Hi,
Over the past week I have been asking some of you how to correct a
hang on exit with TcpChannels on Windows. To recap instantiating a
TcpChannel runs a background thread which calls Socket.Accept and
blocks. During shutdown a call to mono_thread_manage executes an APC
on the waiting thread and then (mono_thread_manage) waits for the
blocking thread to exit. The problem is that the APC call does not
cause the accept call to break.
There were a couple of suggestions about how to solve this problem.
Some were specific to accept and others were general patterns
'un-stick' blocking calls in the runtime. I believe that have tried
them all. Some did not work while others caused other complications.
The one I decided on was to call select with a timeout to determine if
a following accept call would succeed immediately. Consider it a peek
on the socket. If the select times out and no connection is present I
check the thread state for StopRequested. (Not Abort intentionally.)
Finally this is an a infinite loop until a connection is present or
the thread is stopped. The loop is only applicable to Windows as I do
not observe a problem on Linux.
One thing that I had to change was the signature to the internal
accept call. I need to know the blocking state of the socket. If a
socket is in blocking mode I can go into the loop. If the socket is
in non-blocking mode I can not use the loop because it will cause the
call to accept to block on a non-blocking socket. The reason I have
to pass it into the internal call is because after much searching I
can not find a way to query the blocking state of a socket. (There is
no ret = fcntl(fd, F_GETFL, 0); on Windows?) If anyone knows how to
query this state let me know and I will be happy to change it.
-bill
2008-12-17 Bill Holmes <billholme...@gmail.com>
* Socket.cs (Accept_internal) : Changing the signature to pass
the blocking state.
* socket-io.h : Changing the signature of
ves_icall_System_Net_Sockets_Socket_Accept_internal to pass
the blocking state.
* icall-def.h : Changing the signature of
System.Net.Sockets.Socket.Accept_internal to pass the blocking state.
* socket-io.c (ves_icall_System_Net_Sockets_Socket_Accept_internal) :
For Windows only. Avoid blocking when calling accept by
querying for a connection via select. The loop also queries
the thread state every 1000 micro seconds for the thread
stop state. This will avoid the process hanging on shutdown
when using a TcpChannel that is never connected to.
Code is contributed under MIT/X11 license.
Index: mcs/class/System/System.Net.Sockets/Socket.cs
===================================================================
--- mcs/class/System/System.Net.Sockets/Socket.cs (revision 121718)
+++ mcs/class/System/System.Net.Sockets/Socket.cs (working copy)
@@ -1381,7 +1381,7 @@
// Creates a new system socket, returning the handle
[MethodImplAttribute(MethodImplOptions.InternalCall)]
- private extern static IntPtr Accept_internal(IntPtr sock, out int error);
+ private extern static IntPtr Accept_internal(IntPtr sock, out int error, bool blocking);
Thread blocking_thread;
public Socket Accept() {
@@ -1392,7 +1392,7 @@
IntPtr sock = (IntPtr) (-1);
blocking_thread = Thread.CurrentThread;
try {
- sock = Accept_internal(socket, out error);
+ sock = Accept_internal(socket, out error, blocking);
} catch (ThreadAbortException) {
if (disposed) {
#if !NET_2_1
@@ -1425,7 +1425,7 @@
blocking_thread = Thread.CurrentThread;
try {
- sock = Accept_internal (socket, out error);
+ sock = Accept_internal (socket, out error, blocking);
} catch (ThreadAbortException) {
if (disposed) {
#if !NET_2_1
Index: mcs/class/System/System.Net.Sockets/ChangeLog
===================================================================
--- mcs/class/System/System.Net.Sockets/ChangeLog (revision 121718)
+++ mcs/class/System/System.Net.Sockets/ChangeLog (working copy)
@@ -1,4 +1,11 @@
+2008-12-17 Bill Holmes <billholme...@gmail.com>
+
+ * Socket.cs (Accept_internal) : Changing the signature to pass
+ the blocking state.
+
+ Code is contributed under MIT/X11 license.
