node-usb-issue-418-delay-at-exit

Reproducing an issue where exiting a program after using node-usb v1.7.0 is significantly delayed.

Behavior differs between versions of node-usb as well as between versions of Node.js.

v1.6.5: no delay.
v1.7.0: significant delay (several seconds, or even infinite).

Timing summary:

	v12.22.1	v14.16.1	v16.0.0
v1.6.5	50 ms	50 ms	50 ms
v1.7.0	8000 ms	8000 ms	∞

The sample size is small, but the difference between “no delay” (less than 100 milliseconds execution time), “long delay” (8-9 seconds), and “does not exit” (several minutes at least) is noticeable on a human scale.

Note that the program code in index.js itself may have bugs. It is essentially a boiled-downed version of the USB Video Class (UVC) device configurator uvcc command line interface, where the issue was first reported.

See

https://github.com/tessel/node-usb/issues/418
https://github.com/joelpurra/uvcc/issues/16

Steps to verify

# NOTE: installing the specific problematic version.
npm install --no-save usb@=1.7.0

# NOTE: you can skip using "time" since the delay is noticeable on a human scale.
time node index.js

Sample output (node-usb v1.7.0, Node.js v16.0.0)

```shell node --version ``` ```text v16.0.0 ``` ```shell time node index.js ``` ```text { idVendor: 1133, idProduct: 2093, deviceAddress: 3, iProduct: '"HD Pro Webcam C920"' } { whiteBalanceTemperature: 4144 } ^C node index.js 0.05s user 0.00s system 0% cpu 1:02.88 total ``` The terminal output is shown immediatelly, but the program has to be forced to stop with ctrl+c.

Test setup

Node.js versions were selected using [`n`](https://github.com/tj/n) (yes, it's a single character name). ```shell n latest ``` ```text installed : v16.0.0 to /home/joelpurra/.n/bin/node active : v16.0.0 at /usr/local/bin/node ``` --- Verified on Ubuntu 20.10. ```shell uname --all ``` ```text Linux Computer 5.4.0-72-generic #80-Ubuntu SMP Mon Apr 12 17:35:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux ``` --- Verified on macOS 10.14 (Mojave). ```shell uname -a ``` ```text Darwin Computer 18.7.0 Darwin Kernel Version 18.7.0: Tue Jan 12 22:04:47 PST 2021; root:xnu-4903.278.56~1/RELEASE_X86_64 x86_64 ```

Workaround

Run the steps above to verify that the code crashes.
Switch to node-usb v1.6.5.
Verify that it works.

# NOTE: clean up.
rm --recursive node_modules/

# NOTE: installing the specific working version.
npm install --no-save usb@=1.6.5

time node index.js