#include <QtCrypto>
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) |
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.
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.
QCA::SyncThread::SyncThread | ( | QObject * | parent = 0 |
) |
Standard constructor.
parent | the parent object for this parent. |
QCA::SyncThread::~SyncThread | ( | ) |
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.
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] |
void QCA::SyncThread::start | ( | ) |
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.
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.
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 |
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"
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 |