From a2010f17b88ee72940f4c0955a67c3cee8a2e4f9 Mon Sep 17 00:00:00 2001
From: John Sully <john@csquare.ca>
Date: Mon, 31 May 2021 01:14:11 +0000
Subject: [PATCH 1/2] Fix deadlock in async work queue

Former-commit-id: 3265f2908e8d3aa567b3b9e6b141a7881c795053
---
 src/AsyncWorkQueue.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/AsyncWorkQueue.cpp b/src/AsyncWorkQueue.cpp
index dae36cc06..9544d1a00 100644
--- a/src/AsyncWorkQueue.cpp
+++ b/src/AsyncWorkQueue.cpp
@@ -25,7 +25,8 @@ void AsyncWorkQueue::WorkerThreadMain()
     while (!m_fQuitting)
     {
         std::unique_lock<std::mutex> lock(m_mutex);
-        m_cvWakeup.wait(lock);
+        if (m_workqueue.empty())
+            m_cvWakeup.wait(lock);
 
         while (!m_workqueue.empty())
         {

From ac49c7158c6399d73b67a364b99514b6f9a56cbd Mon Sep 17 00:00:00 2001
From: John Sully <john@csquare.ca>
Date: Mon, 31 May 2021 01:14:28 +0000
Subject: [PATCH 2/2] Eliminate unnecessary global locks

Former-commit-id: 8f924ed0979f3cf7cd290395d1b1eec358979325
---
 src/AsyncWorkQueue.cpp | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/AsyncWorkQueue.cpp b/src/AsyncWorkQueue.cpp
index 9544d1a00..fe02e5212 100644
--- a/src/AsyncWorkQueue.cpp
+++ b/src/AsyncWorkQueue.cpp
@@ -18,9 +18,9 @@ void AsyncWorkQueue::WorkerThreadMain()
 
     vars.clients_pending_asyncwrite = listCreate();
 
-    aeAcquireLock();
+    m_mutex.lock();
     m_vecpthreadVars.push_back(&vars);
-    aeReleaseLock();
+    m_mutex.unlock();
 
     while (!m_fQuitting)
     {
@@ -42,9 +42,11 @@ void AsyncWorkQueue::WorkerThreadMain()
 
         lock.unlock();
         serverTL->gcEpoch = g_pserver->garbageCollector.startEpoch();
-        aeAcquireLock();
-        ProcessPendingAsyncWrites();
-        aeReleaseLock();
+        if (listLength(serverTL->clients_pending_asyncwrite)) {
+            aeAcquireLock();
+            ProcessPendingAsyncWrites();
+            aeReleaseLock();
+        }
         g_pserver->garbageCollector.endEpoch(serverTL->gcEpoch);
         serverTL->gcEpoch.reset();
     }
@@ -61,6 +63,7 @@ bool AsyncWorkQueue::removeClientAsyncWrites(client *c)
 {
     bool fFound = false;
     aeAcquireLock();
+    m_mutex.lock();
     for (auto pvars : m_vecpthreadVars)
     {
         listIter li;
@@ -75,6 +78,7 @@ bool AsyncWorkQueue::removeClientAsyncWrites(client *c)
             }
         }
     }
+    m_mutex.unlock();
     aeReleaseLock();
     return fFound;
 }