palantir / refreshable

A simple wrapper around a value that changes over time

Refreshable

Simpler wrapper around a value that changes over time

Contributing

For instructions on how to set up your local development environment, check out the CONTRIBUTING.md.

refreshable's Issues

Move implementation to sub-project

Currently is in src/ of the rootProject which is a little funky compared to other repos

N^2 behavior when mapping refreshable

What happened?

We've had a couple instances where we've called Refreshable.map() in a tight loop and it's caused serious problems. The main issues here are:

• map() is a really innocuous sounding name. I map things all the time, why should I be worried about this?
• map() is synchronized, creating a potential bottleneck
• map() copies and for-each's on a data structure every fixed number of invocations. This data structure is also added to on each map(), so the runtime of this is N^2
• N^2 plus mutex equals walking off a cliff very easily

What did you want to happen?

3 possible improvements:

1. delete/deprecate the map() function and direct people to just use subscribe or turn the refreshable into a supplier, or rename the map() function to indicate its heftiness
2. Amortize the N^2 behavior down to linear or move it to be asynchronous somehow
3. Use less heavy-weight concurrency than synchronized/mutex (some form of read-write or non-blocking concurrency)