The socket selector holds a `seq` of per-descriptor data. When a reader
is registered, a pointer to a seq item is stored - when the `seq` grows,
this pointer becomes dangling and causes crashes like
https://github.com/status-im/nimbus-eth2/issues/3521.
It turns out that there already exist two mechanisms for passing user
data around - this PR simply removes one of them, saving on memory usage
and removing the need to store pointers to the `seq` data that become
dangling on resize.
* exception tracking
This PR adds minimal exception tracking to chronos, moving the goalpost
one step further.
In particular, it becomes invalid to raise exceptions from `callSoon`
callbacks: this is critical for writing correct error handling because
there's no reasonable way that a user of chronos can possibly _reason_
about exceptions coming out of there: the event loop will be in an
indeterminite state when the loop is executing an _random_ callback.
As expected, there are several issues in the error handling of chronos:
in particular, it will end up in an inconsistent internal state whenever
the selector loop operations fail, because the internal state update
functions are not written in an exception-safe way. This PR turns this
into a Defect, which probably is not the optimal way of handling things
- expect more work to be done here.
Some API have no way of reporting back errors to callers - for example,
when something fails in the accept loop, there's not much it can do, and
no way to report it back to the user of the API - this has been fixed
with the new accept flow - the old one should be deprecated.
Finally, there is information loss in the API: in composite operations
like `poll` and `waitFor` there's no way to differentiate internal
errors from user-level errors originating from callbacks.
* store `CatchableError` in future
* annotate proc's with correct raises information
* `selectors2` to avoid non-CatchableError IOSelectorsException
* `$` should never raise
* remove unnecessary gcsafe annotations
* fix exceptions leaking out of timer waits
* fix some imports
* functions must signal raising the union of all exceptions across all
platforms to enable cross-platform code
* switch to unittest2
* add `selectors2` which supercedes the std library version and fixes
several exception handling issues in there
* fixes
* docs, platform-independent eh specifiers for some functions
* add feature flag for strict exception mode
also bump version to 3.0.0 - _most_ existing code should be compatible
with this version of exception handling but some things might need
fixing - callbacks, existing raises specifications etc.
* fix AsyncCheck for non-void T
Eugene Kabanov
Jacek Sieka
Eugene Kabanov
Mamy Ratsimbazafy