i have a public class , in that class i have a void which sets Clipboard.Text and i have a thread from which i call that func, everytime i call it i get
Current thread must be set to single thread apartment (STA) mode before OLE calls can be made. Ensure that your Main function has STAThreadAttribute marked on it.
I have tried the following :
Thread t = new Thread(Worker);
t.SetApartmentState(ApartmentState.STA);
t.Start();
But i still recieve error, i even tried [STAThread]
My function looks like this
public void Set(string s)
{
Clipboard.SetText(s);
}
I believe it is telling you put put the STAThread attribute on your main function, like so:
[STAThread]
static void Main()
{
// Your code
}
You said you tried STAThread, but was it on the main function or the function you're calling?
Related
I have an application consisting of an executable and several DLLs.
The exe links a dll statically. This dll creates a worker thread which instantiates a Q_GLOBAL_STATIC object (first access). So this object (derived from QObject) lives in this worker thread.
At program exit this object needs to be destroyed in the worker thread. But it is actually destroyed when the static dll gets unloaded, which is happening in the main thread.
How do I delete this global static object in the correct thread?
I tried manually deleting it when my worker thread finishes. But this results in a crash after my destructor returns.
You need to explicit call destructor on that object like this obj.~Test(); then after check if object is destroyed obj.isDestroyed() if it is not working.
Use QLibrary to load and unload dll ( https://doc.qt.io/archives/qt-4.8/qlibrary.html). Where in Q_GLOBAL_STATIC documentation(https://doc.qt.io/qt-5/qglobalstatic.html#destruction) it is mention that destructor will be called on unload of library or atexit() funciton of application.
I'd like to share my solution. To make it work, I introduced a simple private class which I use as a QGlobalStatic. This global object of this class holds the real singleton object and allows safe deletion of it in the correct thread.
The header file:
class MySingletonPrivate;
class MySingleton : public QObject
{
Q_OBJECT
public:
static MySingleton* instance();
static void deleteInstance();
protected:
MySingleton( QObject *parent = nullptr );
~MySingleton();
friend class MySingletonPrivate;
};
The cpp file:
class MySingletonPrivate
{
public:
MySingletonPrivate()
: inst( new MySingleton() )
{
QObject::connect( QThread::currentThread(), &QThread::finished, inst, &MySingleton::deleteLater );
}
~MySingletonPrivate()
{
Q_ASSERT( inst.isNull() );
}
MySingleton* instance() const
{
return inst;
}
private:
QPointer< MySingleton > inst;
};
Q_GLOBAL_STATIC( MySingletonPrivate, s_instance );
MySingleton* MySingleton::instance()
{
return s_instance->instance();
}
void MySingleton::deleteInstance()
{
delete s_instance->instance();
}
Using the signal QThread::finished the global instance is deleted at the end of the worker thread.
I left out the include instructions and the constructor and destructor implemention to make the answer shorter.
Of course, the first call to MySingleton::instance() must happen in the worker thread.
I need help to use the below piece of code to call Method1. There are no compilation issues but while running the code Method1 is not invoked. I searched the net a lot but didn't find a solution.
public static class Test12
{
public static Test12.ByteDelegate PropertyValue { get; set; }
public delegate byte[] ByteDelegate(byte p1, byte[] p2);
}
The above class has to be used like this:
class Abc
{
internal void Stat()
{
Test12.Propertyvalue = Method1;
}
private byte[] Method1(byte p1, byte[] p2)
{
byte[] abc = ...;
return abc;
}
}
If I am creating an instance of the delegate in stat method and using it like:
Method1(param1,param2);
Then the Method1 in invoked, but if I use it like this:
Test12.PropertyValue = Method1(param1,param2);
compiler is throwing an error saying missing typecast. Can anybody please tell me how to invoke Method1 using Test12.PropertyValue = Method1;?
You receive an error message because when you try to assign the method to the delegate you are using the following line of code:
test12.propertyvalue = method1(param1, param2);
Which firstly calls the method1 and then what it returns it's trying to assign to the delegate, and the error message occurs saying that you can't assign a byte array to a delegate, as #Jon said in the comment. They are different types so you can't assign one to another, at least not without a cast or a conversion method.
In order to invoke the method1 from the delegate, after you do the assignation like this:
test12.propertyvalue = method1;
you can simply call the delegate, as it would be your method:
test12.propertyvalue(param1 , param2);
// What is the technical reason behind this scenarios..?
