 0;
+}