+
2008-12-03 Gonzalo Paniagua Javier <gonz...@novell.com>
* UdpClient.cs: don't Poll() in Receive(), the call to ReceiveFrom
Index: mono/mono/metadata/socket-io.h
===================================================================
--- mono/mono/metadata/socket-io.h (revision 121718)
+++ mono/mono/metadata/socket-io.h (working copy)
@@ -194,7 +194,7 @@
extern gint32 ves_icall_System_Net_Sockets_SocketException_WSAGetLastError_internal(void) MONO_INTERNAL;
extern gint32 ves_icall_System_Net_Sockets_Socket_Available_internal(SOCKET sock, gint32 *error) MONO_INTERNAL;
extern void ves_icall_System_Net_Sockets_Socket_Blocking_internal(SOCKET sock, gboolean block, gint32 *error) MONO_INTERNAL;
-extern gpointer ves_icall_System_Net_Sockets_Socket_Accept_internal(SOCKET sock, gint32 *error) MONO_INTERNAL;
+extern gpointer ves_icall_System_Net_Sockets_Socket_Accept_internal(SOCKET sock, gint32 *error, gboolean blocking) MONO_INTERNAL;
extern void ves_icall_System_Net_Sockets_Socket_Listen_internal(SOCKET sock, guint32 backlog, gint32 *error) MONO_INTERNAL;
extern MonoObject *ves_icall_System_Net_Sockets_Socket_LocalEndPoint_internal(SOCKET sock, gint32 *error) MONO_INTERNAL;
extern MonoObject *ves_icall_System_Net_Sockets_Socket_RemoteEndPoint_internal(SOCKET sock, gint32 *error) MONO_INTERNAL;
Index: mono/mono/metadata/ChangeLog
===================================================================
--- mono/mono/metadata/ChangeLog (revision 121718)
+++ mono/mono/metadata/ChangeLog (working copy)
@@ -1,3 +1,21 @@
+2008-12-17 Bill Holmes <billholme...@gmail.com>
+
+ * socket-io.h : Changing the signature of
+ ves_icall_System_Net_Sockets_Socket_Accept_internal to pass
+ the blocking state.
+
+ * icall-def.h : Changing the signature of
+ System.Net.Sockets.Socket.Accept_internal to pass the blocking state.
+
+ * socket-io.c (ves_icall_System_Net_Sockets_Socket_Accept_internal) :
+ For Windows only. Avoid blocking when calling accept by
+ querying for a connection via select. The loop also queries
+ the thread state every 1000 micro seconds for the thread
+ stop state. This will avoid the process hanging on shutdown
+ when using a TcpChannel that is never connected to.
+
+ Code is contributed under MIT/X11 license.
+
2008-12-17 Miguel de Icaza <mig...@novell.com>
* icall.c (ves_icall_System_Environment_get_Platform): For
Index: mono/mono/metadata/icall-def.h
===================================================================
--- mono/mono/metadata/icall-def.h (revision 121718)
+++ mono/mono/metadata/icall-def.h (working copy)
@@ -401,7 +401,7 @@
ICALL(NDNS_3, "GetHostName_internal(string&)", ves_icall_System_Net_Dns_GetHostName_internal)
ICALL_TYPE(SOCK, "System.Net.Sockets.Socket", SOCK_1)
-ICALL(SOCK_1, "Accept_internal(intptr,int&)", ves_icall_System_Net_Sockets_Socket_Accept_internal)
+ICALL(SOCK_1, "Accept_internal(intptr,int&,bool)", ves_icall_System_Net_Sockets_Socket_Accept_internal)
ICALL(SOCK_2, "Available_internal(intptr,int&)", ves_icall_System_Net_Sockets_Socket_Available_internal)
ICALL(SOCK_3, "Bind_internal(intptr,System.Net.SocketAddress,int&)", ves_icall_System_Net_Sockets_Socket_Bind_internal)
ICALL(SOCK_4, "Blocking_internal(intptr,bool,int&)", ves_icall_System_Net_Sockets_Socket_Blocking_internal)
Index: mono/mono/metadata/socket-io.c
===================================================================
--- mono/mono/metadata/socket-io.c (revision 121718)
+++ mono/mono/metadata/socket-io.c (working copy)
@@ -811,13 +811,41 @@
}
gpointer ves_icall_System_Net_Sockets_Socket_Accept_internal(SOCKET sock,
- gint32 *error)
+ gint32 *error,
+ gboolean blocking)
{
SOCKET newsock;
MONO_ARCH_SAVE_REGS;
*error = 0;
+
+#ifdef PLATFORM_WIN32
+ /* Several applications are getting stuck during shutdown on Windows
+ * when an accept call is on a background thread.
+ *
+ */
+ if (blocking) {
+ MonoThread* curthread = mono_thread_current ();
+
+ if (curthread) {
+ for (;;) {
+ int selectret;
+ TIMEVAL timeout;
+ fd_set readfds;
+ FD_ZERO (&readfds);
+ FD_SET(sock, &readfds);
+ timeout.tv_sec = 0;
+ timeout.tv_usec = 1000;
+ selectret = select (0, &readfds, NULL, NULL, &timeout);
+ if (selectret > 0)
+ break;
+ if (curthread->state & ThreadState_StopRequested)
+ return NULL;
+ }
+ }
+ }
+#endif
newsock = _wapi_accept (sock, NULL, 0);
if(newsock==INVALID_SOCKET) {
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