I'm writing a pthread server which takes requests from clients and sends them back a bunch of .ppm files. Everything seems to go well, but sometimes when I have just 1 client connected, when trying to read from the file descriptor (for the file), it says Bad file Descriptor. This doesn't make sense, since my int fd isn't -1, and the file most certainly exists. Other times, I get this "Socket operation on nonsocket" error. This is weird because other times, it doesn't give me this error and everything works fine.

When trying to connect multiple clients, for some reason, it will only send correctly to one, and then the other client gets the bad file descriptor or "nonsocket" error, even though both threads are processing the same messages and do the same routines. Anyone have an idea why? Here's the code that is giving me that error:

    while(mqueue.head != mqueue.tail && count < dis_m){
        printf("Sending to client %s: %s\n", pointer->id, pointer->message);
        int fd;
        fd = open(pointer->message,  O_RDONLY);

        char buf[58368];
        int bytesRead;
        printf("This is fd %d\n", fd);
        bytesRead=read(fd,buf,58368);

        send(pointer->socket,buf,bytesRead,0);


        perror("Error:\n");
        fflush(stdout);
        close(fd);

        mqueue.mcount--;
        mqueue.head = mqueue.head->next;
        free(pointer->message);
        free(pointer);
        pointer = mqueue.head;
        count++;

    }

    printf("Sending %s\n", pointer->message);
    int fd;
    fd = open(pointer->message,  O_RDONLY);
    printf("This is fd %d\n", fd);
    printf("I am hhere2\n");
    char buf[58368];
    int bytesRead;

    bytesRead=read(fd,buf,58368);

    send(pointer->socket,buf,bytesRead,0);


    perror("Error:\n");
    close(fd);
    mqueue.mcount--;

    if(mqueue.head != mqueue.tail){
        mqueue.head = mqueue.head->next;
    }
    else{

        mqueue.head->next = malloc(sizeof(struct message));
        mqueue.head = mqueue.head->next;
        mqueue.head->next = malloc(sizeof(struct message));
        mqueue.tail = mqueue.head->next;
        mqueue.head->message = NULL;
    }

    free(pointer->message);
    free(pointer);


    pthread_mutex_unlock(&numm);
    pthread_mutex_unlock(&circ);
    pthread_mutex_unlock(&slots);

The messages for both threads are the same, being of the form ./path/imageXX.ppm where XX is the number that should go to the client. The file size of each image is 58368 bytes.

Sometimes, this code hangs on the read, and stops execution. I don't know this would be either, because the file descriptor comes back as valid.

Thanks in advanced.

Edit:

Here's some sample output:

Sending to client a: ./support/images/sw90.ppm
This is fd 4
Error:
: Socket operation on non-socket
Sending to client a: ./support/images/sw91.ppm
This is fd 4
Error:
: Socket operation on non-socket
Sending ./support/images/sw92.ppm
This is fd 4
I am hhere2
Error:
: Socket operation on non-socket
My dispatcher has defeated evil

Sample with 2 clients (client b was serviced first) Sending to client b: ./support/images/sw87.ppm This is fd 6 Error: : Success Sending to client b: ./support/images/sw88.ppm This is fd 6 Error: : Success Sending to client b: ./support/images/sw89.ppm This is fd 6 Error: : Success

This is fd 6
Error:
: Bad file descriptor
Sending to client a: ./support/images/sw85.ppm
This is fd 6
Error:

As you can see, who ever is serviced first in this instance can open the files, but not the 2nd person.

Edit2:

Full code. Sorry, its pretty long and terribly formatted.

      #include <netinet/in.h>
        #include <netinet/in.h>
        #include <netdb.h>
        #include <arpa/inet.h>
        #include <sys/types.h>
        #include <sys/socket.h>
        #include <errno.h>
        #include <stdio.h>
        #include <unistd.h>
        #include <pthread.h>
        #include <stdlib.h>
        #include <string.h>
        #include <sys/types.h>
        #include <sys/stat.h>
        #include <fcntl.h>
        #include "ring.h"


        /*
        Version 1

        Here is what is implemented so far:

        The threads are created from the arguments specified (number of threads that is)
        The server will lock and update variables based on how many clients are in the system                    and such.

