accept returns existing connection, causing seg fault - c

Question

I am creating a server daemon in c that accepts numerous simultaneous connections, and the clients will be sending data to the server. I currently have each client connection being spawned into a new thread. I am seeing that accept() will sometimes (not always) return the ID of existing connection which (obviously) causes a wide variety of issues, including segmentation faults.
I even turned off the socket option SO_REUSEADDR to make sure that wasn't the case. Whenever a single client makes numerous consecutive calls, everything is fine (conid in my code below increments - 5,6,7,8,9, etc...). But whenever more than one client ties to simultaneously connect, sometimes conid gets duplicated (an example from one run: 5,6,7,7,8,9,10,10,10,11,12,12, ...).
I'm wondering how accept() can return an existing connection?? It would make sense if I was calling accept() within more than one thread, but as you can see below it only exists in the main process thread. On the other hand, I never experienced this issue with select(), so maybe it is an issue with threading??? At this point, I've tried just about everything I can think of, but it's apparent to me I'm just missing something
Edit: edited code to show that mystruct wasn't being free'd in the while loop, and (hopefully) provide more insight.
Edit #2: per request, I have posted the full source of my example.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <stdarg.h>
#include <time.h>
#include <errno.h>
#include <netdb.h>
//this is my test structure
struct mystruct_ {
int id; //only id for testing
};
typedef struct mystruct_ mystruct;
//error logging function
void merr(const char *msg, ...) {
//get the time
time_t t;
time(&t);
//grab this function's arguments
va_list args;
char buf[BUFSIZ];
va_start(args,msg);
//build the message
vsprintf(buf,msg,args);
//output the message
printf(" ERROR :: %s\n",buf);
//that's it!
va_end(args);
}
//this function handles the threads
void *ThreadedFunction(void *arg) {
//get the passed structure
mystruct *test = (mystruct *)arg;
//print conid -- this is where I am seeing the duplicates
printf("my connection id is %d\n",test->id);
// do some stuff, like: pull vars out of mystruct
int nbytes;
char buf[256];
while(1) {
if((nbytes=recv(test->id, buf, sizeof buf, 0)) <= 0) {
//handle break in connection
close(test->id);
} else {
//for this example, just print out data from client to make my point
buf[nbytes] = 0;
printf("%s",buf);
}
}
}
//main just sets up the connections and creates threads
int main(int argc, char *argv[])
{
char *port = "1234";
//get ready for connection
struct sockaddr_storage addr;
socklen_t addrsize = sizeof addr;
struct addrinfo hints, *res, *ai, *p;
int sockfd, conid, rv;
int yes = 1;
//
//load up address structs with getaddrinfo():
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // use IPv4 or IPv6, whichever
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // fill in my IP for me
if((rv = getaddrinfo(NULL, port, &hints, &ai))!= 0) {
merr("failed to bind port '%s': %s\n",port,gai_strerror(rv));
exit(1);
}
//
//bind the port
for(p=ai; p!=NULL; p=p->ai_next) {
sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if(sockfd<0) continue;
//setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)); //commented for testing
if(bind(sockfd,p->ai_addr,p->ai_addrlen)<0) { close(sockfd); continue; }
break;
}
//if we don't have p, it means server didn't get bound
if(p==NULL) { merr("failed to bind port '%s' (reason unknown)",port); exit(2); }
freeaddrinfo(ai); //all done with this
//
// listen to the (now bounded) socket:
if(listen(sockfd,10)==-1) { merr("listen; errmsg: \"%s\"",strerror(errno)); exit(3); }
// bind(), listen(), etc... blah blah blah
mystruct test[1024]; //just for testing
printf("Ready and Listening...\n");
while(1) {
conid = accept(sockfd, (struct sockaddr *)&addr, &addrsize);//get a connection
test[conid].id = conid;
pthread_t p;
pthread_create(&p,NULL,ThreadedFunction,&test[conid]); //create new thread
}
}

Answer 1

This is broken:
while(1) {
conid = accept(sockfd, (struct sockaddr *)&addr, &addrsize);//get a connection
test[conid].id = conid;
pthread_t p;
pthread_create(&p,NULL,ThreadedFunction,&test[conid]); //create new thread
}
pthread_t p; declares an opaque handle on the stack which pthread_create will fill in. That handle's lifetime must last until you call pthread_join or pthread_detach.
In this case, the storage for that pthread_t is probably being reused, messing up the passing of the argument to the thread function. At least, that is my guess.
Try calling pthread_detach after pthread_create.

Answer 2

accept returns a file descriptor that my be reused. As your ThreadedFunction never terminates when done with a file descriptor you will get a race condition. So after the close statement put return;