From 0cba0ed30be1c0f70abd5c6ba958d1b869280164 Mon Sep 17 00:00:00 2001
From: Malavan Sotheeswaran <msotheeswaran@snapchat.com>
Date: Thu, 9 Feb 2023 12:06:27 -0800
Subject: [PATCH] refactor aeReleaseForkLockChild to capture releaseRead case

---
 src/ae.cpp          |  4 ++--
 src/ae.h            |  2 +-
 src/readwritelock.h | 21 +++++++--------------
 src/server.cpp      |  3 ++-
 4 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/src/ae.cpp b/src/ae.cpp
index af4bd1369..99093daa8 100644
--- a/src/ae.cpp
+++ b/src/ae.cpp
@@ -859,9 +859,9 @@ void aeReleaseForkLock()
     g_forkLock.downgradeWrite();
 }
 
-void aeReleaseForkLockChild()
+void aeForkLockInChild()
 {
-    g_forkLock.downgradeWriteChild();
+    g_forkLock.setNotify(false);
 }
 
 int aeThreadOwnsLock()
diff --git a/src/ae.h b/src/ae.h
index 384aaaa2b..3868db4a0 100644
--- a/src/ae.h
+++ b/src/ae.h
@@ -171,7 +171,7 @@ int aeTryAcquireLock(int fWeak);
 void aeThreadOffline();
 void aeReleaseLock();
 void aeReleaseForkLock();
-void aeReleaseForkLockChild();
+void aeForkLockInChild();
 int aeThreadOwnsLock();
 void aeSetThreadOwnsLockOverride(int fOverride);
 int aeLockContested(int threshold);
diff --git a/src/readwritelock.h b/src/readwritelock.h
index 4cc839991..79f0ac710 100644
--- a/src/readwritelock.h
+++ b/src/readwritelock.h
@@ -8,6 +8,7 @@ class readWriteLock {
     int m_readCount = 0;
     int m_writeCount = 0;
     bool m_writeWaiting = false;
+    bool m_notify = true;
 public:
     readWriteLock(const char *name) : m_readLock(name), m_writeLock(name) {}
 
@@ -65,7 +66,8 @@ public:
     void releaseRead() {
         std::unique_lock<fastlock> rm(m_readLock);
         m_readCount--;
-        m_cv.notify_all();
+        if (m_notify)
+            m_cv.notify_all();
     }
 
     void releaseWrite(bool exclusive = true) {
@@ -74,16 +76,8 @@ public:
         if (exclusive)
             m_writeLock.unlock();
         m_writeCount--;
-        m_cv.notify_all();
-    }
-
-    void releaseWriteChild(bool exclusive = true) {
-        std::unique_lock<fastlock> rm(m_readLock);
-        serverAssert(m_writeCount > 0);
-        if (exclusive)
-            m_writeLock.unlock();
-        m_writeCount--;
-        m_writeWaiting = false;
+        if (m_notify)
+            m_cv.notify_all();
     }
 
     void downgradeWrite(bool exclusive = true) {
@@ -91,9 +85,8 @@ public:
         acquireRead();
     }
 
-    void downgradeWriteChild(bool exclusive = true) {
-        releaseWriteChild(exclusive);
-        acquireRead();
+    void setNotify(bool notify) {
+        m_notify = notify;
     }
 
     bool hasReader() {
diff --git a/src/server.cpp b/src/server.cpp
index d3e641d18..9b983585e 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -6888,7 +6888,8 @@ int redisFork(int purpose) {
     latencyAddSampleIfNeeded("fork-lock",(ustime()-startWriteLock)/1000);
     if ((childpid = fork()) == 0) {
         /* Child */
-        aeReleaseForkLockChild();
+        aeForkLockInChild();
+        aeReleaseForkLock();
         g_pserver->in_fork_child = purpose;
         setOOMScoreAdj(CONFIG_OOM_BGCHILD);
         setupChildSignalHandlers();