Reuse Printers in symbolToStringWorker

Author: jakebailey

src/compiler/checker.ts

@@ -871,6 +871,7 @@ import {
     pathIsRelative,
     PatternAmbientModule,
     PlusToken,
+    pooled,
     PostfixUnaryExpression,
     PrefixUnaryExpression,
     PrivateIdentifier,
@@ -2173,6 +2174,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         [".json", ".json"],
     ];
 
+    const symbolToStringWorkerSourceFilePrinter = pooled(() => createPrinter({ removeComments: true, neverAsciiEscape: true }), (printer) => printer.reset());
+    const symbolToStringWorkerNonSourceFilePrinter = pooled(() => createPrinter({ removeComments: true }), (printer) => printer.reset());
+
     initializeTypeChecker();
 
     return checker;
@@ -6123,9 +6127,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         function symbolToStringWorker(writer: EmitTextWriter) {
             const entity = builder(symbol, meaning!, enclosingDeclaration, nodeFlags)!; // TODO: GH#18217
             // add neverAsciiEscape for GH#39027
-            const printer = enclosingDeclaration?.kind === SyntaxKind.SourceFile ? createPrinter({ removeComments: true, neverAsciiEscape: true }) : createPrinter({ removeComments: true });
+            const [printer, disposePrinter] = enclosingDeclaration?.kind === SyntaxKind.SourceFile
+                ? symbolToStringWorkerSourceFilePrinter()
+                : symbolToStringWorkerNonSourceFilePrinter();
             const sourceFile = enclosingDeclaration && getSourceFileOfNode(enclosingDeclaration);
             printer.writeNode(EmitHint.Unspecified, entity, /*sourceFile*/ sourceFile, writer);
+            disposePrinter();
             return writer;
         }
     }

src/compiler/core.ts

@@ -2917,3 +2917,33 @@ export function isNodeLikeSystem(): boolean {
         && !process.browser
         && typeof module === "object";
 }
+
+/** @internal */
+export function pooled<T>(fn: () => T, reset: (value: T) => void): () => [value: T, dispose: () => void] {
+    // TODO(jakebailey): this is supposed to be something like Go's sync.Pool,
+    // but I don't know of a way to "eventually" return the pool's contents to GC.
+    // For now, this just holds onto the objects even when they may not have been
+    // in use for a long time.
+    const pool: T[] = [];
+
+    return () => {
+        let value: T;
+        if (pool.length > 1) {
+            const end = pool.length - 1;
+            value = pool[end];
+            pool.length = end;
+        }
+        else {
+            value = fn();
+        }
+
+        const dispose = () => {
+            if (pool.length < 8) {
+                reset(value);
+                pool.push(value);
+            }
+        };
+
+        return [value, dispose];
+    };
+}

src/compiler/emitter.ts

@@ -1428,7 +1428,8 @@ export function createPrinter(printerOptions: PrinterOptions = {}, handlers: Pri
         writeList,
         writeFile,
         writeBundle,
-        bundleFileInfo
+        bundleFileInfo,
+        reset,
     };
 
     function printNode(hint: EmitHint, node: Node, sourceFile: SourceFile): string {

src/compiler/types.ts

@@ -9165,6 +9165,7 @@ export interface Printer {
     /** @internal */ writeFile(sourceFile: SourceFile, writer: EmitTextWriter, sourceMapGenerator: SourceMapGenerator | undefined): void;
     /** @internal */ writeBundle(bundle: Bundle, writer: EmitTextWriter, sourceMapGenerator: SourceMapGenerator | undefined): void;
     /** @deprecated @internal */ bundleFileInfo?: BundleFileInfo;
+    /** @internal */ reset(): void;
 }
 
 /** @deprecated @internal */