Fix file cache concurrency

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Fixed
+- Fixes a race condition in the file cache service (see #420)
 
 ## [0.1.0]
 ### Added

package.json

@@ -63,7 +63,8 @@
       "new-cap": "off",
       "@typescript-eslint/no-unused-vars": "off",
       "@typescript-eslint/no-unused-vars-experimental": "error",
-      "@typescript-eslint/prefer-readonly-parameter-types": "off"
+      "@typescript-eslint/prefer-readonly-parameter-types": "off",
+      "@typescript-eslint/no-implicit-any-catch": "off"
     }
   },
   "husky": {

src/services/file-cache.ts

@@ -5,9 +5,12 @@ import sequelize from 'sequelize';
 import {FileCache} from '../models/index.js';
 import {TYPES} from '../types.js';
 import Config from './config.js';
+import PQueue from 'p-queue';
+import debug from '../utils/debug.js';
 
 @injectable()
 export default class FileCacheProvider {
+  private static readonly evictionQueue = new PQueue({concurrency: 1});
   private readonly config: Config;
 
   constructor(@inject(TYPES.Config) config: Config) {
@@ -58,10 +61,14 @@ export default class FileCacheProvider {
       const stats = await fs.stat(tmpPath);
 
       if (stats.size !== 0) {
-        await fs.rename(tmpPath, finalPath);
-      }
+        try {
+          await fs.rename(tmpPath, finalPath);
 
-      await FileCache.create({hash, bytes: stats.size, accessedAt: new Date()});
+          await FileCache.create({hash, bytes: stats.size, accessedAt: new Date()});
+        } catch (error) {
+          debug('Errored when moving a finished cache file:', error);
+        }
+      }
 
       await this.evictOldestIfNecessary();
     });
@@ -80,13 +87,19 @@ export default class FileCacheProvider {
   }
 
   private async evictOldestIfNecessary() {
-    const [{dataValues: {totalSizeBytes}}] = await FileCache.findAll({
-      attributes: [
-        [sequelize.fn('sum', sequelize.col('bytes')), 'totalSizeBytes'],
-      ],
-    }) as unknown as [{dataValues: {totalSizeBytes: number}}];
+    void FileCacheProvider.evictionQueue.add(this.evictOldest.bind(this));
+
+    return FileCacheProvider.evictionQueue.onEmpty();
+  }
 
-    if (totalSizeBytes > this.config.CACHE_LIMIT_IN_BYTES) {
+  private async evictOldest() {
+    debug('Evicting oldest files...');
+
+    let totalSizeBytes = await this.getDiskUsageInBytes();
+    let numOfEvictedFiles = 0;
+    // Continue to evict until we're under the limit
+    /* eslint-disable no-await-in-loop */
+    while (totalSizeBytes > this.config.CACHE_LIMIT_IN_BYTES) {
       const oldest = await FileCache.findOne({
         order: [
           ['accessedAt', 'ASC'],
@@ -96,22 +109,111 @@ export default class FileCacheProvider {
       if (oldest) {
         await oldest.destroy();
         await fs.unlink(path.join(this.config.CACHE_DIR, oldest.hash));
+        debug(`${oldest.hash} has been evicted`);
+        numOfEvictedFiles++;
       }
 
-      // Continue to evict until we're under the limit
-      await this.evictOldestIfNecessary();
+      totalSizeBytes = await this.getDiskUsageInBytes();
+    }
+    /* eslint-enable no-await-in-loop */
+
+    if (numOfEvictedFiles > 0) {
+      debug(`${numOfEvictedFiles} files have been evicted`);
+    } else {
+      debug(`No files needed to be evicted. Total size of the cache is currently ${totalSizeBytes} bytes, and the cache limit is ${this.config.CACHE_LIMIT_IN_BYTES} bytes.`);
     }
   }
 
   private async removeOrphans() {
+    // Check filesystem direction (do files exist on the disk but not in the database?)
     for await (const dirent of await fs.opendir(this.config.CACHE_DIR)) {
       if (dirent.isFile()) {
         const model = await FileCache.findByPk(dirent.name);
 
         if (!model) {
+          debug(`${dirent.name} was present on disk but was not in the database. Removing from disk.`);
           await fs.unlink(path.join(this.config.CACHE_DIR, dirent.name));
         }
       }
     }
+
+    // Check database direction (do entries exist in the database but not on the disk?)
+    for await (const model of this.getFindAllIterable()) {
+      const filePath = path.join(this.config.CACHE_DIR, model.hash);
+
+      try {
+        await fs.access(filePath);
+      } catch {
+        debug(`${model.hash} was present in database but was not on disk. Removing from database.`);
+        await model.destroy();
+      }
+    }
+  }
+
+  /**
+   * Pulls from the database rather than the filesystem,
+   * so may be slightly inaccurate.
+   * @returns the total size of the cache in bytes
+   */
+  private async getDiskUsageInBytes() {
+    const [{dataValues: {totalSizeBytes}}] = await FileCache.findAll({
+      attributes: [
+        [sequelize.fn('sum', sequelize.col('bytes')), 'totalSizeBytes'],
+      ],
+    }) as unknown as [{dataValues: {totalSizeBytes: number}}];
+
+    return totalSizeBytes;
+  }
+
+  /**
+   * An efficient way to iterate over all rows.
+   * @returns an iterable for the result of FileCache.findAll()
+   */
+  private getFindAllIterable() {
+    const limit = 50;
+    let previousCreatedAt: Date | null = null;
+
+    let models: FileCache[] = [];
+
+    const fetchNextBatch = async () => {
+      let where = {};
+
+      if (previousCreatedAt) {
+        where = {
+          createdAt: {
+            [sequelize.Op.gt]: previousCreatedAt,
+          },
+        };
+      }
+
+      models = await FileCache.findAll({
+        where,
+        limit,
+        order: ['createdAt'],
+      });
+
+      if (models.length > 0) {
+        previousCreatedAt = models[models.length - 1].createdAt as Date;
+      }
+    };
+
+    return {
+      [Symbol.asyncIterator]() {
+        return {
+          async next() {
+            if (models.length === 0) {
+              await fetchNextBatch();
+            }
+
+            if (models.length === 0) {
+              // Must return value here for types to be inferred correctly
+              return {done: true, value: null as unknown as FileCache};
+            }
+
+            return {value: models.shift()!, done: false};
+          },
+        };
+      },
+    };
   }
 }