[Sbcl-help] Deadlock with simple client/server sockets application

[Nicholas Mills]

All,

I am trying to write a simple client/server program using
sb-bsd-sockets but I am experiencing deadlock. I am calling
(finish-output) on the stream after each write. The test program is
attached. My program has the following semantics:

Server:
1. Create socket
2. Bind to 127.0.0.1:8675
3. Listen, Accept
4. Read from the client (blocking)
5. Write to the client
6. Cleanup

Client:
1. Create socket
2. Connect to 127.0.0.1:8675
3. Write to the server
4. Read from the server (blocking)
5. Cleanup

I have tested on the following machines:

Machine 1: SBCL 1.0.57, CentOS release 6.2 (Final), Linux
2.6.32-220.17.1.el6.x86_64
Machine 2: SBCL 1.0.38-3.el6, CentOS release 6.3 (Final), Linux
2.6.32-279.1.1.el6.x86_64

I receive the following output:

Server:
$ sbcl --noinform --no-userinit --no-sysinit --load test.lisp --eval
'(server-test :full)'
connected.

Client:
$ sbcl --noinform --no-userinit --no-sysinit --load test.lisp --eval
'(client-test :full)'
connected.
wrote: (10 9 8 Z Y X)


Thank you all,

Nick Mills

[Stig Hemmer]

A bit of testing with READ-CHAR shows that the message has been sent
in full, but that the server hangs on READ.

Apparently READ is expecting something more after the final
)-character of the list. I don't understand why.

However, the problem can be solved by sending a newline character from
the client, using for example TERPRI.

I haven't tested, but you might need to do the same on the server
response. (Though closing the socket *should* satisfy READ)

Good luck!

Stig Hemmer

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