Add an in-memory cache of the file list for disk spaces (#1012)

Add an in-memory cache of the file list for disk spaces

common/spaces/disk_space_primitives.ts

@@ -16,6 +16,9 @@ const excludedFiles = ["data.db", "data.db-journal", "sync.json"];
 
 export class DiskSpacePrimitives implements SpacePrimitives {
   rootPath: string;
+  fileListCache: FileMeta[] = [];
+  fileListCacheTime = 0;
+  fileListCacheUpdating: AbortController | null = null;
 
   constructor(rootPath: string) {
     this.rootPath = Deno.realPathSync(rootPath);
@@ -92,6 +95,11 @@ export class DiskSpacePrimitives implements SpacePrimitives {
       }
       file.close();
 
+      // Invalidate cache and trigger an update
+      this.fileListCache = [];
+      this.fileListCacheTime = 0;
+      this.updateCacheInBackground();
+
       // Fetch new metadata
       return this.getFileMeta(name);
     } catch (e) {
@@ -121,11 +129,44 @@ export class DiskSpacePrimitives implements SpacePrimitives {
   async deleteFile(name: string): Promise<void> {
     const localPath = this.filenameToPath(name);
     await Deno.remove(localPath);
+
+    // Invalidate cache and trigger an update
+    this.fileListCache = [];
+    this.fileListCacheTime = 0;
+    this.updateCacheInBackground();
   }
 
   async fetchFileList(): Promise<FileMeta[]> {
+    // console.log("Fetching file list");
+    const startTime = performance.now();
+
+    // If the file list cache is less than 60 seconds old, return it
+    if (
+      this.fileListCache.length > 0 &&
+      startTime - this.fileListCacheTime < 60000
+    ) {
+      // Trigger a background sync, but return the cached list while the cache is being updated
+      this.updateCacheInBackground();
+      return this.fileListCache;
+    }
+
+    // Otherwise get the file list and wait for it
+    const allFiles: FileMeta[] = await this.getFileList();
+
+    const endTime = performance.now();
+    console.info("Fetched uncached file list in", endTime - startTime, "ms");
+
+    this.fileListCache = allFiles;
+    this.fileListCacheTime = startTime;
+
+    return allFiles;
+  }
+
+  private async getFileList(): Promise<FileMeta[]> {
     const allFiles: FileMeta[] = [];
     for await (const file of walkPreserveSymlinks(this.rootPath)) {
+      // Uncomment to simulate a slow-ish disk
+      // await new Promise((resolve) => setTimeout(resolve, 1));
       const fullPath = file.path;
       try {
         const s = await Deno.stat(fullPath);
@@ -149,9 +190,42 @@ export class DiskSpacePrimitives implements SpacePrimitives {
         }
       }
     }
-
     return allFiles;
   }
+
+  private updateCacheInBackground() {
+    if (this.fileListCacheUpdating) {
+      // Cancel the existing background update, so we never return stale data
+      this.fileListCacheUpdating.abort();
+    }
+
+    const abortController = new AbortController();
+    this.fileListCacheUpdating = abortController;
+
+    const updatePromise = this.getFileList().then((allFiles) => {
+      if (abortController.signal.aborted) return;
+
+      this.fileListCache = allFiles;
+      this.fileListCacheTime = performance.now();
+      console.info(
+        "Updated file list cache in background:",
+        allFiles.length,
+        "files found",
+      );
+    }).catch((error) => {
+      if (abortController.signal.aborted) return;
+
+      if (error.name !== "AbortError") {
+        console.error("Error updating file list cache in background:", error);
+      }
+    }).finally(() => {
+      if (this.fileListCacheUpdating === abortController) {
+        this.fileListCacheUpdating = null;
+      }
+    });
+
+    return updatePromise;
+  }
 }
 
 async function* walkPreserveSymlinks(