socket not closed in a threaded server

[sylvain DELHOMME]

While playing with sockets and threads, I noticed that while my tcp socket is 
correctly closed, the associated udp socket (managed by Cygwin) is not. This 
was tested with(out) Firewall && Antivirus on 2 WinXP computers with cygwin 
1.5.25.

Is that a known problem with Cygwin (code is fine under Linux Debian) ?

testcase :

- ./main.exe (netstat shows 2 sockets (one tcp on port 1025 && one udp)
- telnet 127.0.0.1 1025 (netstat shows 4 sockets  : 2 tcp && 2 udp )
- netstat -ab shows 3 sockets (one tcp on port 1025 && two udp).

src :

--- begin ---

#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <pthread.h>
#include <unistd.h>
#include <netinet/in.h>
#include <errno.h>
#include <string.h>

#define MAXTHREADS 4

pthread_mutex_t __mutex = PTHREAD_MUTEX_INITIALIZER;

struct thrdata {
        int thrnum;
        pthread_t t;
        int socket_fd;
        int socket_errno;
}th[MAXTHREADS];

int thread_code( void *p );

int main(int argc, char **argv)
{
        int fd;
        struct sockaddr_in sa;
        int i;

        sa.sin_family = AF_INET;
        sa.sin_addr.s_addr = htonl(INADDR_ANY);
        sa.sin_port = htons(1025);

        fd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);

        printf("socket id : %d\n", fd);

        if( bind( fd, (struct sockaddr *)&sa, sizeof(sa) ) == -1 )
                printf("bind error\n");

        if( listen( fd, 0 ) == -1 )
                printf("listen error\n");

        printf("creating threads\n");

        for(i=0; i<MAXTHREADS; i++)
        {
                th[i].thrnum = i;
                th[i].socket_fd = fd;
                printf("thread %d\n", i);
                pthread_create(&th[i].t, NULL, thread_code, (void *)&(th[i]));
                sleep(1);
        }

        for(i=0; i<MAXTHREADS; i++) 
        {
                pthread_join(th[i].t, NULL);
        }

        printf("exiting\n");

        return 1;
}

int thread_code( void *p )
{
        struct thrdata *pt = (struct thrdata *)p;
        int fd = pt->socket_fd;
        int fd_client;
        struct sockaddr_in sa_client;
        int sin_size;
        int i;
        char buf;

        // printf("thread, fd : %d\n", fd);

        for( ;; )
        {
                pthread_mutex_lock(&__mutex); /* begin critical area */ 
                fd_client = accept( fd, (struct sockaddr *)&sa_client, 
&sin_size );
                
                if( fd_client < 0 )
                        printf("accept error\n");

                pthread_mutex_unlock(&__mutex); /* end critical area */

                if( fd_client > 0 )
                {
                        printf("accept fd : %d, fd_client : %d\n", fd, 
fd_client );
                        for(i=0; i<20; i++)
                        {
                                send( fd_client, "hello\n", strlen("hello"), 0 
);
                                sleep(1);
                        }
                        
                        printf("closing fd_client : %d\n", fd_client );
                        close( fd_client );
                }
        }

        return 1;
}

--- end ---

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