QSerialPort emits error in destructor

QSerialPort::~QSerialPort() helpfully calls QSerialPort::close() to ensure the serial port is not in use anymore. close() in turn emits an error [1] if it is called when it's already closed. This results in an error every time a QSerialPort is destroyed which has never been open()'ed or has already been close()'d manually.

This wouldn't be much of a problem as the object is destroyed anyway, but it does emit a signal in the process. This signal can be inconvenient as it is emitted during a destructor call: If a class Foo has a QSerialPort instance as a member and has a slot connected to the QSerialPort::SerialPortError signal, the slot is called after the Foo's destructor. This can cause some mayhem as Foo is already destroyed.

See attached code for an example.

I propose a simple fix for the solution: don't call close() in the destructor if the port is already closed.

E.g. in [2], instead of

QSerialPort::~QSerialPort()

{ close(); delete d_ptr; }

use this

QSerialPort::~QSerialPort()

{ if (this->isOpen()) close(); delete d_ptr; }

To summarize:

1. an object Foo derived from QObject and having an instance of QSerialPort is destroyed
2. Foo::~Foo() is called, Foo gets destroyed
3. QSerialPort::~QSerialPort() is called and calls QSerialPort::close()
4. QSerialPort::close() emits an error signal because it is already closed
5. The problem: This signal may now call Foo::someslot() even tough Foo was already destroyed in step 2
6. all members of Foo are destroyed, now it's ancestors are destroyed: QObject::~QObject() is called and disconnects all its signals and slots

Normally, a signal will never call a slot of a destroyed object as QObject::~QObject() will disconnect a destroyed object, but the destructor of a parent class is called after the destructor of the members of the class.

[1] https://qt.gitorious.org/qt/qtserialport/source/04a3308346190a70509a759423993f6bcc365328:src/serialport/qserialport.cpp#L564-1371

[2] https://qt.gitorious.org/qt/qtserialport/source/04a3308346190a70509a759423993f6bcc365328:src/serialport/qserialport.cpp#L425-1371