Use Promise internal for handling run dependencies. NFC

This is a logical followup to #27121, and comes with a codesize
saving in many cases.

Add `$resolveRunDependencies` to allow awaiting the resolution of all
active run dependencies. This is useful for async runtime operations
like `emscripten_async_load_script` which need to wait for loaded
scripts to finish their own async setup (e.g. file preloading) before
triggering their onload callbacks.

Codesize impact:
- test_codesize_file_preload: -19 bytes (JS)
- test_codesize_hello_dylink_all: +40 bytes (JS)
- All other tests (including C++ tests): 0 bytes change (fully DCE'd)

Author: sbc100

src/lib/libbrowser.js

@@ -617,7 +617,7 @@ var LibraryBrowser = {
   },
 
   // TODO: currently not callable from a pthread, but immediately calls onerror() if not on main thread.
-  emscripten_async_load_script__deps: ['$UTF8ToString', '$runDependencies', '$dependenciesFulfilled'],
+  emscripten_async_load_script__deps: ['$UTF8ToString', '$runDependencies', '$resolveRunDependencies'],
   emscripten_async_load_script: async (url, onload, onerror) => {
     url = UTF8ToString(url);
 #if PTHREADS
@@ -635,12 +635,7 @@ var LibraryBrowser = {
     var loadDone = () => {
       {{{ runtimeKeepalivePop() }}}
       if (onload) {
-        var onloadCallback = () => callUserCallback({{{ makeDynCall('v', 'onload') }}});
-        if (runDependencies > 0) {
-          dependenciesFulfilled = onloadCallback;
-        } else {
-          onloadCallback();
-        }
+        resolveRunDependencies().then(() => callUserCallback({{{ makeDynCall('v', 'onload') }}}));
       }
     }
 

src/lib/libcore.js

@@ -2268,24 +2268,32 @@ addToLibrary({
   // it happens right before run - run will be postponed until
   // the dependencies are met.
   $runDependencies__internal: true,
+  $runDependencies__deps: ['$resolveRunDependencies'],
   $runDependencies: 0,
-  // overridden to take different actions when all run dependencies are fulfilled
-  $dependenciesFulfilled__internal: true,
-  $dependenciesFulfilled: null,
+  $dependenciesPromise__internal: true,
+  $dependenciesPromise: null,
+  $resolveRunDependencies__internal: true,
+  $resolveRunDependencies__deps: ['$dependenciesPromise'],
+  $resolveRunDependencies: async () => dependenciesPromise,
 #if ASSERTIONS
   $runDependencyTracking__internal: true,
   $runDependencyTracking: {},
   $runDependencyWatcher__internal: true,
   $runDependencyWatcher: null,
 #endif
 
-  $addRunDependency__deps: ['$runDependencies', '$removeRunDependency',
+  $addRunDependency__deps: ['$runDependencies', '$removeRunDependency', '$dependenciesPromise',
 #if ASSERTIONS
     '$runDependencyTracking',
     '$runDependencyWatcher',
 #endif
   ],
   $addRunDependency: (id) => {
+    if (!runDependencies) {
+      var resolve;
+      dependenciesPromise = new Promise((r) => resolve = r);
+      dependenciesPromise.resolve = resolve;
+    }
     runDependencies++;
 
 #if expectToReceiveOnModule('monitorRunDependencies')
@@ -2328,7 +2336,7 @@ addToLibrary({
 #endif
   },
 
-  $removeRunDependency__deps: ['$runDependencies', '$dependenciesFulfilled',
+  $removeRunDependency__deps: ['$runDependencies', '$dependenciesPromise',
 #if ASSERTIONS
     '$runDependencyTracking',
     '$runDependencyWatcher',
@@ -2349,18 +2357,14 @@ addToLibrary({
     assert(runDependencyTracking[id]);
     delete runDependencyTracking[id];
 #endif
-    if (runDependencies == 0) {
+    if (!runDependencies) {
 #if ASSERTIONS
       if (runDependencyWatcher !== null) {
         clearInterval(runDependencyWatcher);
         runDependencyWatcher = null;
       }
 #endif
-      if (dependenciesFulfilled) {
-        var callback = dependenciesFulfilled;
-        dependenciesFulfilled = null;
-        callback(); // can add another dependenciesFulfilled
-      }
+      dependenciesPromise.resolve();
     }
   },
 #endif

src/postamble.js

@@ -134,11 +134,11 @@ function stackCheckInit() {
   preRun();
 
