commit | 094c2dd1ca5f267289b34187882b76b6fbde19af | [log] [tgz] |
---|---|---|
author | Yigit Boyar <[email protected]> | Wed Mar 13 15:42:08 2024 -0700 |
committer | Android Build Coastguard Worker <[email protected]> | Fri Mar 15 17:58:05 2024 +0000 |
tree | 0e044da00a501055c2373eb2be14690a079bea00 | |
parent | 1642890cce1bbea6ecf520e6261400e393db20a8 [diff] |
Emit from file observer when the connection is established There is a race condition in our IPC design where if the IPC needs some initialization, DataStore has no way of waiting for that initialization. So when DataStore wants to run logic similar to: 1) start observing IPC 2) read the file 3) wait for IPC upadtes Ideally, DataStore would want to do this to ensure it never misses an update when it is observed, yet it does not have the mechanism wait for IPC to be ready. The only API it has is `Flow<Unit>` from the IPC but it rather needs either: a) Flow<Event>, enum Event{STARTED, CHANGE_DETECTED} or b) suspend fun observe():Flow<Unit> which could return after initialization is complete. b is not super practical because it runs into another problem where the Flow may never be collected. a is the better solution as it provides the state as events and DataStore can wait for STARTED before reading to avoid missing events. Note that Flow.onStart is not an option here because it is called before the contents of the Flow computation starts, hence does not wait for the FileSystem communication. We did in fact hit this problem when writing tests for MP-IPC, hence the internals of it emitted after establishing the connection to the Filesystem but dropped that initial emission in the public API's implementation. This CL makes MP-IPC also dispatch that initial Unit in its public API implementation, which in practice means it will be dispatching a Change notification after it connects to the FileSystem. This does not ensure (2) happens before (1) but it ensures (3) does not miss an event if (2) happens before (1) starts. Note that this does not cause an extra read on the FS if the file didn't change after (2) because we have the version in shared counter so the change should not have a noticable perf impact. Fixes: 326141553 Test: did run it 200 times in P71532587/targets/androidx_device_tests and also 2K times on a local emulator and firebase (matrix-2dop3ihikvsfy). (cherry picked from https://android-review.googlesource.com/q/commit:94002239d3b000874d9dcf11eb6594a5613dd5c9) Merged-In: I38b3f041b09f1332fb6f1bbf0e3bd266750465be Change-Id: I38b3f041b09f1332fb6f1bbf0e3bd266750465be
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