Applied patch from Juergen that adds a connection pool to the postgres provider

git-svn-id: http://svn.osgeo.org/qgis/trunk@7268 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: mhugent

src/providers/postgres/qgspostgresprovider.cpp

@@ -97,7 +97,6 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
   else
     mSchemaTableName = "\"" + mTableName + "\"";
 
-
   QgsDebugMsg("Table name is " + mTableName);
   QgsDebugMsg("SQL is " + sqlWhereClause);
   QgsDebugMsg("Connection info is " + mUri.connInfo);
@@ -110,37 +109,18 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
   //pLog.open((const char *)logFile);
   //QgsDebugMsg("Opened log file for " + mTableName);
 
-  PGconn *pd = PQconnectdb((const char *) mUri.connInfo);
-  // check the connection status
-  if (PQstatus(pd) != CONNECTION_OK)
-  {
-    QgsDebugMsg("Connection to database failed");
-    valid = false;
-    return;
-  }
-  
-  // store the connection for future use
-  connection = pd;
-
-  //set client encoding to unicode because QString uses UTF-8 anyway
-  QgsDebugMsg("setting client encoding to UNICODE");
-  
-  int errcode=PQsetClientEncoding(connection, "UNICODE");
-  
-  if(errcode==0) {
-    QgsDebugMsg("encoding successfully set");
-  } else if(errcode==-1) {
-      QgsDebugMsg("error in setting encoding");
-  } else {
-      QgsDebugMsg("undefined return value from encoding setting");
+  connection = connectDb( (const char *)mUri.connInfo );
+  if( connection==NULL ) {
+  	valid = false;
+	return;
   }
 
   QgsDebugMsg("Checking for select permission on the relation\n");
 
   // Check that we can read from the table (i.e., we have
   // select permission).
   QString sql = "select * from " + mSchemaTableName + " limit 1";
-  PGresult* testAccess = PQexec(pd, (const char*)(sql.utf8()));
+  PGresult* testAccess = PQexec(connection, (const char*)(sql.utf8()));
   if (PQresultStatus(testAccess) != PGRES_TUPLES_OK)
   {
     showMessageBox(tr("Unable to access relation"),
@@ -150,33 +130,19 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
         "SQL: " + sql);
     PQclear(testAccess);
     valid = false;
-    PQfinish(connection);
+    disconnectDb();
     return;
   }
   PQclear(testAccess);
 
-  /* Check to see if we have GEOS support and if not, warn the user about
-      the problems they will see :) */
-  QgsDebugMsg("Checking for GEOS support");
-
-  if(!hasGEOS(pd))
-  {
-    showMessageBox(tr("No GEOS Support!"),
-        tr("Your PostGIS installation has no GEOS support.\n"
-    "Feature selection and identification will not "
-    "work properly.\nPlease install PostGIS with " 
-    "GEOS support (http://geos.refractions.net)"));
-  }
-  //--std::cout << "Connection to the database was successful\n";
-
   if (!getGeometryDetails()) // gets srid and geometry type
   {
     // the table is not a geometry table
     numberFeatures = 0;
     valid = false;
 
     QgsDebugMsg("Invalid Postgres layer");
-    PQfinish(connection);
+    disconnectDb();
     return;
   }
 
@@ -187,14 +153,14 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
   // Get the relation oid for use in later queries
   sql = "SELECT oid FROM pg_class WHERE relname = '" + mTableName + "' AND relnamespace = ("
 "SELECT oid FROM pg_namespace WHERE nspname = '" + mSchemaName + "')";
-  PGresult *tresult= PQexec(pd, (const char *)(sql.utf8()));
+  PGresult *tresult= PQexec(connection, (const char *)(sql.utf8()));
   QString tableoid = PQgetvalue(tresult, 0, 0);
   PQclear(tresult);
 
   // Get the table description
   sql = "SELECT description FROM pg_description WHERE "
       "objoid = " + tableoid + " AND objsubid = 0";
-  tresult = PQexec(pd, (const char*) sql.utf8());
+  tresult = PQexec(connection, (const char*) sql.utf8());
   if (PQntuples(tresult) > 0)
     mDataComment = PQgetvalue(tresult, 0, 0);
   PQclear(tresult);
@@ -203,7 +169,7 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
   // field name, type, length, and precision (if numeric)
   sql = "select * from " + mSchemaTableName + " limit 0";
 
-  PGresult *result = PQexec(pd, (const char *) (sql.utf8()));
+  PGresult *result = PQexec(connection, (const char *) (sql.utf8()));
   //--std::cout << "Field: Name, Type, Size, Modifier:" << std::endl;
 
   // The queries inside this loop could possibly be combined into one
@@ -221,20 +187,20 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
         "oid = (SELECT typelem FROM pg_type WHERE "
         "typelem = " + typOid + " AND typlen = -1)";
 
