The problem *********** What I want to fix is this > netstat -an TCP 65.96.132.163:22 65.114.186.130:4762 CLOSE_WAIT TCP 65.96.132.163:22 65.114.186.130:1777 CLOSE_WAIT TCP 65.96.132.163:22 193.55.113.140:35861 CLOSE_WAIT TCP 65.96.132.163:25 204.127.198.37:40365 CLOSE_WAIT TCP 65.96.132.163:25 216.148.227.85:41320 CLOSE_WAIT TCP 65.96.132.163:110 65.114.186.130:4874 CLOSE_WAIT <snip, it goes on>
Sockets stay in CLOSE_WAIT forever on Win 95/98/Me due to the bug http://support.microsoft.com/default.aspx?scid=kb;EN-US;q229658 Please read that page to understand what follows. Typical server application code looks like this: sock = socket() bind(sock) listen(sock) while (1) { select() newsock = accept(sock) pid = fork() if (pid == 0) { close(sock) child works } if (pid > 0) close(newsock) } Because newsock is closed in the parent before being closed in the child, it stays in CLOSE_WAIT until the parent exits. Not good in server applications. Fixing the application ********************** To keep sock open in the parent, the ported application structure can be changed to: int oldsocks[2^32]; /* I'll be smarter */ sock = socket() (1) bind(sock) listen(sock) while (1) { select() newsock = accept(sock) pid = fork() if (pid == 0) { close(sock) (2) child works } if (pid > 0) { oldsocks[pid] = newsock <= (3) } } sigchild_handler() { pid = waitpid() close(oldsocks[pid]) (4) } The itch is that oldsocks[pidA] remains open in the parent, thus cygwin will duplicate it in a child pidB when there is another accept() and fork(). The socket of pidA will then remain in CLOSE_WAIT if pidA terminates before pidB... Experience shows that CLOSE_WAIT can occur even if pidB closes its copy (but does not terminate) before pidA terminates. Help from cygwin **************** The itch can be cured by adding to cygwin a "close_on_fork" call and using it on line (3) above. This "close_on_fork" applies only to sockets and simply sets a flag. When the flag is set the socket is not duplicated in the parent and it is closed in the child (during fixups). The easiest way to implement this is with fcntl(fd,F_SETCF,flag) where "F_SETCF" is a newly defined command and "flag" is unused. Calling it with non-socket fd's returns an error. See Changelog and diffs below. Related items ************* Adding shutdown() before line (4) has also proved necessary in some cases. Not sure why. Weird behavior (details on request) can also be avoided by "closing on fork" the main sock after line (1) and deleting line (2). In this situation the "linger on close" hack is unnecessary and potentially harmful. I added a test in fhandler_socket::close(). I have ported two servers, exim (an MTA)and qpopper. With those fixes they seem to run fine on all Windows platforms I have tried (98, Me, NT). inetd could be similarly patched (IMHO) but I don't find the Cygwin sources. Similar CLOSE_WAIT issues have been reported with Apache on Win2000. http://sources.redhat.com/ml/cygwin/2001-10/msg01171.html I have no idea if this patch can help there. Problems with duplicate LISTEN have also been reported by me and others http://sources.redhat.com/ml/cygwin/2002-01/msg01579.html http://sources.redhat.com/ml/cygwin/2002-04/msg00515.html No progress there, it's mind boggling. My problem occurs only when the server re-execs itself while a child is running. "close on fork" doesn't seem to help. Pierre ************************************************************************* ************************************************************************* Changelog 