1 #include <chrono>
2 #include <condition_variable>
3 #include <cstdio>
4 #include <random>
5 #include <thread>
6
7 std::default_random_engine g_random_engine{std::random_device{}()};
8 std::uniform_int_distribution<> g_distribution{0, 3000000};
9 std::condition_variable g_condition_variable;
10 std::mutex g_mutex;
11 int g_count;
12
13 char *g_char_ptr = nullptr;
14
15 void
barrier_wait()16 barrier_wait()
17 {
18 std::unique_lock<std::mutex> lock{g_mutex};
19 if (--g_count > 0)
20 g_condition_variable.wait(lock);
21 else
22 g_condition_variable.notify_all();
23 }
24
25 void
do_bad_thing_with_location(char * char_ptr,char new_val)26 do_bad_thing_with_location(char *char_ptr, char new_val)
27 {
28 *char_ptr = new_val;
29 }
30
31 uint32_t
access_pool(bool flag=false)32 access_pool (bool flag = false)
33 {
34 static std::mutex g_access_mutex;
35 if (!flag)
36 g_access_mutex.lock();
37
38 char old_val = *g_char_ptr;
39 if (flag)
40 do_bad_thing_with_location(g_char_ptr, old_val + 1);
41
42 if (!flag)
43 g_access_mutex.unlock();
44 return *g_char_ptr;
45 }
46
47 void
thread_func(uint32_t thread_index)48 thread_func (uint32_t thread_index)
49 {
50 printf ("%s (thread index = %u) startng...\n", __FUNCTION__, thread_index);
51
52 barrier_wait();
53
54 uint32_t count = 0;
55 uint32_t val;
56 while (count++ < 15)
57 {
58 // random micro second sleep from zero to 3 seconds
59 int usec = g_distribution(g_random_engine);
60 printf ("%s (thread = %u) doing a usleep (%d)...\n", __FUNCTION__, thread_index, usec);
61 std::this_thread::sleep_for(std::chrono::microseconds{usec});
62
63 if (count < 7)
64 val = access_pool ();
65 else
66 val = access_pool (true);
67
68 printf ("%s (thread = %u) after usleep access_pool returns %d (count=%d)...\n", __FUNCTION__, thread_index, val, count);
69 }
70 printf ("%s (thread index = %u) exiting...\n", __FUNCTION__, thread_index);
71 }
72
73
main(int argc,char const * argv[])74 int main (int argc, char const *argv[])
75 {
76 g_count = 4;
77 std::thread threads[3];
78
79 g_char_ptr = new char{};
80
81 // Create 3 threads
82 for (auto &thread : threads)
83 thread = std::thread{thread_func, std::distance(threads, &thread)};
84
85 printf ("Before turning all three threads loose...\n"); // Set break point at this line.
86 barrier_wait();
87
88 // Join all of our threads
89 for (auto &thread : threads)
90 thread.join();
91
92 delete g_char_ptr;
93
94 return 0;
95 }
96