-    PGresult* oidResult = PQexec(pd, (const char *) sql);
+    PGresult* oidResult = PQexec(connection, (const char *) sql);
     QString fieldTypeName = PQgetvalue(oidResult, 0, 0);
     QString fieldSize = PQgetvalue(oidResult, 0, 1);
     PQclear(oidResult);
 
     sql = "SELECT attnum FROM pg_attribute WHERE "
         "attrelid = " + tableoid + " AND attname = '" + fieldName + "'";
-    PGresult *tresult = PQexec(pd, (const char *)(sql.utf8()));
+    PGresult *tresult = PQexec(connection, (const char *)(sql.utf8()));
     QString attnum = PQgetvalue(tresult, 0, 0);
     PQclear(tresult);
 
     sql = "SELECT description FROM pg_description WHERE "
         "objoid = " + tableoid + " AND objsubid = " + attnum;
-    tresult = PQexec(pd, (const char*)(sql.utf8()));
+    tresult = PQexec(connection, (const char*)(sql.utf8()));
     if (PQntuples(tresult) > 0)
       fieldComment = PQgetvalue(tresult, 0, 0);
     PQclear(tresult);
@@ -306,7 +272,7 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
 
   // Close the database connection if the layer isn't going to be loaded.
   if (!valid)
-    PQfinish(connection);
+    disconnectDb();
 }
 
 QgsPostgresProvider::~QgsPostgresProvider()
@@ -329,13 +295,93 @@ QgsPostgresProvider::~QgsPostgresProvider()
   QApplication::sendPostedEvents(this, QGis::ProviderExtentCalcEvent);
   QApplication::sendPostedEvents(this, QGis::ProviderCountCalcEvent);
 #endif
-  PQfinish(connection);
+
+  disconnectDb();
 
   QgsDebugMsg("deconstructing.");
 
   //pLog.flush();
 }
 
+PGconn *QgsPostgresProvider::connectDb(const char *conninfo)
+{
+	if( connections.contains(conninfo) ) 
+	  {
+		QgsDebugMsg(QString("Using cached connection for ") + conninfo);
+		connections[conninfo]->ref++;
+		return connections[conninfo]->conn;
+	  }
+	
+	QgsDebugMsg(QString("New postgres connection for ") + conninfo);
+	
+	PGconn *pd = PQconnectdb(conninfo);
+	// check the connection status
+	if (PQstatus(pd) != CONNECTION_OK) 
+	  {
+	    QgsDebugMsg("Connection to database failed");
+	    return NULL;
+	  }
+
+	//set client encoding to unicode because QString uses UTF-8 anyway
+	QgsDebugMsg("setting client encoding to UNICODE");
+	
+	int errcode=PQsetClientEncoding(pd, "UNICODE");
+	
+	if(errcode==0) 
+	  {
+	    QgsDebugMsg("encoding successfully set");
+	  } 
+	else if(errcode==-1) 
+	  {
+	    QgsDebugMsg("error in setting encoding");
+	  } 
+	else 
+	  {
+	    QgsDebugMsg("undefined return value from encoding setting");
+	  }
+
+	/* Check to see if we have GEOS support and if not, warn the user about
+	   the problems they will see :) */
+	QgsDebugMsg("Checking for GEOS support");
+
+	if(!hasGEOS(pd))
+	  {
+		showMessageBox(tr("No GEOS Support!"),
+				tr("Your PostGIS installation has no GEOS support.\n"
+					"Feature selection and identification will not "
+					"work properly.\nPlease install PostGIS with " 
+					"GEOS support (http://geos.refractions.net)"));
+	  }
+	//--std::cout << "Connection to the database was successful\n";
+	
+	Conn *conn = new Conn(pd);
+	connections.insert( conninfo, conn );
+	
+	return pd;
+}
+
+void QgsPostgresProvider::disconnectDb()
+{
+	QMapIterator <QString, Conn *> i(connections);
+	while( i.hasNext() ) 
+	  {
+		i.next();
+
+		if( i.value()->conn == connection )
+			break;
+	  }
+
+	assert( i.value()->conn==connection );
+	assert( i.value()->ref>0 );
+
+	if( --i.value()->ref==0 ) 
+	  {
+		PQfinish( i.value()->conn );
+		delete (i.value());
+		connections.remove( i.key() );
+	  }
+}
+
 QString QgsPostgresProvider::storageType()
 {
   return "PostgreSQL database with PostGIS extension";
@@ -434,7 +480,6 @@ bool QgsPostgresProvider::getNextFeature(QgsFeature& feature)
     } // if new queue is required
 
     // Now return the next feature from the queue
-    
     feature = mFeatureQueue.front();
     mFeatureQueue.pop();
 
@@ -2609,3 +2654,4 @@ QGISEXTERN bool isProvider(){
   return true;
 }
 
+QMap<QString, QgsPostgresProvider::Conn *> QgsPostgresProvider::connections;

src/providers/postgres/qgspostgresprovider.h

@@ -546,6 +546,18 @@ class QgsPostgresProvider:public QgsVectorDataProvider
      */
     void customEvent ( QCustomEvent * e );
 
+private:
+    struct Conn {
+	Conn(PGconn *connection) : ref(1), conn(connection) {}
+
+	int ref;
+    	PGconn *conn;
+    };
+
+    PGconn *connectDb(const char *conninfo);
+    void disconnectDb();
+
+    static QMap<QString, Conn *> connections;
 };
 
 #endif