Fix segmentation fault on linux when calling stopMonitoring()

[mrsch]

udev_monitor_unref was called while cbWork was still accessing the monitor.
Fixed by moving to cbAfter.

Resolves #57

[mrsch]

I added a cleanup hook to automatically stop monitoring and free the udev monitor when node exits.

[MadLittleMods]

Sorry for the delay @mrsch 🙇

I'm unable to build on macOS and Node.js v12.16.2:

$ npm run rebuild

> [email protected] rebuild /Users/eric/Documents/github/node-usb-detection
> node-gyp rebuild

  CXX(target) Release/obj.target/detection/src/detection.o
../src/detection.cpp:224:9: warning: 'AtExit' is deprecated: Use the three-argument variant of AtExit() or AddEnvironmentCleanupHook()
      [-Wdeprecated-declarations]
                node::AtExit(CleanupDetection);
                      ^
/Users/eric/Library/Caches/node-gyp/12.16.2/include/node/node.h:700:1: note: 'AtExit' has been explicitly marked deprecated here
NODE_DEPRECATED(
^
/Users/eric/Library/Caches/node-gyp/12.16.2/include/node/node.h:101:20: note: expanded from macro 'NODE_DEPRECATED'
    __attribute__((deprecated(message))) declarator
                   ^
1 warning generated.
  CXX(target) Release/obj.target/detection/src/deviceList.o
  CXX(target) Release/obj.target/detection/src/detection_mac.o
  SOLINK_MODULE(target) Release/detection.node

[MadLittleMods]

Actually looks successful but just a warning about deprecation. I'm doing some Google'ing to see what the new thing to use is.

[MadLittleMods]

I'm not finding that much info about node::AtExit

It looks like it is supported in Node.js v10.x https://nodejs.org/docs/latest-v10.x/api/addons.html#addons_atexit_hooks

But then looking at Node.js v12 docs, it disappeared and I don't see in the deprecated API docs

In the Node.js v12 changelog, I see (SEMVER-MINOR) src: deprecate two- and one-argument AtExit() (Anna Henningsen) [#30227](https://github.com/nodejs/node/pull/30227)

From the warning, it says warning: 'AtExit' is deprecated: Use the three-argument variant of AtExit() or AddEnvironmentCleanupHook(). Wish I could find some documentation and examples around this.

I sorta see an example here

• https://github.com/nodejs/node/blob/074730081db3269fc3559598c0698a9f6b7b20c2/doc/guides/writing-tests.md#adding-a-new-test

[MadLittleMods]

It seems like AddEnvironmentCleanupHook is the more favored option nowadays according to usage in the docs, https://nodejs.org/docs/latest-v12.x/api/addons.html

@mrsch What was the reason for switching away? dd4a240

[MadLittleMods]

Closing but willing to re-open when responding