Threading or not

[Bruce Sherwood]

Since I've posted ill-formed questions several times I'd like to pay patient readers back by describing a successful answer to something that might affect others.

In Jupyter VPython (see vpython.org) data is sent from a Python program to a JavaScript program and is processed by the GlowScript WebGL library to display 3D animations in the notebook. There are restrictions on sending data from a Python thread, and I even found a disastrous case where early data sent from within a Python thread arrived in the browser after later data sent from outside that thread, yet there seemed no way to avoid the necessity of a thread that would interrupt and send data about 30 times per second.

A robust solution turned out to be the following: The JavaScript program sends an event to Python, which calls a Python program that sends data (if any) to the JavaScript program and in all cases sends a message requesting that the JavaScript program set a timer to send Python another event 1/30th of a second from now. In that way there is no thread in the Python program, so data transmissions are not sent from within a Python thread. 

One might think that the JavaScript program could set an interval timer to send the wakeup message regularly to Python. However, when I tried that scheme it turned out to be very difficult to rerun or kill a program. Apparently killing the kernel doesn't stop JavasScript timeouts. Doing the full roundtrip handshake assures that the JavaScript program will not keep running if the Python program is killed.

[Lawrence D’Oliveiro]

On Wednesday, September 28, 2016 at 6:49:59 PM UTC+13, Bruce Sherwood wrote:

Apparently killing the kernel doesn't stop JavasScript timeouts.

JavaScript runs entirely in the browser.

[Bruce Sherwood]

Certainly, JavaScript runs in the browser, but I think I had the naive notion that having started the JavaScript from Python there would be some mechanism built into the Juptyer machinery that would/could stop the client code. Is there such a mechanism?

[Thomas Kluyver]

On 28 September 2016 at 15:55, Bruce Sherwood <bruce.s...@gmail.com> wrote:

Certainly, JavaScript runs in the browser, but I think I had the naive notion that having started the JavaScript from Python there would be some mechanism built into the Juptyer machinery that would/could stop the client code. Is there such a mechanism?

There is not!