Zone implementation discussion

[matthewp]

@justinbmeyer today mentioned an alternative implementation. Want to break down the current implementation and compare it to the other, to discuss their strengths and weaknesses.

1. Wrap when each task is run

This is how it is currently implemented. Each time a Task is run we setup the globals and after the Task completes we restore the original values.

Strength

• Since we override on each Task execution, if some other code also overrides a global ours will always "win", meaning we are the outer layer of the onion:

ourSetTimeout(someOtherSetTimeout(realSetTimeout()))

This is important so that we can ensure all Tasks run within a Zone.

Weakness

• This is heavier, lots of properties changing before and after Task execution.
• Code keeping local references defeats us.

  2. Wrap at execution time only

This would be if the wrapping only happen

Strength

• If set up early enough, would handle cases where modules keep local references

  Weakness

• We can't ensure that Tasks run within a Zone because other code might override a global.

  3. Both?

I think this is probably possible, use method 1 to ensure our versions are the outer layer of the onion and method 2 to ensure local references are covered.

[matthewp]

It's possible #2 would work on it's own. Even if code does override globals, it eventually does have to call something asynchronous, so eventually one of our globals would be used (global.Promise might be overridden but underlying that it would use MutationObserver). It's worth giving a shot.

[matthewp]

Closed by #63