refactor aeReleaseForkLockChild to capture releaseRead case

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()

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);

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) {}
 
@@ -65,6 +66,7 @@ public:
     void releaseRead() {
         std::unique_lock<fastlock> rm(m_readLock);
         m_readCount--;
+        if (m_notify)
             m_cv.notify_all();
     }
 
@@ -74,26 +76,17 @@ public:
         if (exclusive)
             m_writeLock.unlock();
         m_writeCount--;
+        if (m_notify)
             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;
-    }
-
     void downgradeWrite(bool exclusive = true) {
         releaseWrite(exclusive);
         acquireRead();
     }
 
-    void downgradeWriteChild(bool exclusive = true) {
+    void setNotify(bool notify) {
-        releaseWriteChild(exclusive);
+        m_notify = notify;
-        acquireRead();
     }
 
     bool hasReader() {

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();