Qt Cryptographic Architecture
Public Member Functions | Protected Member Functions | Friends | Related Symbols | List of all members
QCA::SyncThread Class Referenceabstract

#include <QtCrypto>

Collaboration diagram for QCA::SyncThread:
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Public Member Functions

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

Protected Member Functions

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

Friends

class Private
 

Related Symbols

(Note that these are not member symbols.)

QCA_EXPORT bool invokeMethodWithVariants (QObject *obj, const QByteArray &method, const QVariantList &args, QVariant *ret, Qt::ConnectionType type=Qt::AutoConnection)
 
QCA_EXPORT int 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, &QTimer::timeout, this, &Counter::t_timeout);
}
public slots:
void start(int seconds)
{
timer.setInterval(seconds * 1000);
timer.start();
}
int value() const
{
return x;
}
private Q_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;
}
};
Convenience class to run a thread and interact with it synchronously.
Definition qca_support.h:280

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;

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

◆ SyncThread()

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

Standard constructor.

Parameters
parentthe parent object for this parent.

◆ ~SyncThread()

QCA::SyncThread::~SyncThread ( )
override

Calls stop() and then destructs.

Note
Subclasses should call stop() in their own destructor

Member Function Documentation

◆ start()

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.

◆ stop()

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.

◆ call()

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

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
objthe object to call the method on
methodthe name of the method (without the arguments or brackets)
argsthe list of arguments to use in the method call
okif not 0, true is stored here if the call succeeds, otherwise false is stored here.

◆ atStart()

virtual void QCA::SyncThread::atStart ( )
protectedpure virtual

Reimplement this to perform your initialization.

◆ atEnd()

virtual void QCA::SyncThread::atEnd ( )
protectedpure virtual

Reimplement this to perform your deinitialization.

◆ run()

void QCA::SyncThread::run ( )
overrideprotected

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

Friends And Related Symbol Documentation

◆ methodReturnType()

QCA_EXPORT int 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
objthe QMetaObject for the object
methodthe name of the method (without the arguments or brackets)
argTypesthe 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.

◆ invokeMethodWithVariants()

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
objthe object to call the method on
methodthe name of the method (without the arguments or brackets)
argsthe list of arguments to use in the method call
retthe return value of the method (unchanged if the call fails)
typethe type of connection to use
Returns
true if the call succeeded, otherwise false

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