Example solution for C++ 101 Exercise 4 (threads and task runners)

base/cpp101/factor.cc

Index: base/cpp101/factor.cc
diff --git a/base/cpp101/factor.cc b/base/cpp101/factor.cc
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+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdio.h>
+
+#include "base/at_exit.h"
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/callback.h"
+#include "base/location.h"
+#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/task_runner.h"
+#include "base/threading/thread.h"
+#include "base/time/time.h"
+
+namespace {
+
+bool FindNonTrivialFactor(int n, int* factor) {
+  // Really naive algorithm.
+  for (int i = 2; i < n; ++i) {
+    if (n % i == 0) {
+      *factor = i;
+      return true;
+    }
+  }
+  return false;
+}
+
+void FindNonTrivialFactorHelper(int n, int* factor, bool* found) {
+  *found = FindNonTrivialFactor(n, factor);
+}
+
+void PrintStatusUpdate(base::Time start_time) {
+  double num_seconds = (base::Time::Now() - start_time).InSecondsF();
+  printf("Waited for %f seconds...\n", num_seconds);
+}
+
+void PrintStatusUpdateRepeatedly(
+    const scoped_refptr<base::TaskRunner>& task_runner,
+    base::Time start_time,
+    base::TimeDelta print_interval) {
+  PrintStatusUpdate(start_time);
+  task_runner->PostDelayedTask(FROM_HERE,
+                               base::Bind(PrintStatusUpdateRepeatedly,
+                                          task_runner,
+                                          start_time,
+                                          print_interval),
+                               print_interval);
+}
+
+}  // namespace
+
+int main(int argc, char* argv[]) {
+  base::AtExitManager exit_manager;
+
+  if (argc <= 1) {
+    printf("%s: missing operand\n", argv[0]);
+    return -1;
+  }
+
+  int n = 0;
+  if (!base::StringToInt(argv[1], &n) || n < 2) {
+    printf("%s: invalid n `%s'\n", argv[0], argv[1]);
+    return -1;
+  }
+
+  base::Thread worker_thread("Worker thread");
+  CHECK(worker_thread.Start());
+
+  base::MessageLoop main_loop;
+
+  base::RunLoop run_loop;
+
+  int factor = 0;
+  bool found = false;
+  worker_thread.message_loop_proxy()->PostTaskAndReply(
+      FROM_HERE,
+      base::Bind(&FindNonTrivialFactorHelper, n, &factor, &found),
+      run_loop.QuitClosure());
+
+  PrintStatusUpdateRepeatedly(main_loop.message_loop_proxy(),
+                              base::Time::Now(),
+                              base::TimeDelta::FromSeconds(1));
+
+  run_loop.Run();
+
+  worker_thread.Stop();
+
+  if (found) {
+    printf("found non-trivial factor %d for %d\n", factor, n);
+    DCHECK_EQ(n % factor, 0);
+  } else {
+    printf("%d is prime\n", n);
+  }
+
+  return 0;
+}