 #if '$runDependencies' in addedLibraryItems
-  if (runDependencies > 0) {
+  if (runDependencies) {
 #if RUNTIME_DEBUG
     dbg('run: waiting on runDependencies');
 #endif
-    await new Promise((resolve) => dependenciesFulfilled = resolve);
+    await resolveRunDependencies();
   }
 #endif
 

test/codesize/test_codesize_file_preload.expected.js

@@ -1305,22 +1305,25 @@ var FS_createDataFile = (...args) => FS.createDataFile(...args);
 
 var getUniqueRunDependency = id => id;
 
-var runDependencies = 0;
+var dependenciesPromise = null;
+
+var resolveRunDependencies = async () => dependenciesPromise;
 
-var dependenciesFulfilled = null;
+var runDependencies = 0;
 
 var removeRunDependency = id => {
   runDependencies--;
-  if (runDependencies == 0) {
-    if (dependenciesFulfilled) {
-      var callback = dependenciesFulfilled;
-      dependenciesFulfilled = null;
-      callback();
-    }
+  if (!runDependencies) {
+    dependenciesPromise.resolve();
   }
 };
 
 var addRunDependency = id => {
+  if (!runDependencies) {
+    var resolve;
+    dependenciesPromise = new Promise(r => resolve = r);
+    dependenciesPromise.resolve = resolve;
+  }
   runDependencies++;
 };
 
@@ -3180,8 +3183,8 @@ function callMain() {
 
 async function run() {
   preRun();
-  if (runDependencies > 0) {
-    await new Promise(resolve => dependenciesFulfilled = resolve);
+  if (runDependencies) {
+    await resolveRunDependencies();
   }
   if (ABORT) return;
   initRuntime();

test/codesize/test_codesize_file_preload.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 22157,
-  "a.out.js.gz": 9192,
+  "a.out.js": 22138,
+  "a.out.js.gz": 9190,
   "a.out.nodebug.wasm": 1666,
   "a.out.nodebug.wasm.gz": 945,
-  "total": 23823,
-  "total_gz": 10137,
+  "total": 23804,
+  "total_gz": 10135,
   "sent": [
     "a (fd_write)"
   ],

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
-  "a.out.js": 268405,
-  "a.out.nodebug.wasm": 587745,
-  "total": 856150,
+  "a.out.js": 268450,
+  "a.out.nodebug.wasm": 587575,
+  "total": 856025,
   "sent": [
     "IMG_Init",
     "IMG_Load",
@@ -256,8 +256,6 @@
     "__syscall_rmdir",
     "__syscall_sendmsg",
     "__syscall_sendto",
-    "__syscall_setsockopt",
-    "__syscall_shutdown",
     "__syscall_socket",
     "__syscall_stat64",
     "__syscall_statfs64",
@@ -1777,8 +1775,6 @@
     "env.__syscall_rmdir",
     "env.__syscall_sendmsg",
     "env.__syscall_sendto",
-    "env.__syscall_setsockopt",
-    "env.__syscall_shutdown",
     "env.__syscall_socket",
     "env.__syscall_stat64",
     "env.__syscall_statfs64",
@@ -2231,6 +2227,8 @@
     "__syscall_setpgid",
     "__syscall_setpriority",
     "__syscall_setsid",
+    "__syscall_setsockopt",
+    "__syscall_shutdown",
     "__syscall_socketpair",
     "__syscall_sync",
     "__syscall_uname",
@@ -4098,7 +4096,8 @@
     "$__syscall_setdomainname",
     "$__syscall_setpgid",
     "$__syscall_setpriority",
-    "$__syscall_socketpair",
+    "$__syscall_setsockopt",
+    "$__syscall_shutdown",
     "$__syscall_sync",
     "$__syscall_uname",
     "$__syscall_wait4",
@@ -5090,7 +5089,6 @@
     "$shm_open",
     "$shm_unlink",
     "$shr",
-    "$shutdown",
     "$sift",
     "$sigaddset",
     "$sigaltstack",