Watcher backends: merge 'add' and 'change' events into 'touch' #1417
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Summary: Pull Request resolved: #1417 Refactor watcher backends so that they're not required to disambiguate "add" file events from "change" file events, instead emitting ambiguous "touch" events. This distinction isn't typically available from the host OS (`fsevents`, `ReadDirectoryChangesW`, `inotify`), so for the backends to supply it, they must track all files to know whether they existed prior to the OS event. Watchman does this by design anyway, and typically only once per session, but both our `FSEventsWatcher` and `NodeWatcher` currently crawl the whole directory tree and keep an in-memory list of files, and must do so on each Metro start. We don't need this information from the watchers anyway, because we can already infer new vs modified according to whether the file is present in `TreeFS` (ie, from the crawl, or subsequent event). Therefore we *don't* need to reduce the granularity of `metro-file-map`'s *public* events, only the internal ones. By simplifying this, we can follow up by taking a huge burden off the watcher backends. Changelog: Internal Differential Revision: D67579233
Summary: Refactor watcher backends so that they're not required to disambiguate "add" file events from "change" file events, instead emitting ambiguous "touch" events. This distinction isn't typically available from the host OS (`fsevents`, `ReadDirectoryChangesW`, `inotify`), so for the backends to supply it, they must track all files to know whether they existed prior to the OS event. Watchman does this by design anyway, and typically only once per session, but both our `FSEventsWatcher` and `NodeWatcher` currently crawl the whole directory tree and keep an in-memory list of files, and must do so on each Metro start. We don't need this information from the watchers anyway, because we can already infer new vs modified according to whether the file is present in `TreeFS` (ie, from the crawl, or subsequent event). Therefore we *don't* need to reduce the granularity of `metro-file-map`'s *public* events, only the internal ones. By simplifying this, we can follow up by taking a huge burden off the watcher backends. Changelog: Internal Reviewed By: blakef Differential Revision: D67579233
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Summary:
Refactor watcher backends so that they're not required to disambiguate "add" file events from "change" file events, instead emitting ambiguous "touch" events.
This distinction isn't typically available from the host OS (
fsevents,ReadDirectoryChangesW,inotify), so for the backends to supply it, they must track all files to know whether they existed prior to the OS event. Watchman does this by design anyway, and typically only once per session, but both ourFSEventsWatcherandNodeWatchercurrently crawl the whole directory tree and keep an in-memory list of files, and must do so on each Metro start.We don't need this information from the watchers anyway, because we can already infer new vs modified according to whether the file is present in
TreeFS(ie, from the crawl, or subsequent event). Therefore we don't need to reduce the granularity ofmetro-file-map's public events, only the internal ones.By simplifying this, we can follow up by taking a huge burden off the watcher backends.
Changelog: Internal
Differential Revision: D67579233