perf(core): implement parallel file processing for 74% performance improvement (#4763)

Co-authored-by: Jacob Richman <jacob314@gmail.com>
Co-authored-by: Sandy Tao <sandytao520@icloud.com>

packages/core/src/tools/read-many-files.test.ts

@@ -477,4 +477,139 @@ describe('ReadManyFilesTool', () => {
       fs.rmSync(tempDir2, { recursive: true, force: true });
     });
   });
+
+  describe('Batch Processing', () => {
+    const createMultipleFiles = (count: number, contentPrefix = 'Content') => {
+      const files: string[] = [];
+      for (let i = 0; i < count; i++) {
+        const fileName = `file${i}.txt`;
+        createFile(fileName, `${contentPrefix} ${i}`);
+        files.push(fileName);
+      }
+      return files;
+    };
+
+    const createFile = (filePath: string, content = '') => {
+      const fullPath = path.join(tempRootDir, filePath);
+      fs.mkdirSync(path.dirname(fullPath), { recursive: true });
+      fs.writeFileSync(fullPath, content);
+    };
+
+    it('should process files in parallel for performance', async () => {
+      // Mock detectFileType to add artificial delay to simulate I/O
+      const detectFileTypeSpy = vi.spyOn(
+        await import('../utils/fileUtils.js'),
+        'detectFileType',
+      );
+
+      // Create files
+      const fileCount = 4;
+      const files = createMultipleFiles(fileCount, 'Batch test');
+
+      // Mock with 100ms delay per file to simulate I/O operations
+      detectFileTypeSpy.mockImplementation(async (_filePath: string) => {
+        await new Promise((resolve) => setTimeout(resolve, 100));
+        return 'text';
+      });
+
+      const startTime = Date.now();
+      const params = { paths: files };
+      const result = await tool.execute(params, new AbortController().signal);
+      const endTime = Date.now();
+
+      const processingTime = endTime - startTime;
+
+      console.log(
+        `Processing time: ${processingTime}ms for ${fileCount} files`,
+      );
+
+      // Verify parallel processing performance improvement
+      // Parallel processing should complete in ~100ms (single file time)
+      // Sequential would take ~400ms (4 files × 100ms each)
+      expect(processingTime).toBeLessThan(200); // Should PASS with parallel implementation
+
+      // Verify all files were processed
+      const content = result.llmContent as string[];
+      expect(content).toHaveLength(fileCount);
+
+      // Cleanup mock
+      detectFileTypeSpy.mockRestore();
+    });
+
+    it('should handle batch processing errors gracefully', async () => {
+      // Create mix of valid and problematic files
+      createFile('valid1.txt', 'Valid content 1');
+      createFile('valid2.txt', 'Valid content 2');
+      createFile('valid3.txt', 'Valid content 3');
+
+      const params = {
+        paths: [
+          'valid1.txt',
+          'valid2.txt',
+          'nonexistent-file.txt', // This will fail
+          'valid3.txt',
+        ],
+      };
+
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+
+      // Should successfully process valid files despite one failure
+      expect(content.length).toBeGreaterThanOrEqual(3);
+      expect(result.returnDisplay).toContain('Successfully read');
+
+      // Verify valid files were processed
+      const expectedPath1 = path.join(tempRootDir, 'valid1.txt');
+      const expectedPath3 = path.join(tempRootDir, 'valid3.txt');
+      expect(content.some((c) => c.includes(expectedPath1))).toBe(true);
+      expect(content.some((c) => c.includes(expectedPath3))).toBe(true);
+    });
+
+    it('should execute file operations concurrently', async () => {
+      // Track execution order to verify concurrency
+      const executionOrder: string[] = [];
+      const detectFileTypeSpy = vi.spyOn(
+        await import('../utils/fileUtils.js'),
+        'detectFileType',
+      );
+
+      const files = ['file1.txt', 'file2.txt', 'file3.txt'];
+      files.forEach((file) => createFile(file, 'test content'));
+
+      // Mock to track concurrent vs sequential execution
+      detectFileTypeSpy.mockImplementation(async (filePath: string) => {
+        const fileName = filePath.split('/').pop() || '';
+        executionOrder.push(`start:${fileName}`);
+
+        // Add delay to make timing differences visible
+        await new Promise((resolve) => setTimeout(resolve, 50));
+
+        executionOrder.push(`end:${fileName}`);
+        return 'text';
+      });
+
+      await tool.execute({ paths: files }, new AbortController().signal);
+
+      console.log('Execution order:', executionOrder);
+
+      // Verify concurrent execution pattern
+      // In parallel execution: all "start:" events should come before all "end:" events
+      // In sequential execution: "start:file1", "end:file1", "start:file2", "end:file2", etc.
+
+      const startEvents = executionOrder.filter((e) =>
+        e.startsWith('start:'),
+      ).length;
+      const firstEndIndex = executionOrder.findIndex((e) =>
+        e.startsWith('end:'),
+      );
+      const startsBeforeFirstEnd = executionOrder
+        .slice(0, firstEndIndex)
+        .filter((e) => e.startsWith('start:')).length;
+
+      // For parallel processing, ALL start events should happen before the first end event
+      expect(startsBeforeFirstEnd).toBe(startEvents); // Should PASS with parallel implementation
+
+      detectFileTypeSpy.mockRestore();
+    });
+  });
 });

