QCA::SyncThread Class Reference
[QCA user API]

Convenience class to run a thread and interact with it synchronously. More...

#include <QtCrypto>

Inheritance diagram for QCA::SyncThread:

QThread
Collaboration diagram for QCA::SyncThread:

Collaboration graph
[legend]

List of all members.

Public Member Functions

QVariant call (QObject *obj, const QByteArray &method, const QVariantList &args=QVariantList(), bool *ok=0)
void start ()
void stop ()
 SyncThread (QObject *parent=0)
 ~SyncThread ()

Protected Member Functions

virtual void atEnd ()=0
virtual void atStart ()=0
virtual void run ()

Friends

class Private

Related Functions

(Note that these are not member functions.)

QCA_EXPORT bool invokeMethodWithVariants (QObject *obj, const QByteArray &method, const QVariantList &args, QVariant *ret, Qt::ConnectionType type=Qt::AutoConnection)
QCA_EXPORT QByteArray methodReturnType (const QMetaObject *obj, const QByteArray &method, const QList< QByteArray > argTypes)


Detailed Description

Convenience class to run a thread and interact with it synchronously.

SyncThread makes it easy to perform the common practice of starting a thread, running some objects in that thread, and then interacting with those objects safely. Often, there is no need to directly use threading primitives (e.g. QMutex), resulting in very clean multi-threaded code.

Note:
The following is an excerpt from http://delta.affinix.com/2006/11/13/synchronized-threads-part-3/
---
With SyncThread, you can start, stop, and call a method in another thread while the main thread sleeps. The only requirement is that the methods be declared as slots.

Below is a contrived example, where we have an object in another thread that increments a counter over a some interval, using the Qt event loop, and provides a method to inspect the value.

First, the Counter object:

class Counter : public QObject
{
        Q_OBJECT
private:
        int x;
        QTimer timer;

public:
        Counter() : timer(this)
        {
                x = 0;
                connect(&timer, SIGNAL(timeout()), SLOT(t_timeout()));
        }

public slots:
        void start(int seconds)
        {
                timer.setInterval(seconds * 1000);
                timer.start();
        }

        int value() const
        {
                return x;
        }

private slots:
        void t_timeout()
        {
                ++x;
        }
};

Looks like a typical object, no surprises.

Now to wrap Counter with SyncThread. We went over how to do this in the first article, and it is very straightforward:

class CounterThread : public SyncThread
{
        Q_OBJECT
public:
        Counter *counter;

        CounterThread(QObject *parent) : SyncThread(parent)
        {
                counter = 0;
        }

        ~CounterThread()
        {
                // SyncThread will stop the thread on destruct, but since our
                //   atStop() function makes references to CounterThread's
                //   members, we need to shutdown here, before CounterThread
                //   destructs.
                stop();
        }

protected:
        virtual void atStart()
        {
                counter = new Counter;
        }

        virtual void atStop()
        {
                delete counter;
        }
};

We can then use it like this:

CounterThread *thread = new CounterThread;

// after this call, the thread is started and the Counter is ready
thread->start();

// let's start the counter with a 1 second interval
thread->call(thread->counter, "start", QVariantList() << 1);
...

// after some time passes, let's check on the value
int x = thread->call(thread->counter, "value").toInt();

// we're done with this thing
delete thread;

Do you see a mutex anywhere? I didn't think so.
---

Even without the call() function, SyncThread is still very useful for preparing objects in another thread, which you can then QObject::connect() to and use signals and slots like normal.


Constructor & Destructor Documentation

QCA::SyncThread::SyncThread ( QObject parent = 0  ) 

Standard constructor.

Parameters:
parent the parent object for this parent.

QCA::SyncThread::~SyncThread (  ) 

Calls stop() and then destructs.

Note:
Subclasses should call stop() in their own destructor


Member Function Documentation

virtual void QCA::SyncThread::atEnd (  )  [protected, pure virtual]

Reimplement this to perform your deinitialization.

virtual void QCA::SyncThread::atStart (  )  [protected, pure virtual]

Reimplement this to perform your initialization.

