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