        The socket that is opened when a new client connects, must be passed to the threads.  To             do this, we need some sort of global array.  I did
        this by specifying an int client and main_pool_busy, and two pointers poolsockets and     nonpoolsockets.  

        My thinking on this was that when a new client enters the system, the server thread     increments the variable client.  When a thread is finished with this client (after it sends         it the data), the thread will decrement client and close the socket.  HTTP servers act this     way sometimes (they terminate the socket as soon as one transmission is sent). *Note down at     bottom  

    After the server portion increments the client counter, we must open up a new socket (denoted by new_sd) and get this value to the appropriate thread.
    To do this, I created global array poolsockets, which will hold all the socket descriptors for our pooled threads.  The server portion gets the new socket descriptor, and places the value in the first spot of the array that has a 0.  We only place a value in this array IF:

        1. The variable main_pool_busy < worknum (If we have more clients in the system than in our pool, it doesn't mean we should always create a new thread.

    At the end of this, the server signals on the condition variable clientin that a new client has arrived.  

    In our pooled thread, we then must walk this array and check the array until we hit our first non-zero value. This is the socket we will give to that thread.  The thread then changes the array to have a zero here.  

    What if our all threads in our pool our busy?

    If this is the case, then we will know it because our threads in this pool will increment main_pool_busy by one when they are working on a request and decrement it when they are done.  If main_pool_busy >= worknum, then we must dynamically create a new thread.  Then, we must realloc the size of our 
    nonpoolsockets array by 1 int.  We then add the new socket descriptor to our pool.  

    Here's what we need to figure out:

    NOTE* Each worker should generate 100 messages which specify the worker thread ID, client socket descriptor and a copy of the client message. Additionally, each message should include a message number, starting from 0 and incrementing for each subsequent message sent to the same client.

    I don't know how to keep track of how many messages were to the same client.  Maybe we shouldn't close the socket descriptor, but rather keep an array of structs for each socket that includes how many messages they have been sent.  Then, the server adds the struct, the threads remove it, then the threads add it back once they've serviced one request (unless the count is 100).  


    -------------------------------------------------------------
    CHANGES

    Version 1

----------
NONE: this is the first version.  
*/


#define MAXSLOTS 30
#define dis_m 15 //problems with dis_m ==1





//Function prototypes
void inc_clients();
void init_mutex_stuff(pthread_t*, pthread_t*);
void *threadpool(void *);
void server(int);
void add_to_socket_pool(int);
void inc_busy();
void dec_busy();
void *dispatcher();
void create_message(long, int, int, char *, char *);
void init_ring();
void add_to_ring(char *, char *, int, int, int);
int socket_from_string(char *);
void add_to_head(char *);
void add_to_tail(char *);
struct message * reorder(struct message *, struct message *, int);
int get_threadid(char *);
void delete_socket_messages(int);
struct message * merge(struct message *, struct message *, int);
int get_request(char *, char *, char*);
/////////////////////


//Global mutexes and condition variables
pthread_mutex_t startservice;
pthread_mutex_t numclients;
pthread_mutex_t pool_sockets;
pthread_mutex_t nonpool_sockets;
pthread_mutex_t m_pool_busy;
pthread_mutex_t slots;
pthread_mutex_t numm;
pthread_mutex_t circ;

pthread_cond_t clientin;
pthread_cond_t m;
///////////////////////////////////////


//Global variables
int clients;
int main_pool_busy;
int * poolsockets, nonpoolsockets;
int worknum;
struct ring mqueue;
///////////////////////////////////////


int main(int argc, char ** argv){

    //error handling if not enough arguments to program 
    if(argc != 3){
        printf("Not enough arguments to server: ./server portnum NumThreadsinPool\n");
        _exit(-1);
    }
    //Convert arguments from strings to integer values

    int port = atoi(argv[1]);
    worknum = atoi(argv[2]);

    //Start server portion  
    server(port);

