feat(client): mechanism for closing and reopening a client and its underlying stores

[stefanceriu]

This patch exposes the pause/resume mechanism for SDK stores all the way up to the FFI Client, so apps can temporarily release SQLite resources when moving to the background and re-acquire them on resume.

The main use case is iOS backgrounding, where keeping SQLite file descriptors and locks open can contribute to 0xdead10cc terminations by the operating system.

The main change are limited to the sqlite crate with in memory stores no-oping trough the default trait implementations:

• a new type called SqliteConnections has been introduced which now holds a store's read connection pools as well as the always on write connection. This lives as an optional on each store's level and gets set to None whenever the store is paused
• during the pausing phase SqliteConnections (through its pause_connections method) does the following:
  • closes the read pool, directly dropping idle connections
  • waits for in flight writes to finish
  • tries a best effort WAL checkpoint
  • drops the write connection on a blocking thread
  • and waits for in-flight read connections to drain
  • this is all best effort with an eventual timeout
• resuming connections is also shared between the stores through SqliteConnections and consists in building a new pool with the previous configuration and creating a new write connection

Handles #6366

Event with this in place though the client side isn't entirely straight forward as the sync service, send queue and pause/resume mechanisms still need to be coordinator in the right order. A better solution would be the to incorporate all of those within an app specific service on the rust side (which we've talked about multiple times over the years) and let the SDK coordinate them instead.

[codecov]

Codecov Report

❌ Patch coverage is 89.62868% with 81 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.94%. Comparing base (7f01cfc) to head (9f70dba).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-sqlite/src/media_store.rs	92.85%	11 Missing and 2 partials ⚠️
crates/matrix-sdk-sqlite/src/event_cache_store.rs	92.20%	11 Missing and 1 partial ⚠️
crates/matrix-sdk-base/src/client.rs	42.85%	0 Missing and 8 partials ⚠️
crates/matrix-sdk-crypto/src/store/memorystore.rs	0.00%	8 Missing ⚠️
crates/matrix-sdk-sqlite/src/connection.rs	84.31%	6 Missing and 2 partials ⚠️
crates/matrix-sdk-sqlite/src/crypto_store.rs	96.12%	0 Missing and 5 partials ⚠️
crates/matrix-sdk-sqlite/src/state_store.rs	96.96%	2 Missing and 3 partials ⚠️
...rix-sdk-base/src/event_cache/store/memory_store.rs	0.00%	4 Missing ⚠️
...es/matrix-sdk-base/src/media/store/memory_store.rs	0.00%	4 Missing ⚠️
crates/matrix-sdk-base/src/store/memory_store.rs	0.00%	4 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6495      +/-   ##
==========================================
+ Coverage   89.92%   89.94%   +0.01%     
==========================================
  Files         381      381              
  Lines      106886   107620     +734     
  Branches   106886   107620     +734     
==========================================
+ Hits        96119    96798     +679     
- Misses       7110     7161      +51     
- Partials     3657     3661       +4     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 9 untouched benchmarks
⏩ 41 skipped benchmarks¹

---

_{Comparing stefan/clientPausing (9f70dba) with main (7f01cfc)}

Footnotes

1. 41 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[andybalaam]

This looks plausible, with one mild suggestion. I don't understand the area well, so feel free to ask someone else for more input if you want it.

[stefanceriu]

Thanks Andy! I'll guess I'll choose... @Hywan as my next victim 😁

[Hywan]

Thanks for the contribution! I made a couple of suggestions, nothing huge.

[Hywan]

Approving ahead of time to save you the last review roundtrip. Thanks for the discussions!