Ticket #7836: PurgeIdleConnections_fix.patch

libs/libmythdb/mythdbcon.h

@@ -56 +56 @@
     QList<MSqlDatabase*> m_pool;
     QMutex m_lock;
     QSemaphore *m_sem;
-    int m_connID;
+    int m_nextConnID;
+    int m_connCount;
 
     MSqlDatabase *m_schedCon;
     MSqlDatabase *m_DDCon;

libs/libmythdb/mythdbcon.cpp

@@ -185 +185 @@
 
 MDBManager::MDBManager()
 {
-    m_connID = 0;
+    m_nextConnID = 0;
+    m_connCount = 0;
 
     m_sem = new QSemaphore(20);
 
@@ -216 +217 @@
 
     if (m_pool.isEmpty())
     {
-        db = new MSqlDatabase("DBManager" + QString::number(m_connID++));
-        VERBOSE(VB_IMPORTANT, QString("New DB connection, total: %1").arg(m_connID));
+        db = new MSqlDatabase("DBManager" + QString::number(m_nextConnID++));
+        ++m_connCount;
+        VERBOSE(VB_IMPORTANT, QString("New DB connection, total: %1").arg(m_connCount));
     }
     else
         db = m_pool.takeLast();
@@ -242 +244 @@
     m_lock.unlock();
     m_sem->release();
 
-    PurgeIdleConnections();
+    // Delay purging of idle connections as long as possible.
+    //PurgeIdleConnections();
 }
 
 void MDBManager::PurgeIdleConnections(void)
@@ -252 +255 @@
     QDateTime now = QDateTime::currentDateTime();
     QList<MSqlDatabase*>::iterator it = m_pool.begin();
 
+    unsigned purgedConnections=0, totalConnections=0;
+    MSqlDatabase *newDb = NULL;
     while (it != m_pool.end())
     {
+        totalConnections ++;
         if ((*it)->m_lastDBKick.secsTo(now) <= 3600)
         {
             ++it;
@@ -264 +270 @@
         // not been used in the past hour.
         MSqlDatabase *entry = *it;
         it = m_pool.erase(it);
-        --m_connID;
+        --m_connCount;
+        purgedConnections ++;
+        // Qt's MySQL driver apparently keeps track of the number of
+        // open DB connections, and when it hits 0, calls
+        // my_thread_global_end().  The mysql library then assumes the
+        // application is ending and that all threads that created DB
+        // connections have already exited.  This is rarely true, and
+        // may result in the mysql library pausing 5 seconds and
+        // printing a message like "Error in my_thread_global_end(): 1
+        // threads didn't exit".  This workaround simply creates an
+        // extra DB connection before all pooled connections are
+        // purged so that my_thread_global_end() won't be called.
+        if (it == m_pool.end() &&
+            purgedConnections > 0 &&
+            totalConnections == purgedConnections)
+        {
+            newDb = new MSqlDatabase("DBManager" +
+                                     QString::number(m_nextConnID++));
+            ++m_connCount;
+            VERBOSE(VB_IMPORTANT,
+                    QString("New DB connection, total: %1").arg(m_connCount));
+            newDb->m_lastDBKick = QDateTime::currentDateTime();
+        }
+        VERBOSE(VB_IMPORTANT, "Deleting idle DB connection...");
         delete entry;
+        VERBOSE(VB_IMPORTANT, "Done deleting idle DB connection.");
     }
+    if (newDb != NULL)
+    {
+        m_pool.prepend(newDb);
+    }
+    if (purgedConnections > 0)
+    {
+        VERBOSE(VB_IMPORTANT,
+                QString("Purged %1 idle of %2 total DB connections.")
+                .arg(purgedConnections).arg(totalConnections));
+    }
 }
 
 MSqlDatabase *MDBManager::getSchedCon()