[wasm] Defer parsing of wasm stack symbolication maps (#99974)

Right now if a wasm app's assets list contains symbol maps for stack symbolication, we parse them at startup. This allocates a lot of garbage and is generally slow, and during normal execution the symbol map(s) may never actually be used, so this PR defers the actual parsing until first use.

Author: kg

src/mono/browser/runtime/logging.ts

@@ -2,7 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 /* eslint-disable no-console */
-import { INTERNAL, runtimeHelpers } from "./globals";
+import { INTERNAL, runtimeHelpers, mono_assert } from "./globals";
 import { utf8ToString } from "./strings";
 import { CharPtr, VoidPtr } from "./types/emscripten";
 
@@ -35,6 +35,7 @@ export function mono_log_error(msg: string, ...data: any) {
 }
 
 export const wasm_func_map = new Map<number, string>();
+let wasm_pending_symbol_table : string | undefined;
 const regexes: any[] = [];
 
 // V8
@@ -54,6 +55,8 @@ regexes.push(/(?<replaceSection><[^ >]+>[.:]wasm-function\[(?<funcNum>[0-9]+)\])
 
 export function mono_wasm_symbolicate_string(message: string): string {
     try {
+        performDeferredSymbolMapParsing();
+
         if (wasm_func_map.size == 0)
             return message;
 
@@ -143,22 +146,40 @@ export function mono_wasm_trace_logger(log_domain_ptr: CharPtr, log_level_ptr: C
 
 
 export function parseSymbolMapFile(text: string) {
-    text.split(/[\r\n]/).forEach((line: string) => {
-        const parts: string[] = line.split(/:/);
-        if (parts.length < 2)
-            return;
+    // Symbol map parsing is very expensive, so doing it during startup is wasteful
+    //  instead, we defer it until the first time the symbol map is needed - which
+    //  may be never
+    mono_assert(!wasm_pending_symbol_table, "Another symbol map was already loaded");
+    wasm_pending_symbol_table = text;
+    mono_log_debug(`Deferred loading of ${text.length}ch symbol map`);
+}
 
-        parts[1] = parts.splice(1).join(":");
-        wasm_func_map.set(Number(parts[0]), parts[1]);
-    });
+function performDeferredSymbolMapParsing() {
+    if (!wasm_pending_symbol_table)
+        return;
 
-    mono_log_debug(`Loaded ${wasm_func_map.size} symbols`);
+    const text = wasm_pending_symbol_table!;
+    wasm_pending_symbol_table = undefined;
+    try {
+        text.split(/[\r\n]/).forEach((line: string) => {
+            const parts: string[] = line.split(/:/);
+            if (parts.length < 2)
+                return;
+
+            parts[1] = parts.splice(1).join(":");
+            wasm_func_map.set(Number(parts[0]), parts[1]);
+        });
+        mono_log_debug(`Loaded ${wasm_func_map.size} symbols`);
+    } catch (exc) {
+        mono_log_warn(`Failed to load symbol map: ${exc}`);
+    }
 }
 
 export function mono_wasm_get_func_id_to_name_mappings() {
+    performDeferredSymbolMapParsing();
     return [...wasm_func_map.values()];
 }
 
 export function mono_wasm_console_clear() {
     console.clear();
-}
+}