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[libmicrohttpd] shutdown of listen socket does not work on solaris 10

From: Frank Meier
Subject: [libmicrohttpd] shutdown of listen socket does not work on solaris 10
Date: Fri, 16 Sep 2011 16:15:43 +0200
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I tried to use libmicrohttpd on solaris 10, and my simple programm only starting and stopping the daemon (see below) did hang in. after some investigation (see debug code) I found, that the shutdown call in daemon.c fails, since the daemon socket is not a connected fullduplex but a listening socket. this means the daemon thread keeps hanging in select() and main hangs in pthread_join() (see pstack output). problem is since the socket doesn't get closed, select does not interrupt. After adding CLOSE (fd) after the point of SHUTDOWN () the programm did work. It looks like solaris and linux behave differently when shutdown is called on a listening socket. But on the other hand I'm not sure if it is correct to call shutdown in the first place, since the man page states "The shutdown() call causes all or part of a full-duplex connection on the socket associated with sockfd to be shut down" and the listening socket does not have a connection.

I think the socket should be closed with CLOSE before calling pthread_join() and use SHUTDOWN only on connection sockets.

regards, Frank

/*test programm*/
struct MHD_Daemon* mhdDaemon = 0;
mhdDaemon = MHD_start_daemon (MHD_USE_THREAD_PER_CONNECTION, mhdPort, NULL, NULL, &answer_to_connection, NULL, MHD_OPTION_END);
if (mhdDaemon)
    MHD_stop_daemon (mhdDaemon);  // <-here it hangs
    mhdDaemon = 0;

/*debug code in daemon.c*/
--- daemon/daemon.c     (revision 16873)
+++ daemon/daemon.c     (working copy)
@@ -2477,7 +2477,11 @@
       daemon->worker_pool[i].shutdown = MHD_YES;
       daemon->worker_pool[i].socket_fd = -1;
+       int res = SHUTDOWN (fd, SHUT_RDWR);
+       int tmpErrno = errno;
+       printf("shutdown res:%d  %s\n", res, strerror(tmpErrno));
+       CLOSE (fd);

->output with debug code:
shutdown res:-1  Transport endpoint is not connected

/*pstack output -> damon thread is in select, main hangs in pthread join*/
$ pstack 16802
16802:  ./test.bin
-----------------  lwp# 1 / thread# 1  --------------------
 feee9365 lwp_wait (2, 80478d8)
 feee2c1f _thrp_join (2, 0, 8047918, 1) + 5a
 feee2d9e pthread_join (2, 8047918, feeec7e0, fef9665d) + 2b
 fef96777 MHD_stop_daemon (8060d40, 0, 0, fee63301) + 12b
 0805080a main     (1, 8047988, 8047990) + 6f
 080506ac _start   (1, 8047a88, 0, 8047a93, 8047abe, 8047b78) + 60
-----------------  lwp# 2 / thread# 2  --------------------
 feee8da5 pollsys  (fed5ed50, 1, 0, 0)
 fee93afa pselect  (4, fed5ef30, fed5eeb0, fed5ee30, 0, 0) + 18e
 fee93df0 select   (4, fed5ef30, fed5eeb0, fed5ee30, 0, 0) + 82
fef95ba4 MHD_select (fec50200, fec50200, fed5efec, feee59b9, 8060d40, 0) + 130
 fef96248 MHD_select_thread (8060d40) + 18
 feee59b9 _thr_setup (fec50200) + 4e
 feee5ca0 _lwp_start (fec50200, 0, 0, fed5eff8, feee5ca0, fec50200)

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