I am trying to add some threads to my distributed FTP code. I'm using the pthreads library. When I compile my code through gcc, here is the error I get:

..
gcc: -lpthread: linker input file unused because linking not done
gcc -O2 -g -lpthread -Wall -W -Wpointer-arith -Wbad-function-cast -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wnested-externs -Winline -D__USE_READLINE__ ruserpass.c -c
gcc: -lpthread: linker input file unused because linking not done
gcc cmds.o cmdtab.o domacro.o ftp.o glob.o main.o ruserpass.o -lreadline -lncurses -o ftp
cmds.o(.text+0x1171): In function `init':
/home/hussain/netkit-ftp-0.17/ftp/cmds.c:827: undefined reference to `pthread_create'
collect2: ld returned 1 exit status
make: *** [ftp] Error 1

Any guidance on why I'm getting this error would be highly appreciated.


UPDATE : I fixed it, basically the issue was I was putting the "-lpthread" in the makefile at the wrong place. It should be before you make an executable!

Only use -l when linking the final executable, not when building the .o files.

Edit: Oops, didn't see the update.

Thanks for the response. I'm having another problem which is that I after I pass in a port to be used as a socket, I am unable to bind() on it again for sometime. Now I thought that by using close or shutdown on the sockfd, I would be able to use that port again. This doesn' seem to be true. Any clues on how to reuse the same port after I've done some data send/receive on it?

Try reading
http://beej.us/guide/bgnet/

First, sockets have a tendency to stick around after they are supposed to be dead. For reusing the same port, accept() returns a brand new file descripter for communicating with a specific client.

Thanks for that link. It's quite useful. However, I tried this:

int yes=1;
if (setsockopt(listener,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}

But after I bind, I still get the "Address already in use" error msg. Now I'm thinking that might have something to do with how I've written my code. I have a main program thread that creates (pthread_create) n threads to listen on n ports. This is not a thread pool so I want the threads to die after completing their job of listening and writing their contents onto file. Now in order make the threads exit, I tried using pthread_join right after I create them. But that doesn't seem to work. Any ideas as to where I should use pthread_join call? Could the threads being still alive after listening and outputting to file be the reason why the my program is unable to bind on the same port(s)?