[serial] Use a fast path to avoid pattern matching

[joerg1985]

I was wondering why a fresh installed openhab instance without addons was creating ~ 1000 int[] instances every 15s.
This fallout is visible when monitoring the free memory of the instance:

This PR will add a fast path to avoid this fallout from matching a regex against dozens of not matching directories.

Signed-off-by: Jörg Sautter joerg.sautter@gmx.net

[holgerfriedrich]

Good catch, you patch avoids calling the more expensive pattern matching (at least as long as the pattern contains the -.
If I get it correctly, you search for - many times: on the full path and all the parent path strings the way up, as getUsbInterfaceParentPath is called recursively. If you want to avoid that, maybe add a second helper function for the recursive calls, check for the shortcut only once, and then call the helper. WDYT?

[joerg1985]

Yes there is room for improvments, but also the danger of over-engineering.
Usually the matching part is at the end and it does not need to go more than 3 parents up the tree, therefore i think it is okay to check every time.

[joerg1985]

Ps: in the negative case there is no - at all, so it will check only the full path once and return.

[holgerfriedrich]

Agreed. Thank you.

[wborn]

This probably also significantly reduces the CPU consumption by the serial scanner thread? It is the most CPU consuming thread on my system and I still wanted to look into how to reduce this. 🙂

[joerg1985]

@wborn the GC threads are taking a lot of time on my installation, so i am locking where the fallout is coming from and try to fix this. This seems to happen also in some libraries too, e.g. jmdns/jmdns#275