QVariant QCA::SyncThread::call ( QObject obj,
const QByteArray method,
const QVariantList &  args = QVariantList(),
bool *  ok = 0 
)

Calls a slot of an object in the thread.

This function will block until the slot has returned.

It is possible for the call to fail, for example if the method does not exist.

The arguments and return value of the call use QVariant. If the method has no return value (returns void), then the returned QVariant will be null.

Parameters:
obj the object to call the method on
method the name of the method (without the arguments or brackets)
args the list of arguments to use in the method call
ok if not 0, true is stored here if the call succeeds, otherwise false is stored here.

virtual void QCA::SyncThread::run (  )  [protected, virtual]

Starts the event loop and calls atStart and atStop as necessary.

Reimplemented from QThread.

void QCA::SyncThread::start (  ) 

Starts the thread, begins the event loop the thread, and then calls atStart() in the thread.

This function will block until atStart() has returned.

void QCA::SyncThread::stop (  ) 

Stops the event loop of the thread, calls atStop() in the thread, and instructs the thread to finish.

This function will block until the thread has finished.


Friends And Related Function Documentation

QCA_EXPORT bool invokeMethodWithVariants ( QObject obj,
const QByteArray method,
const QVariantList &  args,
QVariant ret,
Qt::ConnectionType  type = Qt::AutoConnection 
) [related]

Convenience method to invoke a method by name, using a variant list of arguments.

This function can be used as shown:

class TestClass : public QObject
{
    Q_OBJECT
    // ...
public slots:
    QString qstringMethod()  { return QString( "the result" ); };
    bool boolMethod( const QString & )  { return true; };
};

TestClass *testClass = new TestClass;
QVariantList args;

QVariant stringRes;
// calls testClass->qstringMethod() with no arguments ( since args is an empty list)
bool ret = QCA::invokeMethodWithVariants( testClass, QByteArray( "qstringMethod" ), args, &stringRes );
// ret is true (since call succeeded), stringRes.toString() is a string - "the result"

QVariant boolResult;
QString someString( "not important" );
args << someString;
// calls testClass->boolMethod( someString ), returning result in boolResult
ret = QCA::invokeMethodWithVariants( testClass1, QByteArray( "boolMethod" ), args, &boolResult );
// ret is true (since call succeeded), boolResult.toBool() is true.

Parameters:
obj the object to call the method on
method the name of the method (without the arguments or brackets)
args the list of arguments to use in the method call
ret the return value of the method (unchanged if the call fails)
type the type of connection to use
Returns:
true if the call succeeded, otherwise false

QCA_EXPORT QByteArray methodReturnType ( const QMetaObject obj,
const QByteArray method,
const QList< QByteArray argTypes 
) [related]

Convenience method to determine the return type of a method.

This function identifies the return type of a specified method. This function can be used as shown:

class TestClass : public QObject
{
    Q_OBJECT
    // ...
public slots:
    QString qstringMethod()  { return QString(); };
    bool boolMethod( const QString & )  { return true; };
};

QByteArray myTypeName;

TestClass testClass;
QList<QByteArray> argsList; // empty list, since no args

myTypeName = QCA::methodReturnType( testClass.metaObject(), QByteArray( "qstringMethod" ), argsList );
// myTypeName is "QString"

myTypeName = QCA::methodReturnType( testClass.metaObject(), QByteArray( "boolMethod" ), argsList );
// myTypeName is "", because there is no method called "boolMethod" that has no arguments

argsList << "QString"; // now we have one argument
myTypeName = QCA::methodReturnType( testClass.metaObject(), QByteArray( "boolMethod" ), argsList );
// myTypeName is "bool"

The return type name of a method returning void is an empty string, not "void"

Note:
This function is not normally required for use with QCA. It is provided for use in your code, if required.
Parameters:
obj the QMetaObject for the object
method the name of the method (without the arguments or brackets)
argTypes the list of argument types of the method
Returns:
the name of the type that this method will return with the specified argument types.
See also:
QMetaType for more information on the Qt meta type system.


The documentation for this class was generated from the following file:

Generated on Wed Apr 29 15:16:12 2009 for Qt Cryptographic Architecture by  doxygen 1.5.5