1 files changed, 75 insertions, 0 deletions
diff --git a/store/works/life/operating-system-experiment/ParallelCalculationDemo.cpp b/store/works/life/operating-system-experiment/ParallelCalculationDemo.cpp
new file mode 100644
index 0000000..0174c55
--- /dev/null
+++ b/store/works/life/operating-system-experiment/ParallelCalculationDemo.cpp
@@ -0,0 +1,75 @@
+#include "Thread.h"
+
+#include <iostream>
+
+const long long N = 1e9;
+
+int main(int argc, char **argv) {
+  int thread_number;
+  if (argc == 1) {
+    thread_number = 1;
+  } else if (argc == 2) {
+    thread_number = std::atoi(argv[1]);
+    if (thread_number <= 0) {
+      std::cerr << "Argument must be a positive integer.\n";
+      return -1;
+    }
+  } else {
+    std::cerr << "Too many arguments.\n";
+    return -1;
+  }
+
+  std::cout << "Use " << thread_number << " threads to calculate sum of 1-" << N
+            << ".\n";
+
+  if (thread_number == 1) {
+    long long sum = 0;
+    for (long long i = 1; i <= 1e9; i++) {
+      sum += i;
+    }
+    std::cout << "Sum of 1-" << N << " is " << sum << '\n';
+  } else {
+    std::vector<cru::Thread> threads(thread_number);
+    std::vector<long long> partial_sum(thread_number);
+
+    long long step = N / thread_number;
+
+    for (int i = 0; i < thread_number; i++) {
+      long long start = step * i;
+      long long end = step * (i + 1);
+
+      long long &ps = partial_sum[i];
+
+      if (i == thread_number - 1) {
+        threads[i] = cru::Thread([&ps, start] {
+          long long sum = 0;
+          for (long long j = start; j <= N; j++) {
+            sum += j;
+          }
+          ps = sum;
+        });
+      } else {
+        threads[i] = cru::Thread([&ps, start, end] {
+          long long sum = 0;
+          for (int j = start; j < end; j++) {
+            sum += j;
+          }
+          ps = sum;
+        });
+      }
+    }
+
+    for (auto &thread : threads) {
+      thread.Join();
+    }
+
+    long long sum = 0;
+    for (auto ps : partial_sum) {
+      sum += ps;
+    }
+
+    std::cout << "Sum of 1-" << N << " is " << sum << '\n';
+  }
+
+  return 0;
+}