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AsyncSave
Moves Valheim's world and character saves off the main thread, so saving no longer freezes the game.
| Date uploaded | 12 hours ago |
| Version | 0.5.0 |
| Download link | MidnightMods-AsyncSave-0.5.0.zip |
| Downloads | 196 |
| Dependency string | MidnightMods-AsyncSave-0.5.0 |
This mod requires the following mods to function
denikson-BepInExPack_Valheim
BepInEx pack for Valheim. Preconfigured with the correct entry point for mods and preferred defaults for the community.
Preferred version: 5.4.2333README
AsyncSave
AsyncSave moves Valheim's world and character saves off the main thread, so a save no longer freezes the game. Nothing about the save format changes — the bytes it writes are the bytes vanilla would have written.
The two halves are independent and neither syncs anything over the network, so the same DLL runs unmodified on a dedicated server, a client, or a host, in any mix of installed and not.
How it works
World save (server or host)
Vanilla's ZNet.SaveWorld clones every ZDO in the world into a fresh list, on one frame, and only
then hands it to the writer thread. AsyncSave replaces that with a coroutine that walks
ZDOMan's sectors across many frames, serializing each ZDO straight into a reusable buffer, while
the writer thread waits on it.
Because the walk now spans frames, the world can change underneath it. Three things keep the result consistent:
- Sector scratch copies. Each sector's live list is copied atomically before iterating, so a removal cannot shift indices out from under the walk.
AddToSectortracking. A ZDO that is created, or that moves into a sector the walk has already passed, is queued and serialized in a catch-up pass at the end. Without this, anything that moved backwards across a sector boundary mid-save would silently vanish from the file.- Revision reconciliation. A ZDO whose data changed after it was serialized is re-encoded in place, so the save is not one revision stale.
The buffer and the dedup table are split into 64 MB segments rather than living in single arrays, because a .NET array cannot exceed 2 GB and a large world needs more than that.
Character save (anywhere there is a local player)
Vanilla's minimap save writes 8.4 million individual booleans through a BinaryWriter, then
gzips the result and writes the .fch synchronously. AsyncSave bulk-copies the explored arrays
(two memcpys producing the identical byte sequence), then hands compression, hashing and the
file write to a background worker. The parts that touch Unity-owned or gameplay-mutated state stay
on the main thread.
Quitting, logging out and shutdown always use the untouched vanilla path, so the last save before the scene goes away is never in flight.
Configuration
BepInEx/config/MidnightsFX.AsyncSave.cfg. All values apply immediately — no restart.
1 - General
| Setting | Default | What it does |
|---|---|---|
| Save interval (seconds) | 1800 |
World autosave period. Left at the vanilla 1800 this is not applied at all, so another mod setting the interval still wins. Below 60 disables vanilla's pre-save warning; the save itself still runs. |
| Logging | Simple |
Off, Simple (one line per save), Detailed (counts and buffer figures), Debug (adds per-phase timings). |
2 - World Save
Server-side only; a pure client ignores this whole section.
| Setting | Default | What it does |
|---|---|---|
| Enabled | true |
Off restores the vanilla save path completely. |
| Async manual saves | true |
Whether the in-game menu's Save button returns immediately or blocks until the world is on disk. The /save console command is already async in vanilla and is unaffected. |
| Slice budget (ms) | 2 |
Ceiling on main-thread time per slice. Lower = smoother frames, longer save. |
| Adaptive budget | true |
Scale each slice to the frame time the game is not already using, so a save costs little while the game is struggling. Off gives a fixed budget and the shortest save. |
| Frame headroom (%) | 25 |
How much longer a frame may take while saving, as a percentage of what it costs without us. 25 means a 4 ms frame may become 5 ms. Ignored when the adaptive budget is off. |
| Reconcile mutations | Dirty |
Dirty re-encodes only what the revision hooks flagged and costs nothing on an idle world. FullScan re-checks every ZDO — correct regardless of hook coverage, but it walks the whole world every save. |
3 - Character Save
| Setting | Default | What it does |
|---|---|---|
| Enabled | true |
Off restores the vanilla character save. |
Automatic stand-downs
If the mod cannot safely run — it fails to patch ZNet.SaveWorld, the .fch layout is not the one
this build was written against, the revision hooks are missing, or the host is big-endian — it
disables the affected half or falls back to FullScan for that session only and logs why. Your
config file is never rewritten, so the setting you chose is still there next launch.
Requirements
BepInEx. No dependencies on other mods. Incompatible with SmoothSave (they patch the same paths); BepInEx will refuse to load both.
CHANGELOG
0.5.0
Rebuild for Deep North!
0.4.0
Prune the server's dead-ZDO table instead of letting it grow for the whole session.
Vanilla records every destroyed ZDO in ZDOMan.m_deadZDOs and only clears it when a world
loads, but reads it for one purpose: rejecting a create for a ZDO that died while a client's
packet was still in flight. On a large world that is millions of retained entries answering a
question about the last few seconds - a dictionary that is rehashed as it grows and walked by
every gen-2 GC.
Entries now expire after a configurable lifetime (default 60s). Pruning is O(expired) with no
scan of the table, and is server-side only.
0.3.0
Initial release.
