Cloud Sync (google_drive): concurrent folder creation creates duplicate same-name folders; files split between twins and sync stalls

Is there an existing issue for this?

• This is a bug in RetroArch frontend
• I have searched the existing issues

Description

The google_drive cloud sync backend creates duplicate sibling folders with identical names when multiple uploads targeting the same missing folder run concurrently. Google Drive permits same-named siblings, so both "check missing → create" calls succeed. Because folder lookup requests only one match (&fields=files(id)&pageSize=1 in the folder lookup), subsequent syncs non-deterministically resolve to either twin — files end up split across both, the manifest disagrees with whichever twin is consulted, and sync sessions stall (persistent "Cloud Sync in progress 0%").

Evidence (Drive API createdTime metadata from an affected account)

Duplicate twins were created 41–148 ms apart, on three separate dates, including with the 2026-07-22 nightly — so the race is alive in master:

Folder (parent)	Twin 1 created	Twin 2 created	Δ
config (RetroArch/)	2026-06-23T10:57:26.008Z	2026-06-23T10:57:26.049Z	41 ms
Azahar (saves/)	2026-06-24T19:53:13.860Z	2026-06-24T19:53:13.903Z	43 ms
Mupen64Plus-Next (config/)	2026-07-22T05:08:51.723Z	2026-07-22T05:08:51.849Z	126 ms
remaps (config/)	2026-07-22T05:09:02.651Z	2026-07-22T05:09:02.799Z	148 ms

Observed consequences on the same account: FinalBurn Neo, Mesen, melonDS DS, Mupen64Plus-Next core config folders exist in both config twins with contents split between them; sync sessions stall at 0%; one crash occurred immediately after completing the OAuth device flow on Android (1.22.2 nightly 2026-07-22, aarch64) — plausibly the same manifest/folder-tree confusion, though not yet isolated.

Environment

• RetroArch 1.22.2 nightly (2026-07-22), Android aarch64, google_drive backend
• Duplicates also created by late-June 2026 nightlies (see table)
• Sync: Saves + Configuration Files enabled (initially also Thumbnails/System)

Reproduction

1. Fresh Drive account (or empty RetroArch folder), google_drive backend
2. Enable sync for saves + configs with content across many per-core subfolders
3. Trigger the first "Sync Now" so many uploads with missing parent folders run concurrently
4. Inspect Drive: duplicate same-named sibling folders appear (ms apart)

Suggested direction

Serialize folder resolution/creation (single-flight per path via the folder cache added in "cloud sync: allocate the drive folder cache on first use"), or pre-resolve/create the folder tree before enqueueing file transfers. Detecting existing same-name siblings during lookup (pageSize>1 + warn/merge) would also make the backend self-healing for already-affected accounts.

Happy to test patches on affected devices.

Transparency: this report was investigated and drafted with AI assistance (Claude); the evidence is from my own Google Drive account.

Expected behavior

Each folder name should exist exactly once per parent; files should upload into a single canonical folder tree, and sync should complete to a consistent state across devices.

Steps to reproduce the bug

1. Use the google_drive Cloud Sync backend against a fresh Drive account (or empty RetroArch folder)
2. Enable sync for saves + configuration files, with content spread across many per-core subfolders
3. Trigger the first "Sync Now" so many uploads with missing parent folders run concurrently
4. Inspect the Drive folder tree (web UI or API): duplicate same-named sibling folders appear, created milliseconds apart; on later syncs, files split between the twins and sync sessions stall at 0%

Version/Commit

1.22.2 nightly 2026-07-22 (Android aarch64); duplicates also produced by late-June 2026 nightlies

Bisect Results

No response

Present in the nightly version

Yes, this is reproduced in the nightly build

Platform & operating system

Android 14, aarch64 (phone/tablet; multiple devices affected)

Affected Cores

No response

Environment information

No response

Relevant log output

Start by tracing the google_drive backend's concurrent folder lookup and creation, including the folder cache added by "cloud sync: allocate the drive folder cache on first use." Reproduce an initial sync with many missing per-core folders, then verify that each parent has one same-named child, files use one canonical tree, and sync completes consistently.