From 26f1be106f7ca1d74474f40a3929fc177bd368f5 Mon Sep 17 00:00:00 2001
From: Kai Gritun <kaigritun@gmail.com>
Date: Wed, 11 Feb 2026 23:15:45 -0500
Subject: [PATCH] fix(worker): register leader-now listener early to prevent
 race condition

Fixes #850

The 'leader-now' message from the worker could be lost if the main thread
was still blocked (e.g., awaiting acquireLock) when the message arrived.
This happened because the listener was registered after several async
operations that could yield control.

By moving the listener registration to immediately after the worker
signals it's ready (and before any other async operations), we ensure
the message is never missed, regardless of main thread load.
---
 packages/pglite/src/worker/index.ts | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/packages/pglite/src/worker/index.ts b/packages/pglite/src/worker/index.ts
index 93a552173..9e5b21803 100644
--- a/packages/pglite/src/worker/index.ts
+++ b/packages/pglite/src/worker/index.ts
@@ -148,6 +148,18 @@ export class PGliteWorker
     // Wait for the worker let us know it's ready
     await this.#workerReadyPromise
 
+    // Register leader-now listener early to avoid race condition (#850)
+    // The worker may send 'leader-now' immediately after becoming leader,
+    // before we've finished setting up broadcast channels. By registering
+    // this listener before any async operations, we ensure we don't miss
+    // the message.
+    this.#workerProcess.addEventListener('message', async (event) => {
+      if (event.data.type === 'leader-now') {
+        this.#isLeader = true
+        this.#eventTarget.dispatchEvent(new Event('leader-change'))
+      }
+    })
+
     // Acquire the tab close lock, this is released then the tab, or this
     // PGliteWorker instance, is closed
     const tabCloseLockId = `pglite-tab-close:${this.#tabId}`
@@ -180,13 +192,6 @@ export class PGliteWorker
       }
     })
 
-    this.#workerProcess.addEventListener('message', async (event) => {
-      if (event.data.type === 'leader-now') {
-        this.#isLeader = true
-        this.#eventTarget.dispatchEvent(new Event('leader-change'))
-      }
-    })
-
     this.#leaderNotifyLoop()
 
     // Init array types