}
///////////////////////////////////////////////////////////////////////////////////////////////
//The listen server thread/////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////////
void server(int port){

  int sd, new_sd;
  struct sockaddr_in name, cli_name;
  int sock_opt_val = 1;
  int cli_len;

  pthread_t threads[worknum]; //create our pthread id array
  pthread_t dis[1]; //create our dispatcher array (necessary to create thread)

  init_mutex_stuff(threads, dis); //initialize mutexes and stuff

//Server setup /////////////////////////////////////////////////////// 
  if ((sd = socket (AF_INET, SOCK_STREAM, 0)) < 0) {
    perror("(servConn): socket() error");
    _exit (-1);
  }

  if (setsockopt (sd, SOL_SOCKET, SO_REUSEADDR, (char *) &sock_opt_val,
          sizeof(sock_opt_val)) < 0) {
    perror ("(servConn): Failed to set SO_REUSEADDR on INET socket");
    _exit (-1);
  }

  name.sin_family = AF_INET;
  name.sin_port = htons (port);
  name.sin_addr.s_addr = htonl(INADDR_ANY);

  if (bind (sd, (struct sockaddr *)&name, sizeof(name)) < 0) {
    perror ("(servConn): bind() error");
    _exit (-1);
  }

  listen (sd, 5);
//End of server Setup //////////////////////////////////////////////////

  for (;;) {

      cli_len = sizeof (cli_name);
      new_sd = accept (sd, (struct sockaddr *) &cli_name, &cli_len);
      printf ("Assigning new socket descriptor:  %d\n", new_sd);
      inc_clients(); //New client has come in, increment clients
      add_to_socket_pool(new_sd); //Add client to the pool of sockets

      if (new_sd < 0) {
    perror ("(servConn): accept() error");
    _exit (-1);
      }


  }

    pthread_exit(NULL); //Quit
}

//Adds the new socket to the array designated for pthreads in the pool
void add_to_socket_pool(int socket){

    pthread_mutex_lock(&m_pool_busy); //Lock so that we can check main_pool_busy
    int i;

    //If not all our main pool is busy, then allocate to one of them
    if(main_pool_busy < worknum){
        pthread_mutex_unlock(&m_pool_busy); //unlock busy, we no longer need to hold it
        pthread_mutex_lock(&pool_sockets); //Lock the socket pool array so that we can edit it without worry
        for(i = 0; i < worknum; i++){ //Find a poolsocket that is -1; then we should put the real socket there.  This value will be changed back to -1 when the thread grabs the sockfd
            if(poolsockets[i] == -1){
                poolsockets[i] = socket;
                pthread_mutex_unlock(&pool_sockets); //unlock our pool array, we don't need it anymore
                inc_busy(); //Incrememnt busy (locks the mutex itself)
                pthread_cond_signal(&clientin); //Signal first thread waiting on a client that a client needs to be serviced
                break;
            } 
        }


    }
    else{  //Dynamic thread creation goes here
    pthread_mutex_unlock(&m_pool_busy);
    }
}

//Increments the client number.  If client number goes over worknum, we must dynamically create new pthreads
void inc_clients(){

      pthread_mutex_lock(&numclients);
      clients++;
      pthread_mutex_unlock(&numclients);

}
//Increments busy
void inc_busy(){

    pthread_mutex_lock(&m_pool_busy);
    main_pool_busy++;
    pthread_mutex_unlock(&m_pool_busy); 

}



//Initialize all of our mutexes at the beginning and create our pthreads
  void init_mutex_stuff(pthread_t * threads, pthread_t * dis){

  pthread_mutex_init(&startservice, NULL);
  pthread_mutex_init(&numclients, NULL);
  pthread_mutex_init(&pool_sockets, NULL);
  pthread_mutex_init(&nonpool_sockets, NULL);
  pthread_mutex_init(&m_pool_busy, NULL);
  pthread_mutex_init(&circ, NULL);

   pthread_cond_init (&clientin, NULL);

   main_pool_busy = 0;

   poolsockets = malloc(sizeof(int)*worknum);

   int threadreturn;  //error checking variables

   long i = 0; //Loop and create pthreads 

   for(i; i < worknum; i++){
    threadreturn = pthread_create(&threads[i], NULL, threadpool, (void *) i);
        poolsockets[i] = -1; 
    if(threadreturn){
        perror("Thread pool created unsuccessfully");
        _exit(-1);
    }
  }
    pthread_create(&dis[0], NULL, dispatcher, NULL);





