fix qtconsole support

[stevengj]

Currently, if you try to connect to a qtconsole, the kernel hangs while waiting for the first message (normally, it gets an execute_request right away).

Specifically, it gets the identity header of the first message, and ZMQ indicates that more is to come, but then the next recv hangs (which @minrk says should not be possible if ZMQ said there was more of the message).

This could be a bug in our ZMQ wrappers, possibly with the asynchronous stuff that @loladiro recently added. ping @aviks.

[Keno]

The way I'm determining whether or not we can read a message is to query the socket for POLLIN, does ZMQ have a different status to indicate that there a partial message still pending?

[minrk]

ZeroMQ should never report a partial message - multipart messages are sent and received atomically (where by message I mean a sequence of zmq_mst_t frames associated by ZMQ_MORE/RCVMORE/SNDMORE). That is, if getsockopt(socket, ZMQ_RCVMORE) gives True (and the returncode is zero indicating a successful call), the next zmq_msg_recv(socket) is guaranteed not to block. If this condition is indeed being violated, there is a serious bug in zeromq, but that would surprise me.

[Keno]

Alright, I adjusted ZMQ.jl, @stevengj I have verified that this works for me with qtconsole (at least past where it used to hang).

[stevengj]

Okay, it gets farther now. After commit f1da940 (adding the missing history_request), qtconsole successfully starts and evaluates Julia expressions. Remaining problems:

• The --profile option doesn't work, because qtconsole doesn't know how to start the Julia kernel (probably @StefanKarpinski needs to patch it similar to how he patched the notebook). You have to start the Julia kernel and then connect a qtconsole to it with the --existing option.
• Input is received and computed, and a pyout message is sent, but qtconsole is not displaying any output (there are no Out lines). Not sure what is going on here.

[Carreau]

You shouldn't need to patch, try if the following works :

ipython qtconsole --KernelManager.kernel_cmd='["julia", "kernel.jl", "{connection_file}"]'

if it does then it means you shoudl also set c.KernelManager.kernel_cmd='["ruby", "lib/kernel.rb", "{connection_file}"]' in qtconsole config file.

[Carreau]

... file that would be ipython_qtconsole_config.py, probably in .ipyton/profile_julia. alternatively you shoudl be able to set c.KernelManager.kernel_cmd=... in ipython_config.py that should apply to both qtconsole and notebook.

IIRC config take precedence in this order : command line flag > --config=configfile > ipython_config_(qtconsole|notebook) > ipython_config.py> hardcoded defaults. Does it makes sens ?

[stevengj]

Thanks, adding

c.KernelManager.kernel_cmd = ["julia", "/....path..../julia-ipython/jlkernel/kernel.jl", "{connection_file}"]

fixed the --profile for me; I didn't realize that I had only added this to ipython_notebook_config.py

[stevengj]

Okay, basic qtconsole functionality seems to work now. (qtconsole expected an (undocumented) metadata field in pyout messages).