1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // UNSUPPORTED: libcpp-has-no-threads
10 
11 // <condition_variable>
12 
13 // class condition_variable;
14 
15 // void notify_one();
16 
17 #include <condition_variable>
18 #include <atomic>
19 #include <mutex>
20 #include <thread>
21 #include <cassert>
22 
23 #include "test_macros.h"
24 
25 
26 std::condition_variable cv;
27 std::mutex mut;
28 
29 std::atomic_int test1(0);
30 std::atomic_int test2(0);
31 std::atomic_int ready(2);
32 std::atomic_int which(0);
33 
34 void f1()
35 {
36   --ready;
37   std::unique_lock<std::mutex> lk(mut);
38   assert(test1 == 0);
39   while (test1 == 0)
40     cv.wait(lk);
41   which = 1;
42   assert(test1 == 1);
43   test1 = 2;
44 }
45 
46 void f2()
47 {
48   --ready;
49   std::unique_lock<std::mutex> lk(mut);
50   assert(test2 == 0);
51   while (test2 == 0)
52     cv.wait(lk);
53   which = 2;
54   assert(test2 == 1);
55   test2 = 2;
56 }
57 
58 int main(int, char**)
59 {
60   std::thread t1(f1);
61   std::thread t2(f2);
62   while (ready > 0)
63     std::this_thread::yield();
64   // In case the threads were preempted right after the atomic decrement but
65   // before cv.wait(), we yield one more time.
66   std::this_thread::yield();
67   {
68     std::unique_lock<std::mutex>lk(mut);
69     test1 = 1;
70     test2 = 1;
71     ready = 1;
72   }
73   cv.notify_one();
74   {
75     while (which == 0)
76       std::this_thread::yield();
77     std::unique_lock<std::mutex>lk(mut);
78   }
79   if (test1 == 2) {
80     assert(test2 == 1);
81     t1.join();
82     test1 = 0;
83   } else {
84     assert(test1 == 1);
85     assert(test2 == 2);
86     t2.join();
87     test2 = 0;
88   }
89   which = 0;
90   cv.notify_one();
91   {
92     while (which == 0)
93       std::this_thread::yield();
94     std::unique_lock<std::mutex>lk(mut);
95   }
96   if (test1 == 2) {
97     assert(test2 == 0);
98     t1.join();
99     test1 = 0;
100   } else {
101     assert(test1 == 0);
102     assert(test2 == 2);
103     t2.join();
104     test2 = 0;
105   }
106 
107   return 0;
108 }
109