You're trying to use a statement other than a declaration directly inside the class - rather than within a method. When did you expect the method to get called?
Basically all you can have directly within a type is a bunch of declarations - methods, variables, constructors, events, nested types etc. Method calls (or any other statements) which aren't part of a declaration have to be written within methods, constructors etc.
Method call statement can not be part of a class declaration, but only within Function members declarations scope, such as Methods, Properties, Constructors etc.
For example:
public class ExampleClass
{
private void SayHelloWorld()
{
Console.Writeline("Hello World!");
}
public void CallSayHelloWorldMethod()
{
this.SayHelloWorld();
}
}
At the above example you can see that I call the SayHelloWorld method within the CallSayHelloWorldMethod metod.
Update:
The closest thing I can think of in your case is to use the class's constructor where your method call will be executed as soon as you'll instantiate your class:
public class ExampleClass
{
//The class constructor
public ExampleClass()
{
this.SayHelloWorld();
}
private void SayHelloWorld()
{
Console.Writeline("Hello World!");
}
}
And when you instantiating it, it will be immediately called:
//Your method call will be executed here
ExampleClass exampleClass = new ExampleClass();
You have a few problems... This won't even compile as you are trying to call the method obj.m1() in the class definition.
A obj = new A();
obj.m1(); // Why this code wont work??? --> This must be inside a method
When you create an instance of a class it will create a new member variable called obj which is an instance of A --> A obj = newA() above;
You will now be able to call obj's methods as in your second example.
Also, in order to get this to compile you will need to fix the m2 method:
public void m2() { //--> should have a curly brace
obj.m1(); // But This will work.
}
I've subclassed my Qthread so I can implement my code in run() method. I have to pass it some parameters,
I tried it like this, so what's wrong in here?
class QMyThread :
public QThread
{
public:
QMyThread();
~QMyThread(void);
virtual void start(FILE *data, int sock, int bits);
protected:
virtual void run(FILE *data, int sock, int bits);
};
run method;
void QMyThread::run(FILE *data, int sock, int bits)
{
//do stuff
}
start the thread:
QMyThread *thread;
thread->start(datafile, sockint, bitsint);
first it says the thread might not be initialized and then it crashes in the start() method with SIGSEGV error. Anyone can help me?
You shouldn't be subclassing the QThread class as this is no longer the recommended way of using QThread.
For more information http://qt-project.org/doc/qt-4.8/qthread.html
To answer your question, couldn't you just make those parameters members of your class and assign their values through setters or its contructor?
You should do this instead:
QMyThread thread;
thread.start(...)
You created a pointer to a thread and did not new it. I frankly see no reason for a pointer here, you can just create a normal variable and call a method on it.
If you do want a pointer, then use std::unique_ptr in C++11 or boost::unique_ptr
std::unique_ptr<QMyThread> thread;
thread->start(...);
EDIT:
You should really just create a QThread * thread = new QThread(this); as per the documentation.
How about using the QMetaObject class to pass the parameters to worker class. You can try like this:
QMetaObject::invokeMethod(worker, "methodName", Q_ARG(QString, "ParameterQStringValue");
Note this method will work if methodName is a slot and you use the new way of creating threads: https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/
You can specify different parameters using Q_ARG macro up to 9 (http://doc.qt.io/qt-5/qmetaobject.html#details). If you need more parameters, then I suggest you to create the QVector with a structure and pass it to QMetaObject::invokeMethod as the parameter.
The QFuture class has methods such as cancel(), progressValue(), etc. These can apparently be monitored via a QFutureWatcher. However, the documentation for QtConcurrent::run() reads:
Note that the QFuture returned by
QtConcurrent::run() does not support
canceling, pausing, or progress
reporting. The QFuture returned can
only be used to query for the
running/finished status and the return
value of the function.
I have looked in vain for what method actually can create a QFuture that can be cancelled and report progress for a single long-running operation. (It looks like maybe QtConcurrent::map() and similar functions can, but I just have a single, long-running method.)
(For those familiar with .Net, something like the BackgroundWorker class.)
What options are available?
Though it's been a while since this question was posted and answered I decided to add my way of solving this problem because it is rather different from what was discussed here and I think may be useful to someone else. First, motivation of my approach is that I usually don't like to invent own APIs when framework already has some mature analogs. So the problem is: we have a nice API for controlling background computations represented by the QFuture<>, but we have no object that supports some of the operations. Well, let's do it. Looking on what's going on inside QtConcurrent::run makes things much clearer: a functor is made, wrapped into QRunnable and run in the global ThreadPool.