packages/core/src/tools/read-many-files.ts

@@ -70,6 +70,27 @@ export interface ReadManyFilesParams {
   };
 }
 
+/**
+ * Result type for file processing operations
+ */
+type FileProcessingResult =
+  | {
+      success: true;
+      filePath: string;
+      relativePathForDisplay: string;
+      fileReadResult: NonNullable<
+        Awaited<ReturnType<typeof processSingleFileContent>>
+      >;
+      reason?: undefined;
+    }
+  | {
+      success: false;
+      filePath: string;
+      relativePathForDisplay: string;
+      fileReadResult?: undefined;
+      reason: string;
+    };
+
 /**
  * Default exclusion patterns for commonly ignored directories and binary file types.
  * These are compatible with glob ignore patterns.
@@ -413,7 +434,9 @@ Use this tool when the user's query implies needing the content of several files
 
     const sortedFiles = Array.from(filesToConsider).sort();
 
-    for (const filePath of sortedFiles) {
+    const fileProcessingPromises = sortedFiles.map(
+      async (filePath): Promise<FileProcessingResult> => {
+        try {
           const relativePathForDisplay = path
             .relative(this.config.getTargetDir(), filePath)
             .replace(/\\/g, '/');
@@ -422,7 +445,10 @@ Use this tool when the user's query implies needing the content of several files
 
           if (fileType === 'image' || fileType === 'pdf') {
             const fileExtension = path.extname(filePath).toLowerCase();
-        const fileNameWithoutExtension = path.basename(filePath, fileExtension);
+            const fileNameWithoutExtension = path.basename(
+              filePath,
+              fileExtension,
+            );
             const requestedExplicitly = inputPatterns.some(
               (pattern: string) =>
                 pattern.toLowerCase().includes(fileExtension) ||
@@ -430,12 +456,13 @@ Use this tool when the user's query implies needing the content of several files
             );
 
             if (!requestedExplicitly) {
-          skippedFiles.push({
-            path: relativePathForDisplay,
+              return {
+                success: false,
+                filePath,
+                relativePathForDisplay,
                 reason:
                   'asset file (image/pdf) was not explicitly requested by name or extension',
-          });
-          continue;
+              };
             }
           }
 
@@ -446,21 +473,66 @@ Use this tool when the user's query implies needing the content of several files
           );
 
           if (fileReadResult.error) {
-        skippedFiles.push({
-          path: relativePathForDisplay,
+            return {
+              success: false,
+              filePath,
+              relativePathForDisplay,
               reason: `Read error: ${fileReadResult.error}`,
+            };
+          }
+
+          return {
+            success: true,
+            filePath,
+            relativePathForDisplay,
+            fileReadResult,
+          };
+        } catch (error) {
+          const relativePathForDisplay = path
+            .relative(this.config.getTargetDir(), filePath)
+            .replace(/\\/g, '/');
+
+          return {
+            success: false,
+            filePath,
+            relativePathForDisplay,
+            reason: `Unexpected error: ${error instanceof Error ? error.message : String(error)}`,
+          };
+        }
+      },
+    );
+
+    const results = await Promise.allSettled(fileProcessingPromises);
+
+    for (const result of results) {
+      if (result.status === 'fulfilled') {
+        const fileResult = result.value;
+
+        if (!fileResult.success) {
+          // Handle skipped files (images/PDFs not requested or read errors)
+          skippedFiles.push({
+            path: fileResult.relativePathForDisplay,
+            reason: fileResult.reason,
           });
         } else {
+          // Handle successfully processed files
+          const { filePath, relativePathForDisplay, fileReadResult } =
+            fileResult;
+
           if (typeof fileReadResult.llmContent === 'string') {
             const separator = DEFAULT_OUTPUT_SEPARATOR_FORMAT.replace(
               '{filePath}',
               filePath,
             );
-          contentParts.push(`${separator}\n\n${fileReadResult.llmContent}\n\n`);
+            contentParts.push(
+              `${separator}\n\n${fileReadResult.llmContent}\n\n`,
+            );
           } else {
             contentParts.push(fileReadResult.llmContent); // This is a Part for image/pdf
           }
+
           processedFilesRelativePaths.push(relativePathForDisplay);
+
           const lines =
             typeof fileReadResult.llmContent === 'string'
               ? fileReadResult.llmContent.split('\n').length
@@ -474,6 +546,13 @@ Use this tool when the user's query implies needing the content of several files
             path.extname(filePath),
           );
         }
+      } else {
+        // Handle Promise rejection (unexpected errors)
+        skippedFiles.push({
+          path: 'unknown',
+          reason: `Unexpected error: ${result.reason}`,
+        });
+      }
     }
 
     let displayMessage = `### ReadManyFiles Result (Target Dir: \`${this.config.getTargetDir()}\`)\n\n`;