What's ds_map_secure_save?

GameMaker function that encrypts and writes a ds_map to disk. Decryptable only on the same device. Convenient but doesn’t protect against torn writes.

Why does crash corrupt the file?

If the game crashes mid-write, the target file is half-written. Next load reads partial data, fails decryption, throws an error or loads garbage.

What's the atomic write pattern?

Write to save.tmp; on success, rename to save.dat. The rename is atomic on most OSes; either the new file is in place or the old one is. No half-written state visible.

Fix: GameMaker ds_map Secure Save Fails After Crash

Quick answer: Write to a temp file first (save.tmp), then rename via file_rename to the final name. Keep a previous-version backup for fallback.

An RPG saves to slot via ds_map_secure_save. A player’s GPU crashes the game mid-save; on relaunch, “Save corrupted, starting new game”. They lose 10 hours of progress.

Atomic Write

function safe_save(filename, data_map) {
    var tmp = filename + ".tmp";
    ds_map_secure_save(data_map, tmp);
    if (file_exists(filename)) file_delete(filename);
    file_rename(tmp, filename);
}

Three-step: write to .tmp, delete old, rename .tmp to final. Each step is atomic; if the game dies between, either the old or new file is whole, never half-written.

Keep Previous Save as Backup

function safe_save_with_backup(filename, data_map) {
    var tmp = filename + ".tmp";
    var bak = filename + ".bak";

    ds_map_secure_save(data_map, tmp);

    if (file_exists(filename)) {
        if (file_exists(bak)) file_delete(bak);
        file_rename(filename, bak);
    }
    file_rename(tmp, filename);
}

Previous save kept as .bak. Two generations recoverable.

Safe Load

function safe_load(filename) {
    if (file_exists(filename)) {
        var m = ds_map_secure_load(filename);
        if (m != -1) return m;
    }
    // fall back to backup
    var bak = filename + ".bak";
    if (file_exists(bak)) {
        return ds_map_secure_load(bak);
    }
    return undefined;
}

Try primary; on decryption failure (returns -1), try .bak. Players keep most of their progress.

Flush to Disk

On Steam Deck/Switch, OS may buffer writes. After the rename, force a sync if your build target supports it. GameMaker on PC usually flushes immediately.

Verifying

Save, kill the process mid-game (Task Manager). Reload — previous save loads cleanly. Test repeatedly. Then test mid-write kill: previous file should still load via backup path.

“Atomic write + backup = no torn saves. Players forgive a small rollback; they don’t forgive total loss.”

For Steam Cloud Save users, add a checksum file alongside save.dat — lets you detect cloud corruption on download too.