1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
| //===-- main.cpp ------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include <chrono>
#include <condition_variable>
#include <cstdio>
#include <random>
#include <thread>
std::default_random_engine g_random_engine{std::random_device{}()};
std::uniform_int_distribution<> g_distribution{0, 3000000};
std::condition_variable g_condition_variable;
std::mutex g_mutex;
int g_count;
char *g_char_ptr = nullptr;
void
barrier_wait()
{
std::unique_lock<std::mutex> lock{g_mutex};
if (--g_count > 0)
g_condition_variable.wait(lock);
else
g_condition_variable.notify_all();
}
void
do_bad_thing_with_location(char *char_ptr, char new_val)
{
unsigned what = new_val;
printf("new value written to location(%p) = %u\n", char_ptr, what);
*char_ptr = new_val;
}
uint32_t
access_pool (bool flag = false)
{
static std::mutex g_access_mutex;
g_access_mutex.lock();
char old_val = *g_char_ptr;
if (flag)
do_bad_thing_with_location(g_char_ptr, old_val + 1);
g_access_mutex.unlock();
return *g_char_ptr;
}
void
thread_func (uint32_t thread_index)
{
printf ("%s (thread index = %u) startng...\n", __FUNCTION__, thread_index);
barrier_wait();
uint32_t count = 0;
uint32_t val;
while (count++ < 15)
{
// random micro second sleep from zero to 3 seconds
int usec = g_distribution(g_random_engine);
printf ("%s (thread = %u) doing a usleep (%d)...\n", __FUNCTION__, thread_index, usec);
std::this_thread::sleep_for(std::chrono::microseconds{usec});
if (count < 7)
val = access_pool ();
else
val = access_pool (true);
printf ("%s (thread = %u) after usleep access_pool returns %d (count=%d)...\n", __FUNCTION__, thread_index, val, count);
}
printf ("%s (thread index = %u) exiting...\n", __FUNCTION__, thread_index);
}
int main (int argc, char const *argv[])
{
g_count = 4;
std::thread threads[3];
g_char_ptr = new char{};
// Create 3 threads
for (auto &thread : threads)
thread = std::thread{thread_func, std::distance(threads, &thread)};
printf ("Before turning all three threads loose...\n"); // Set break point at this line.
barrier_wait();
// Join all of our threads
for (auto &thread : threads)
thread.join();
delete g_char_ptr;
return 0;
}
|