So I created generic interface for my "controllable tasks":
class TaskControl
{
public:
TaskControl(QFutureInterfaceBase *f) : fu(f) { }
bool shouldRun() const { return !fu->isCanceled(); }
private:
QFutureInterfaceBase *fu;
};
template <class T>
class ControllableTask
{
public:
virtual ~ControllableTask() {}
virtual T run(TaskControl& control) = 0;
};
Then, following what is made in qtconcurrentrunbase.h I made q-runnable for running this kind of tasks (this code is mostly from qtconcurrentrunbase.h, but slightly modified):
template <typename T>
class RunControllableTask : public QFutureInterface<T> , public QRunnable
{
public:
RunControllableTask(ControllableTask<T>* tsk) : task(tsk) { }
virtial ~RunControllableTask() { delete task; }
QFuture<T> start()
{
this->setRunnable(this);
this->reportStarted();
QFuture<T> future = this->future();
QThreadPool::globalInstance()->start(this, /*m_priority*/ 0);
return future;
}
void run()
{
if (this->isCanceled()) {
this->reportFinished();
return;
}
TaskControl control(this);
result = this->task->run(control);
if (!this->isCanceled()) {
this->reportResult(result);
}
this->reportFinished();
}
T result;
ControllableTask<T> *task;
};
And finally the missing runner class that will return us controllable QFututre<>s:
class TaskExecutor {
public:
template <class T>
static QFuture<T> run(ControllableTask<T>* task) {
return (new RunControllableTask<T>(task))->start();
}
};
The user should sublass ControllableTask, implement background routine which checks sometimes method shouldRun() of TaskControl instance passed to run(TaskControl&) and then use it like:
QFututre<int> futureValue = TaskExecutor::run(new SomeControllableTask(inputForThatTask));
Then she may cancel it by calling futureValue.cancel(), bearing in mind that cancellation is graceful and not immediate.
I tackled this precise problem a while ago, and made something called "Thinker-Qt"...it provides something called a QPresent and a QPresentWatcher:
http://hostilefork.com/thinker-qt/
It's still fairly alpha and I've been meaning to go back and tinker with it (and will need to do so soon). There's a slide deck and such on my site. I also documented how one would change Mandelbrot to use it.
It's open source and LGPL if you'd like to take a look and/or contribute. :)
Yan's statement is inaccurate. Using moveToThread is one way of achieving the proper behavior, but it not the only method.
The alternative is to override the run method and create your objects that are to be owned by the thread there. Next you call exec(). The QThread can have signals, but make sure the connections are all Queued. Also all calls into the Thread object should be through slots that are also connected over a Queued connection. Alternatively function calls (which will run in the callers thread of execution) can trigger signals to objects that are owned by the thread (created in the run method), again the connections need to be Queued.
One thing to note here, is that the constructor and destructor are running in the main thread of execution. Construction and cleanup need to be performed in run. Here is an example of what your run method should look like:
void MythreadDerrivedClass::run()
{
constructObjectsOnThread();
exec();
destructObjectsOnThread();
m_waitForStopped.wakeAll();
}
Here the constructObjectsOnThread will contain the code one would feel belongs in the constructor. The objects will be deallocated in destructObjectsOnThread. The actual class constructor will call the exit() method, causing the exec() to exit. Typically you will use a wait condition to sit in the destructor till the run has returned.
MythreadDerivedClass::~MythreadDerivedClass()
{
QMutexLocker locker(&m_stopMutex);
exit();
m_waitForStopped.wait(locker.mutex(), 1000);
}
So again, the constructor and destructor are running in the parent thread. The objects owned by the thread must be created in the run() method and destroyed before exiting run. The class destructor should only tell the thread to exit and use a QWaitCondition to wait for the thread to actually finish execution. Note when done this way the QThread derived class does have the Q_OBJECT macro in the header, and does contain signals and slots.
Another option, if you are open to leveraging a KDE library, is KDE's Thread Weaver. It's a more complete task based multitasking implementation similar QtConcurrentRun in that it leverages a thread pool. It should be familiar for anyone from a Qt background.
