Dubious behaviour in multithreaded client-server in C - multithreading

Question

void* thread_request_server_static(void* args); , This is where the worker threads will handle the connection (i have got 4 threads created)
request.c:
struct conn_args
{
int fd;
int filename;
int filesize;
struct conn_args *next;
}
/* other functions */
int add(int fd, char *filename, int filesize)
{
if(buffer_size >= buffer_max_size)
return 1;
struct conn_args *temp = malloc(sizeof(struct conn_args));
temp->fd = fd;
temp->filename = filename;
temp->filesize = filesize;
temp->next = NULL;
if (head == NULL)
{
head = temp;
tail = temp;
}
else
{
tail->next = temp;
tail = temp;
}
buffer_size++;
return 0;
}
struct conn_args* get_args()
{
struct conn_args *temp = NULL;
if(head!=NULL)
{
temp = head;
head = head->next;
buffer_size--;
}
return temp;
}
void *thread_request_serve_static(void *arg)
{
while (1)
{
pthread_mutex_lock(&lock);
struct conn_args *arg = get_args();
if (!arg)
pthread_cond_wait(&c, &lock);
else
{
request_serve_static(arg->fd, arg->filename, arg->filesize);
printf("Request for %s is removed from the buffer\n-----------------\n",
arg->filename);
close_or_die(arg->fd);
free(arg);
}
pthread_mutex_unlock(&lock);
}
// TODO: write code to actualy respond to HTTP requests
}
void request_handle(int fd)
{
/* variable declarations and condition checks */
pthread_mutex_lock(&lock);
int stat = add(fd, filename, sbuf.st_size);
pthread_mutex_unlock(&lock);
if (!stat)
{
printf("-----------------\nRequest for %s is added to the buffer\n",
filename);
pthread_cond_signal(&c); // wake up thread since connections arrive at the buffer.
}
else
{
printf("Server overload: Try again later!");
}
}
wserver.c:
int main(int argc, char *argv[])
{
/* variable initializations and argument reading */
pthread_t thread_pool[num_threads];
for(int i=0; i<num_threads; i++)
pthread_create(&thread_pool[i], NULL, thread_request_serve_static, NULL);
// open the socket connection
int listen_fd = open_listen_fd_or_die(port);
while (1) {
// start accepting HTTP requests from client
struct sockaddr_in client_addr;
int client_len = sizeof(client_addr);
int conn_fd = accept_or_die(listen_fd, (sockaddr_t *) &client_addr, (socklen_t *) &client_len);
// process the HTTP request
request_handle(conn_fd);
// close the connection to client
//close_or_die(conn_fd); // this has to be carefully done at the correct time in request.c
}
Starting the server,
./wserver -p 8003 (port 8003)
bash file for testing multiple connections,
multiple_clients.bash:
echo Starting requests
for ((i=15;i>0;i-=1))
do
./wclient localhost 8003 /files/test$i.html &
done
echo Requests completed
I piped the output into a test.txt and got the following, bash multiple_clients.bash > test.txt
test.txt:
/* Meta data */
This is a test HTML file -------------- 15.
/* Meta data */
/* Meta data */
This is a test HTML file ------------ 13.
/* Meta data */
/* Meta data */
This is a test HTML file ------------ 13.
/* Meta data */
/* Meta data */
This is a test HTML file ---------- 11.
/* Meta data */
/* Meta data */
This is a test HTML file --------- 10.
/* Meta data */
/* Meta data */
This is a test HTML file ---------- 11.
/* Meta data */
/* Meta data */
This is a test HTML file ----- 6.
/* Meta data */
/* Meta data */
This is a test HTML file 1.
/* Meta data */
/* Meta data */
This is a test HTML file - 2.
/* Meta data */
/* Meta data */
This is a test HTML file --- 4.
/* Meta data */
/* Meta data */
This is a test HTML file - 2.
/* Meta data */
/* Meta data */
This is a test HTML file -------- 9.
/* Meta data */
/* Meta data */
This is a test HTML file -- 3.
/* Meta data */
/* Meta data */
This is a test HTML file ---- 5.
/* Meta data */
/* Meta data */
This is a test HTML file ------- 8.
/* Meta data */
As you can see, some files are getting repeated and some are not showing up (7 and 14). Why is this? Although the total output file count is 15, this probably means it is successfully adding all the files to the buffer, but somehow skipping some files and producing duplicates of others.
The program doesn't even crash on double free error, so how is a single file getting handled twice?
Do let me know if any more info is required.
Any help would be appreciated.