Ensure QModbusDevice::close() handles being unconnected alreadyv5.11.0-beta2

Prior to this change, an unconnected device would transition into the Closing
state if disconnectDevice() was called. Since the transition to Unconnected is
bound to sockets being closed the already unconnected ModbusDevice would
forever hang in CLosing.

Task-number: QTBUG-66648
Change-Id: Ia439f6b63b7d4ab7f377a45fb09cb5f5b99627f7
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Karsten Heimrich <karsten.heimrich@qt.io>

2 files changed, 13 insertions, 0 deletions

diff --git a/src/serialbus/qmodbusdevice.cpp b/src/serialbus/qmodbusdevice.cpp
index 4aaae87..7ef358c 100644
--- a/src/serialbus/qmodbusdevice.cpp
+++ b/src/serialbus/qmodbusdevice.cpp
@@ -258,6 +258,9 @@ bool QModbusDevice::connectDevice()
 */
 void QModbusDevice::disconnectDevice()
 {
+    if (state() == QModbusDevice::UnconnectedState)
+        return;
+
     setState(QModbusDevice::ClosingState);
 
     //Unconnected is set by backend -> might be delayed by event loop
diff --git a/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp b/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp
index 836d881..748c4bf 100644
--- a/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp
+++ b/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp
@@ -64,6 +64,7 @@ private slots:
     void cleanupTestCase();
 
     void connectDevice();
+    void disconnectDevice();
     void state();
     void error();
 
@@ -98,6 +99,15 @@ void tst_QModbusDevice::connectDevice()
     QVERIFY(!device->connectDevice());
 }
 
+void tst_QModbusDevice::disconnectDevice()
+{
+    //see QTBUG-66648
+    DummyDevice dev;
+    QCOMPARE(dev.state(), QModbusDevice::UnconnectedState);
+    dev.disconnectDevice();
+    QCOMPARE(dev.state(), QModbusDevice::UnconnectedState);
+}
+
 void tst_QModbusDevice::state()
 {
     device->setState(QModbusDevice::ConnectedState);