That said, if you are open to a c++11 method of doing the same thing, I would look at std::async. For one thing, you will no longer have any dependance on Qt, but the api also makes more clear what is going on. With MythreadDerivedClass class inheriting from QThread, the reader gets the impression that MythreadDerivedClass is a thread (since it has an inheritance relationship), and that all its functions run on a thread. However, only the run() method actually runs on a thread. std::async is easier to use correctly, and has fewer gotcha's. All our code is eventually maintained by someone else, and these sorta things matter in the long run.
C++11 /w QT Example:
class MyThreadManager {
Q_OBJECT
public:
void sndProgress(int percent)
void startThread();
void stopThread();
void cancel() { m_cancelled = true; }
private:
void workToDo();
std::atomic<bool> m_cancelled;
future<void> m_threadFuture;
};
MyThreadedManger::startThread() {
m_cancelled = false;
std::async(std::launch::async, std::bind(&MyThreadedManger::workToDo, this));
}
MyThreadedManger::stopThread() {
m_cancelled = true;
m_threadfuture.wait_for(std::chrono::seconds(3))); // Wait for 3s
}
MyThreadedManger::workToDo() {
while(!m_cancelled) {
... // doWork
QMetaInvoke::invokeMethod(this, SIGNAL(sndProgress(int)),
Qt::QueuedConnection, percentDone); // send progress
}
}
Basically, what I've got here isn't that different from how your code would look like with QThread, however, it is more clear that only workToDo() is running on the thread and that MyThreadManager is only managing the thread and not the thread itself. I'm also using MetaInvoke to send a queued signal for sending our progress updates with takes care of the progress reporting requirement. Using MetaInvoke is more explicit and always does the right thing (doesn't matter how you connect signals from your thread managers to other class's slots). You can see that the loop in my thread checks an atomic variable to see when the process is cancelled, so that handles the cancellation requirement.
Improve #Hatter answer to support Functor.
#include <QFutureInterfaceBase>
#include <QtConcurrent>
class CancellationToken
{
public:
CancellationToken(QFutureInterfaceBase* f = NULL) : m_f(f){ }
bool isCancellationRequested() const { return m_f != NULL && m_f->isCanceled(); }
private:
QFutureInterfaceBase* m_f;
};
/*== functor task ==*/
template <typename T, typename Functor>
class RunCancelableFunctorTask : public QtConcurrent::RunFunctionTask<T>
{
public:
RunCancelableFunctorTask(Functor func) : m_func(func) { }
void runFunctor() override
{
CancellationToken token(this);
this->result = m_func(token);
}
private:
Functor m_func;
};
template <typename Functor>
class RunCancelableFunctorTask<void, Functor> : public QtConcurrent::RunFunctionTask<void>
{
public:
RunCancelableFunctorTask(Functor func) : m_func(func) { }
void runFunctor() override
{
CancellationToken token(this);
m_func(token);
}
private:
Functor m_func;
};
template <class T>
class HasResultType
{
typedef char Yes;
typedef void *No;
template<typename U> static Yes test(int, const typename U::result_type * = 0);
template<typename U> static No test(double);
public:
enum { Value = (sizeof(test<T>(0)) == sizeof(Yes)) };
};
class CancelableTaskExecutor
{
public:
//function<T or void (const CancellationToken& token)>
template <typename Functor>
static auto run(Functor functor)
-> typename std::enable_if<!HasResultType<Functor>::Value,
QFuture<decltype(functor(std::declval<const CancellationToken&>()))>>::type
{
typedef decltype(functor(std::declval<const CancellationToken&>())) result_type;
return (new RunCancelableFunctorTask<result_type, Functor>(functor))->start();
}
};
User example:
#include <QDateTime>
#include <QDebug>
#include <QTimer>
#include <QFuture>
void testDemoTask()
{
QFuture<void> future = CancelableTaskExecutor::run([](const CancellationToken& token){
//long time task..
while(!token.isCancellationRequested())
{
qDebug() << QDateTime::currentDateTime();
QThread::msleep(100);
}
qDebug() << "cancel demo task!";
});
QTimer::singleShot(500, [=]() mutable { future.cancel(); });
}
For a long running single task, QThread is probably your best bet. It doesn't have build-in progress reporting or canceling features so you will have to roll your own. But for simple progress update it's not that hard. To cancel the task, check for a flag that can be set from calling thread in your task's loop.
One thing to note is if you override QThread::run() and put your task there, you can't emit signal from there since the QThread object is not created within the thread it runs in and you can't pull the QObject from the running thread. There is a good writeup on this issue.