}


//////////////////////////////////////////////////////////////////////////////////////////
/////////Main pool routines
/////////////////////////////////////////////////////////////////////////////////////////

void dec_busy(){

    pthread_mutex_lock(&m_pool_busy);
    main_pool_busy--;
    pthread_mutex_unlock(&m_pool_busy); 

}

void dec_clients(){
      pthread_mutex_lock(&numclients);
      clients--;
      pthread_mutex_unlock(&numclients);

}


//This is what our threadpool pthreads will be running.
void *threadpool(void * threadid){

    long id = (long) threadid; //Id of this thread
    int i;
    int socket;
    int counter = 0;

    //Try and gain access to the next client that comes in and wait until server signals that a client as arrived

    while(1){   
        pthread_mutex_lock(&startservice); //lock start service (required for cond wait)
        pthread_cond_wait(&clientin, &startservice); //wait for signal from server that client exists
        pthread_mutex_unlock(&startservice); //unlock mutex.

        pthread_mutex_lock(&pool_sockets); //Lock the pool socket so we can get the socket fd unhindered/interrupted

    for(i = 0; i < worknum; i++){
        if(poolsockets[i] != -1){
            socket = poolsockets[i];
            poolsockets[i] = -1;
            pthread_mutex_unlock(&pool_sockets);
        }
    }
    printf("Thread #%d is past getting the socket\n", id);


    int incoming = 1;

    while(counter < 100 && incoming != 0){


        char buffer[512];
        bzero(buffer,512);
        int startcounter = 0;

        incoming = read(socket, buffer, 512);

        if(buffer[0] != 0){
            //client ID:priority:request:arguments
            char id[100];
            long prior;
            char request[100];
            char arg1[100];
            char message[100];
            char arg2[100];
            char * point;
            point = strtok(buffer, ":");
            strcpy(id, point);
            point = strtok(NULL, ":");
            prior = atoi(point);
            point = strtok(NULL, ":");
            strcpy(request, point);
            point = strtok(NULL, ":");
            strcpy(arg1, point);
            point = strtok(NULL, ":");
            if(point != NULL){
                strcpy(arg2, point);
            }

            int fd;
            if(strcmp(request, "start_movie") == 0){
                int count = 1;
                while(count <= 100){

                char temp[10];
                snprintf(temp, 50, "%d\0", count);

                strcpy(message, "./support/images/");

                strcat(message, arg1);

                strcat(message, temp);
                strcat(message, ".ppm");
                printf("This is message %s to %s\n", message, id);
                count++;
                add_to_ring(message, id, prior, counter, socket); //Adds our created message to the ring

                counter++;
                }
                printf("I'm out of the loop\n");
            }
            else if(strcmp(request, "seek_movie") == 0){
                int count = atoi(arg2);
                while(count <= 100){

                char temp[10];
                snprintf(temp, 10, "%d\0", count);

                strcpy(message, "./support/images/");

                strcat(message, arg1);

                strcat(message, temp);
                strcat(message, ".ppm");
                printf("This is message %s\n", message);
                count++;
                }

            }


            //create_message(id, socket, counter, buffer, message); //Creates our message from the input from the client. Stores it in buffer


        }
        else{
            delete_socket_messages(socket);
            break;
        }
    }   

        counter = 0; 
        close(socket);//Zero out counter again
    }
    dec_clients(); //client serviced, decrement clients
    dec_busy(); //thread finished, decrement busy
}

//Creates a message



void create_message(long threadid, int socket, int counter, char * buffer, char * message){

    snprintf(message, strlen(buffer)+15, "%d:%d:%d:%s", threadid, socket, counter, buffer);

}
//Gets the socket from the message string (maybe I should just pass in the socket to another method)
int socket_from_string(char * message){
    char * substr1 = strstr(message, ":");
    char * substr2 = substr1;
    substr2++;
    int occurance = strcspn(substr2, ":");
    char sock[10]; 
    strncpy(sock, substr2, occurance);
    return atoi(sock);

}
//Adds message to our ring buffer's head
void add_to_head(char * message){
    printf("Adding to head of ring\n");
    mqueue.head->message = malloc(strlen(message)+1); //Allocate space for message
    strcpy(mqueue.head->message, message); //copy bytes into allocated space


