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1 //===-- main.cpp ------------------------------------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 // C includes
11 #include <pthread.h>
12 #include <stdio.h>
13 #include <stdint.h>
14 #include <stdlib.h>
15 #include <unistd.h>
16 
17 pthread_t g_thread_1 = NULL;
18 pthread_t g_thread_2 = NULL;
19 pthread_t g_thread_3 = NULL;
20 
21 char *g_char_ptr = NULL;
22 
23 void
do_bad_thing_with_location(char * char_ptr,char new_val)24 do_bad_thing_with_location(char *char_ptr, char new_val)
25 {
26     unsigned what = new_val;
27     printf("new value written to location(%p) = %u\n", char_ptr, what);
28     *char_ptr = new_val;
29 }
30 
31 uint32_t access_pool (uint32_t flag = 0);
32 
33 uint32_t
access_pool(uint32_t flag)34 access_pool (uint32_t flag)
35 {
36     static pthread_mutex_t g_access_mutex = PTHREAD_MUTEX_INITIALIZER;
37     if (flag == 0)
38         ::pthread_mutex_lock (&g_access_mutex);
39 
40     char old_val = *g_char_ptr;
41     if (flag != 0)
42         do_bad_thing_with_location(g_char_ptr, old_val + 1);
43 
44     if (flag == 0)
45         ::pthread_mutex_unlock (&g_access_mutex);
46     return *g_char_ptr;
47 }
48 
49 void *
thread_func(void * arg)50 thread_func (void *arg)
51 {
52     uint32_t thread_index = *((uint32_t *)arg);
53     printf ("%s (thread index = %u) startng...\n", __FUNCTION__, thread_index);
54 
55     uint32_t count = 0;
56     uint32_t val;
57     while (count++ < 15)
58     {
59         // random micro second sleep from zero to 3 seconds
60         int usec = ::rand() % 3000000;
61         printf ("%s (thread = %u) doing a usleep (%d)...\n", __FUNCTION__, thread_index, usec);
62         ::usleep (usec);
63 
64         if (count < 7)
65             val = access_pool ();
66         else
67             val = access_pool (1);
68 
69         printf ("%s (thread = %u) after usleep access_pool returns %d (count=%d)...\n", __FUNCTION__, thread_index, val, count);
70     }
71     printf ("%s (thread index = %u) exiting...\n", __FUNCTION__, thread_index);
72     return NULL;
73 }
74 
75 
main(int argc,char const * argv[])76 int main (int argc, char const *argv[])
77 {
78     int err;
79     void *thread_result = NULL;
80     uint32_t thread_index_1 = 1;
81     uint32_t thread_index_2 = 2;
82     uint32_t thread_index_3 = 3;
83 
84     g_char_ptr = (char *)malloc (1);
85     *g_char_ptr = 0;
86 
87     // Create 3 threads
88     err = ::pthread_create (&g_thread_1, NULL, thread_func, &thread_index_1);
89     err = ::pthread_create (&g_thread_2, NULL, thread_func, &thread_index_2);
90     err = ::pthread_create (&g_thread_3, NULL, thread_func, &thread_index_3);
91 
92     printf ("Before turning all three threads loose...\n"); // Set break point at this line.
93 
94     // Join all of our threads
95     err = ::pthread_join (g_thread_1, &thread_result);
96     err = ::pthread_join (g_thread_2, &thread_result);
97     err = ::pthread_join (g_thread_3, &thread_result);
98 
99     return 0;
100 }
101