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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
     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
     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 *
     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 
     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