1 #include "pseudo_barrier.h"
2 #include "thread.h"
3 #include <atomic>
4 #include <chrono>
5 #include <cinttypes>
6 #include <csignal>
7 #include <cstdio>
8 #include <cstdlib>
9 #include <cstring>
10 #include <mutex>
11 #include <thread>
12 #include <unistd.h>
13 #include <vector>
14 
15 pseudo_barrier_t barrier;
16 std::mutex print_mutex;
17 std::atomic<bool> can_work = ATOMIC_VAR_INIT(false);
18 thread_local volatile sig_atomic_t can_exit_now = false;
19 
20 static void sigusr1_handler(int signo) {
21   std::lock_guard<std::mutex> lock{print_mutex};
22   std::printf("received SIGUSR1 on thread id: %" PRIx64 "\n", get_thread_id());
23   can_exit_now = true;
24 }
25 
26 static void thread_func() {
27   // this ensures that all threads start before we SIGSTOP
28   pseudo_barrier_wait(barrier);
29 
30   // wait till the main thread indicates that we can go
31   // (note: using a mutex here causes hang on FreeBSD when another thread
32   // is suspended)
33   while (!can_work.load())
34     std::this_thread::sleep_for(std::chrono::milliseconds(50));
35 
36   // the mutex guarantees that two writes don't get interspersed
37   {
38     std::lock_guard<std::mutex> lock{print_mutex};
39     std::printf("thread %" PRIx64 " running\n", get_thread_id());
40   }
41 
42   // give other threads a fair chance to run
43   for (int i = 0; i < 5; ++i) {
44     std::this_thread::yield();
45     std::this_thread::sleep_for(std::chrono::milliseconds(200));
46     if (can_exit_now)
47       return;
48   }
49 
50   // if we didn't get signaled, terminate the program explicitly.
51   _exit(0);
52 }
53 
54 int main(int argc, char **argv) {
55   int num = atoi(argv[1]);
56 
57   pseudo_barrier_init(barrier, num + 1);
58 
59   signal(SIGUSR1, sigusr1_handler);
60 
61   std::vector<std::thread> threads;
62   for (int i = 0; i < num; ++i)
63     threads.emplace_back(thread_func);
64 
65   // use the barrier to make sure all threads start before we SIGSTOP
66   pseudo_barrier_wait(barrier);
67   std::raise(SIGSTOP);
68 
69   // allow the threads to work
70   can_work.store(true);
71 
72   for (std::thread &thread : threads)
73     thread.join();
74   return 0;
75 }
76