Server unexpectedly closed network connection - c

Question

I am running the following code using putty and the expected behaviour should be the following: when the thread responsible with the reading from a file has ended, the other thread responsible with the timer has to end too and reverse: if the thread responsible with the timer has ended, the other one has to end too. But i get this fatal error: Server unexpectedly closed network connection when there is one minute left. What i am doing wrong?
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
/* global variables to check the state*/
int read = 0;
int timeLeft = 0;
void *readFromFile(void *myFile)
{
int state;
char *theFile;
theFile = (char*) myFile;
char question[100];
char answer[100];
state = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL );
FILE *file = fopen(theFile, "r");
if (file != NULL )
{
while (fgets(question, sizeof question, file) != NULL )
{
fputs(question, stdout);
scanf("%s", &answer);
}
fclose(file);
state = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL );
printf("Done with questions!\n");
read = 1;
}
else
{
perror(theFile);
}
}
void displayTimeLeft(void *arg)
{
int *time;
int state;
time = (int*) arg;
int i;
state = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL );
for (i = time; i >= 0; i -= 60)
{
if (i / 60 != 0)
{
printf("You have %d %s left.\n", i / 60,
(i / 60 > 1) ? "minutes" : "minute");
sleep(60);
}
else
{
state = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL );
printf("The time is over \n");
timeLeft = 1;
break;
}
}
}
int main()
{
pthread_t thread1;
pthread_t thread2;
char *file = "/home/osystems01/laura/test";
int *time = 180;
int ret1;
int ret2;
ret1 = pthread_create(&thread1, NULL, readFromFile, file);
ret2 = pthread_create(&thread2, NULL, displayTimeLeft, time);
printf("Main function after pthread_create\n");
while (1)
{
if (read == 1)
{
pthread_cancel(thread2);
pthread_cancel(thread1);
break;
}
else if (timeLeft == 1)
{
pthread_cancel(thread1);
pthread_cancel(thread2);
break;
}
}
printf("After the while loop!\n");
return 0;
}

Answer 1

As mentioned in my comment I strongly doubt the server shuts down the connection established via putty because issues with your program.
However here are several issues with the program's code.
The ost critical issue is you are accessing the two global variable concurrently from two threads.
Concurrent access needs to be protected. To do so declare two mutexes like so:
pthread_mutex_t mutex_read = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex_time = PTHREAD_MUTEX_INITIALIZER;
void *readFromFile(void *myFile)
{
...
{
int result = pthread_mutex_lock(mutex_read);
if (0 != result)
{
perror("pthread_mutex_lock(mutex_read) failed");
}
}
read = 1;
{
int result = pthread_mutex_unlock(mutex_read);
if (0 != result)
{
perror("pthread_mutex_unlock(mutex_read) failed");
}
}
...
}
void displayTimeLeft(void *arg)
{
...
{
int result = pthread_mutex_lock(mutex_time);
if (0 != result)
{
perror("pthread_mutex_lock(mutex_time) failed");
}
}
timeLeft= 1;
{
int result = pthread_mutex_unlock(mutex_time);
if (0 != result)
{
perror("pthread_mutex_unlock(mutex_time) failed");
}
}
...
}
int main(void)
{
...
while(1)
{
int bread = 0;
int btimeLeft = 0;
{
int result = pthread_mutex_lock(mutex_read);
if (0 != result)
{
perror("pthread_mutex_lock() failed");
}
}
bread = (1 == read);
{
int result = pthread_mutex_unlock(mutex_read);
if (0 != result)
{
perror("pthread_mutex_unlock() failed");
}
}
{
int result = pthread_mutex_lock(mutex_time);
if (0 != result)
{
perror("pthread_mutex_lock() failed");
}
}
btimeLeft = (1 == timeLEft);
{
int result = pthread_mutex_unlock(mutex_time);
if (0 != result)
{
perror("pthread_mutex_unlock() failed");
}
}
if (bread == 1)
{
pthread_cancel(thread2);
pthread_cancel(thread1);
break;
}
else if (btimeLeft == 1)
{
pthread_cancel(thread1);
pthread_cancel(thread2);
break;
}
}
...
For PThreads thr threas function needs to be declared as:
void * (*) (void *)
This isn't the case for displayTimeLeft
When scanning in a "string" one need to pass the address of the first element of the character array representing the string. So this
scanf("%s", &answer);
should be this
scanf("%s", &answer[0]);
or this
scanf("%s", answer);
The code misses the protoype for sleep(), so add
#include <unistd.h>
Having done so the compiler detects a name clash between the system call read() and the global variable read declared by your code. This is not nice. Rename readto something like readit.
Last not least there is the issue mentioend by suspectus in his answer. You are misusing a pointer to an int to store some time value (int * time = 180). Do not do that.
To fix this do like so:
int main(void)
{
...
int time = 180;
...
ret2 = pthread_create(&thread2, NULL, displayTimeLeft, &time);
and in displayTimeLeft do:
int time = *((int*) arg);

Answer 2

Here you are initialising a pointer to the memory location 180.
int *time = 180;
What is needed is:
int time = 180;
...
...
ret2 = pthread_create(&thread2, NULL, displayTimeLeft, &time);