}
//Adds our message to our ring buffer's tail
void add_to_tail(char * message){
    printf("Adding to tail of ring\n");
    mqueue.tail->message = malloc(strlen(message)+1); //allocate space for message
    strcpy(mqueue.tail->message, message); //copy bytes into allocated space
    mqueue.tail->next = malloc(sizeof(struct message)); //allocate space for the next message struct
}
//Adds a message to our ring
void add_to_ring(char * message, char * id, int prior, int mnum, int socket){
    //printf("This is message %s:" , message);

    pthread_mutex_lock(&circ); //Lock the ring buffer   
    pthread_mutex_lock(&numm); //Lock the message count (will need this to make sure we can't fill the buffer over the max slots)



    if(mqueue.head->message == NULL){
        add_to_head(message); //Adds it to head
        mqueue.head->socket = socket; //Set message socket
        mqueue.head->priority = prior; //Set its priority (thread id)
        mqueue.head->mnum = mnum; //Set its message number (used for sorting)
        mqueue.head->id = malloc(sizeof(id));
        strcpy(mqueue.head->id, id);
    }
    else if(mqueue.tail->message == NULL){ //This is the problem for dis_m 1 I'm pretty sure
        add_to_tail(message);
        mqueue.tail->socket = socket;
        mqueue.tail->priority = prior;
        mqueue.tail->mnum = mnum;
        mqueue.tail->id = malloc(sizeof(id));
        strcpy(mqueue.tail->id, id);
    }
    else{
        mqueue.tail->next = malloc(sizeof(struct message));
        mqueue.tail = mqueue.tail->next;
        add_to_tail(message);
        mqueue.tail->socket = socket;
        mqueue.tail->priority = prior;
        mqueue.tail->mnum = mnum;
        mqueue.tail->id = malloc(sizeof(id));
        strcpy(mqueue.tail->id, id);

    }

    mqueue.mcount++;
    pthread_mutex_unlock(&circ);

    if(mqueue.mcount >= dis_m){
        pthread_mutex_unlock(&numm);
        pthread_cond_signal(&m);
    }
    else{
        pthread_mutex_unlock(&numm);
    }

    printf("out of add to ring\n");
    fflush(stdout);
}


//////////////////////////////////
//Dispatcher routines
/////////////////////////////////

void *dispatcher(){

    init_ring();

    while(1){
        pthread_mutex_lock(&slots);
        pthread_cond_wait(&m, &slots);


        pthread_mutex_lock(&numm);
        pthread_mutex_lock(&circ);

        printf("Dispatcher to the rescue!\n");

        mqueue.head = reorder(mqueue.head, mqueue.tail, mqueue.mcount);
        //printf("This is the head %s\n", mqueue.head->message);
        //printf("This is the tail %s\n", mqueue.head->message);
        fflush(stdout);
        struct message * pointer = mqueue.head;
        int count = 0;

        while(mqueue.head != mqueue.tail && count < dis_m){
            printf("Sending to client %s: %s\n", pointer->id, pointer->message);
            int fd;
            fd = open(pointer->message,  O_RDONLY);

            char buf[58368];
            int bytesRead;
            printf("This is fd %d\n", fd);
            bytesRead=read(fd,buf,58368);

            send(pointer->socket,buf,bytesRead,0);


            perror("Error:\n");
            fflush(stdout);
            close(fd);

            mqueue.mcount--;
            mqueue.head = mqueue.head->next;
            free(pointer->message);
            free(pointer);
            pointer = mqueue.head;
            count++;

        }

        printf("Sending %s\n", pointer->message);
        int fd;
        fd = open(pointer->message,  O_RDONLY);
        printf("This is fd %d\n", fd);
        printf("I am hhere2\n");
        char buf[58368];
        int bytesRead;

        bytesRead=read(fd,buf,58368);

        send(pointer->socket,buf,bytesRead,0);


        perror("Error:\n");
        close(fd);
        mqueue.mcount--;

        if(mqueue.head != mqueue.tail){
            mqueue.head = mqueue.head->next;
        }
        else{

            mqueue.head->next = malloc(sizeof(struct message));
            mqueue.head = mqueue.head->next;
            mqueue.head->next = malloc(sizeof(struct message));
            mqueue.tail = mqueue.head->next;
            mqueue.head->message = NULL;
        }

        free(pointer->message);
        free(pointer);


        pthread_mutex_unlock(&numm);
        pthread_mutex_unlock(&circ);
        pthread_mutex_unlock(&slots);
        printf("My dispatcher has defeated evil\n");

