handle multiple waiters for the same module

src/browser/ScriptManager.zig

@@ -326,15 +326,28 @@ pub fn waitForModule(self: *ScriptManager, url: [:0]const u8) !GetResult {
     };
     const sync = entry.value_ptr.*;
 
+    // We can have multiple scripts waiting for the same module in concurrency.
+    // We use the waiters to ensures only the last waiter deinit the resources.
+    sync.waiters += 1;
+    defer sync.waiters -= 1;
+
     var client = self.client;
     while (true) {
         switch (sync.state) {
             .loading => {},
             .done => {
-                // Our caller has its own higher level cache (caching the
-                // actual compiled module). There's no reason for us to keep this
-                defer self.sync_module_pool.destroy(sync);
-                defer self.sync_modules.removeByPtr(entry.key_ptr);
+                if (sync.waiters == 1) {
+                    // Our caller has its own higher level cache (caching the
+                    // actual compiled module). There's no reason for us to keep
+                    // this if we are the last waiter.
+                    defer self.sync_module_pool.destroy(sync);
+                    defer self.sync_modules.removeByPtr(entry.key_ptr);
+                    return .{
+                        .buffer = sync.buffer,
+                        .buffer_pool = &self.buffer_pool,
+                    };
+                }
+
                 return .{
                     .buffer = sync.buffer,
                     .buffer_pool = &self.buffer_pool,
@@ -882,6 +895,8 @@ const SyncModule = struct {
     manager: *ScriptManager,
     buffer: std.ArrayListUnmanaged(u8) = .{},
     state: State = .loading,
+    // number of waiters for the module.
+    waiters: u8 = 0,
 
     const State = union(enum) {
         done,