Add IDBFS.onAutoPersistStateChanged callback. Fixes flakiness in browser.test_fs_idbfs_sync_autopersist (#26895)

Add IDBFS.onAutoPersistStateChanged callback that can be used to detect
when IDBFS autopersistence operations start and finish.

Fixes test failures in test browser.test_test_fs_idbfs_sync_autopersist,
by giving the persistence logic time to complete before quitting the
first phase of test.

Author: juj

ChangeLog.md

@@ -38,6 +38,9 @@ See docs/process.md for more on how version tagging works.
   binaryen for wasm). (#26677)
 - The `-m64` compiler flag is now honored, and works as an alias for
   `-sMEMORY64` and/or `--target=wasm64`. (#26765)
+- The autopersistence feature in IDBFS mount now supports registering a global
+  callback `IDBFS.onAutoPersistStateChanged = active => {}`, which will be
+  notified of all IDBFS sync start and end events. (#26895)
 
 5.0.7 - 04/30/26
 ----------------

src/lib/libidbfs.js

@@ -18,14 +18,31 @@ addToLibrary({
     DB_VERSION: 21,
     DB_STORE_NAME: 'FILE_DATA',
 
+    // When using the autopersistence mechanism, users can set
+    // IDBFS.onAutoPersistStateChanged callback to receive notification events
+    // for when persistence operations are in-flight. Use the following syntax:
+    /*
+    IDBFS.onAutoPersistStateChanged = autoPersistActive => {
+      if (autoPersistActive) {
+        console.log('IDBFS persistence operation has started.');
+      } else {
+        console.log('IDBFS persistence operation has finished.');
+      }
+    };
+    */
+
     // Queues a new VFS -> IDBFS synchronization operation
     queuePersist: (mount) => {
       function onPersistComplete() {
         if (mount.idbPersistState === 'again') startPersist(); // If a new sync request has appeared in between, kick off a new sync
-        else mount.idbPersistState = 0; // Otherwise reset sync state back to idle to wait for a new sync later
+        else {
+          mount.idbPersistState = 0; // Otherwise reset sync state back to idle to wait for a new sync later
+          IDBFS.onAutoPersistStateChanged?.(false);
+        }
       }
       function startPersist() {
         mount.idbPersistState = 'idb'; // Mark that we are currently running a sync operation
+        IDBFS.onAutoPersistStateChanged?.(true);
         IDBFS.syncfs(mount, /*populate:*/false, onPersistComplete);
       }
 

test/fs/test_idbfs_sync.c

@@ -152,7 +152,24 @@ void test() {
 #endif
 
 #ifdef IDBFS_AUTO_PERSIST
+
+#if FIRST
+  // Register an IDBFS autopersist completion callback to detect when the
+  // filesystem sync operation has finished.
+  EM_ASM({
+    IDBFS.onAutoPersistStateChanged = (autoPersistActive) => {
+      if (autoPersistActive) {
+        console.log('IDBFS persistence operation has started.');
+      } else {
+        console.log('IDBFS persistence operation has finished.');
+        callUserCallback(_finish);
+      }
+    }
+  });
+#else
   finish();
+#endif
+
 #else
   // sync from memory state to persisted and then
   // run 'finish'