    }

}

void init_ring(){

    mqueue.head = malloc(sizeof(struct message));
    mqueue.head->next = malloc(sizeof(struct message));
    mqueue.tail = mqueue.head->next;
    mqueue.mcount = 0;
}

struct message * reorder(struct message * begin, struct message * end, int num){
    //printf("I am reordering for size %d\n", num);
    fflush(stdout);
    int i;
    if(num == 1){
        //printf("Begin: %s\n", begin->message);
        begin->next = NULL;
        return begin;
    }
    else{
        struct message * left = begin;
        struct message * right;
        int middle = num/2;

        for(i = 1; i < middle; i++){
            left = left->next;
        }
        right = left -> next;
        left -> next = NULL;

        //printf("Begin: %s\nLeft: %s\nright: %s\nend:%s\n", begin->message, left->message, right->message, end->message);
        left = reorder(begin, left, middle);
        if(num%2 != 0){
        right = reorder(right, end, middle+1);
        }
        else{
            right = reorder(right, end, middle);
        }
        return merge(left, right, num);

    }

}

struct message * merge(struct message * left, struct message * right, int num){
    //printf("I am merginging! left: %s %d, right: %s %dnum: %d\n", left->message,left->priority, right->message, right->priority, num);
    struct message * start, * point;
    int lenL= 0;
    int lenR = 0;
    int flagL = 0;
    int flagR = 0;
    int count = 0;
    int middle1 = num/2;
    int middle2;
    if(num%2 != 0){
        middle2 = middle1+1;
    }
    else{
        middle2 = middle1;
    }

    while(lenL < middle1 && lenR < middle2){
        count++;
        //printf("In here for count %d\n", count);

        if(lenL == 0 && lenR == 0){

            if(left->priority < right->priority){

                start = left; //Set the start point
                point = left; //set our enum;

                left = left->next; //move the left pointer
                point->next = NULL; //Set the next node to NULL
                lenL++;
            }
            else if(left->priority > right->priority){
                start = right;
                point = right;
                right = right->next;
                point->next = NULL;
                lenR++;
            }
            else{
                if(left->mnum < right->mnum){
                    ////printf("This is where we are\n");
                    start = left; //Set the start point
                    point = left; //set our enum;
                    left = left->next; //move the left pointer
                    point->next = NULL; //Set the next node to NULL
                    lenL++;

                }
                else{
                    start = right;
                    point = right;
                    right = right->next;
                    point->next = NULL;
                    lenR++;
                }

            }

        }
        else{
            if(left->priority < right->priority){

                point->next = left;
                left = left->next; //move the left pointer
                point = point->next;
                point->next = NULL; //Set the next node to NULL
                lenL++;
            }
            else if(left->priority > right->priority){
                point->next = right;
                right = right->next;
                point = point->next;
                point->next = NULL;
                lenR++;
            }
            else{
                if(left->mnum < right->mnum){
                    point->next = left; //set our enum;
                    left = left->next;
                    point = point->next;//move the left pointer
                    point->next = NULL; //Set the next node to NULL
                    lenL++;

                }
                else{
                    point->next = right;
                    right = right->next;
                    point = point->next;
                    point->next = NULL;
                    lenR++;
                }

            }

        }

        if(lenL == middle1){
            flagL = 1;
            break;
        }
        if(lenR == middle2){
            flagR = 1;
            break;
        }


    }

    if(flagL == 1){
        point->next = right;
        point = point->next;
        for(lenR; lenR< middle2-1; lenR++){
            point = point->next;
        }
        point->next = NULL;
        mqueue.tail = point;
    }
    else{
        point->next = left;
        point = point->next;
            for(lenL; lenL< middle1-1; lenL++){
                point = point->next;
            }
            point->next = NULL;
            mqueue.tail = point;
        }
        //printf("This is the start %s\n", start->message);
        //printf("This is mqueue.tail %s\n", mqueue.tail->message);
        return start;

    }   





    void delete_socket_messages(int a){

    }