2002-04-14 Pierre Humblet <[EMAIL PROTECTED]> * fhandler.h: define FH_CLOFORK, set_close_on_fork_flag() and get_close_on_fork(). * fhandler_socket.cc: (fhandler_socket::fcntl): Add FD_SETCF case. (fhandler_socket::close): test with get_close_on_fork(). * dtable.cc: (dtable::fixup_before_fork) Handle close on fork. (dtable::fixup_after_fork) Ditto. diff -ut ./dtable.cc ../dtable.cc --- ./dtable.cc Thu Apr 11 18:38:28 2002 +++ ../dtable.cc Wed Apr 10 00:10:42 2002 @@ -534,7 +534,7 @@ SetResourceLock (LOCK_FD_LIST, WRITE_LOCK | READ_LOCK, "fixup_before_fork"); fhandler_base *fh; for (size_t i = 0; i < size; i++) - if ((fh = fds[i]) != NULL) + if ((fh = fds[i]) != NULL && !fh->get_close_on_fork ()) { debug_printf ("fd %d (%s)", i, fh->get_name ()); fh->fixup_before_fork_exec (target_proc_id); @@ -585,15 +585,20 @@ for (size_t i = 0; i < size; i++) if ((fh = fds[i]) != NULL) { - if (fh->get_close_on_exec () || fh->get_need_fork_fixup ()) - { - debug_printf ("fd %d (%s)", i, fh->get_name ()); - fh->fixup_after_fork (parent); + if (fh->get_close_on_fork()) + release (i); + else + { + if (fh->get_close_on_exec () || fh->get_need_fork_fixup ()) + { + debug_printf ("fd %d (%s)", i, fh->get_name ()); + fh->fixup_after_fork (parent); + } + if (i == 0) + SetStdHandle (std_consts[i], fh->get_io_handle ()); + else if (i <= 2) + SetStdHandle (std_consts[i], fh->get_output_handle ()); } - if (i == 0) - SetStdHandle (std_consts[i], fh->get_io_handle ()); - else if (i <= 2) - SetStdHandle (std_consts[i], fh->get_output_handle ()); } } diff -ut ./fhandler.h ../fhandler.h --- ./fhandler.h Sun Apr 14 14:19:00 2002 +++ ../fhandler.h Sun Apr 14 14:21:22 2002 @@ -207,6 +207,10 @@ bool get_close_on_exec () { return FHISSETF (CLOEXEC); } int set_close_on_exec_flag (int b) { return FHCONDSETF (b, CLOEXEC); } +#define FH_CLOFORK (FH_FFIXUP|FH_W95LSBUG) + bool get_close_on_fork () { return FHISSETF (CLOFORK) == FH_CLOFORK; } + int set_close_on_fork_flag () { return FHSETF (CLOFORK); } + LPSECURITY_ATTRIBUTES get_inheritance (bool all = 0) { if (all) diff -ut ./fhandler_socket.cc ../fhandler_socket.cc --- ./fhandler_socket.cc Tue Apr 9 22:19:46 2002 +++ ../fhandler_socket.cc Sun Apr 14 11:00:36 2002 @@ -349,7 +349,7 @@ struct linger linger; linger.l_onoff = 1; linger.l_linger = 240; /* seconds. default 2MSL value according to MSDN. */ - setsockopt (get_socket (), SOL_SOCKET, SO_LINGER, + if (!get_close_on_fork()) setsockopt (get_socket (), SOL_SOCKET, SO_LINGER, (const char *)&linger, sizeof linger); while ((res = closesocket (get_socket ())) != 0) @@ -534,6 +534,9 @@ set_flags ((get_flags () & ~O_NONBLOCK_MASK) | new_flags); break; } + case F_SETCF: + set_close_on_fork_flag (); + break; default: res = fhandler_base::fcntl (cmd, arg); break; ************************************************************************* ************************************************************************* Changelog 2002-04-14 Pierre Humblet <[EMAIL PROTECTED]> * libc/include/sys/fcntl.h: Define FD_SETCF flag. --- ./fcntl.h.in Mon Feb 25 10:16:32 2002 +++ ./fcntl.h Sat Apr 6 06:56:42 2002 @@ -124,6 +124,9 @@ #define F_CNVT 12 /* Convert a fhandle to an open fd */ #define F_RSETLKW 13 /* Set or Clear remote record-lock(Blocking) */ #endif /* !_POSIX_SOURCE */ +#ifdef __CYGWIN__ +#define F_SETCF 14 /* Set close on fork, only for sockets */ +#endif /* fcntl(2) flags (l_type field of flock structure) */ #define F_RDLCK 1 /* read lock */
