[zeromq-dev] Clean exit in clrzmq. C# "using" vs close (disposal of ZmqContext hangs)

[Robert Hauser]

I noticed weird behavior running the zguide C# lpClient.cs example with no server running. After finishing retries it would hang (during disposing ZmqContext) instead of exit. A reduced case that behaves the same is below.

        public static void Main(string[] args)
        {
            using (ZmqContext context = ZmqContext.Create())   //FIX1 ZmqContext context = ZmqContext.Create();
            {
                var client = context.CreateSocket(SocketType.REQ); //FIX2 using (var client = context.CreateSocket(SocketType.REQ)) { }

                //FIX3 client.Close(); 
                Console.WriteLine("end using");
            } 
            Console.WriteLine("exit");
        }

Any one of replacing lines at FIX1, FIX2, or inserting FIX3 behave better. FIX1 still results in a blocking infinite timeout down in libzmq but it moved it off the main thread to the GC thread which was enough to let the program exit, it seems.

If the original lpClient.cs is not correct, what is the right approach ... to explicitly call Close() on a C# ZmqSocket? Or is the GC for an abandoned ZmqSocket supposed to handle it? Or maybe ZmqContext disposal shouldn't be hanging in this case; this seems doubtful but stack is below (for the code above with no FIX).  -Robert

 	libzmq_d.dll!zmq::signaler_t::wait(int timeout_)  Line 174 + 0x48 bytes	C++
 	libzmq_d.dll!zmq::mailbox_t::recv(zmq::command_t * cmd_, int timeout_)  Line 74 + 0x15 bytes	C++
 	libzmq_d.dll!zmq::ctx_t::terminate()  Line 112 + 0x21 bytes	C++
 	libzmq_d.dll!zmq_ctx_destroy(void * ctx_)  Line 173 + 0xa bytes	C++
 	[External Code]	
 	clrzmq.dll!ZeroMQ.Interop.ContextProxy.Terminate() Line 35 + 0x37 bytes	C#
 	clrzmq.dll!ZeroMQ.Interop.ContextProxy.Dispose(bool disposing) Line 73 + 0xa bytes	C#
 	clrzmq.dll!ZeroMQ.Interop.ContextProxy.Dispose() Line 65 + 0x16 bytes	C#
 	clrzmq.dll!ZeroMQ.ZmqContext.Dispose(bool disposing) Line 186 + 0x22 bytes	C#
 	clrzmq.dll!ZeroMQ.ZmqContext.Dispose() Line 172 + 0x16 bytes	C#
 	lpClient.exe!lpClient.lpClient.Main(string[] args) Line 31 + 0x4e bytes	C#


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