From b91616e2f1abd16b4cd9ce7de44b75aa3a2a9b7e Mon Sep 17 00:00:00 2001
From: PA Dev Bot <344001113+pa-devbot@users.noreply.github.com>
Date: Sat, 31 Oct 2026 11:25:02 +0000
Subject: [PATCH] Thread pool: spawn threads in dispatch()

dispatch() enqueued the task and called notify_one(), but never called
spawn_threads(). Since all of the global pools start with zero threads,
a plain dispatch() on a cold pool woke no one and the task never ran.
On a pool with fewer threads than its maximum, the pool also never
grew to use the headroom.

dispatch_now_blocking(), try_dispatch_now() and run_in_parallel() all
call spawn_threads(), so only the plain dispatch() path was affected.

Call spawn_threads() after the task is enqueued, the same as the other
entry points.
---
 Common/Cpp/Concurrency/Backends/ThreadPool_Default.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Common/Cpp/Concurrency/Backends/ThreadPool_Default.cpp b/Common/Cpp/Concurrency/Backends/ThreadPool_Default.cpp
index acf1edea93..297ba275cb 100644
--- a/Common/Cpp/Concurrency/Backends/ThreadPool_Default.cpp
+++ b/Common/Cpp/Concurrency/Backends/ThreadPool_Default.cpp
@@ -99,6 +99,13 @@ AsyncTask ThreadPool_Default::dispatch(std::function<void()>&& func){
             task = AsyncTask(std::make_unique<AsyncTask_Cpp>(std::move(func)));
             ptr = task.core();
             ptr->report_started();
+
+            //  Spawn threads to pick up the work. Without this, a pool that
+            //  has not reached its maximum thread count (or has no threads
+            //  at all, as the global pools start out) would never grow, and
+            //  with no threads the notify_one() below would wake nothing and
+            //  the task would never run.
+            spawn_threads();
         }catch (...){
             m_queue.pop_back();
             throw;