1. Qthread Signal Slot Example
2. Qthread Signal Slot
3. Qt Signal Slot Qthread
4. Qthreadpool Signal Slot

Cross-thread signal-slot connections are implemented by dispatching a QMetaCallEvent to the target object. A QObject instance can be moved to a thread, where it will process its events, such as timer events or slot/method calls. To do work on a thread, first create your own worker class that derives from QObject. Then move it to the thread. Signals & Slots, Signals and slots are made possible by Qt's meta-object system. To one signal, the slots will be executed one after the other, in the order they have valueChanged, and it has a slot which other objects can send signals to. The context object provides information about in which thread the receiver should be executed. Since a QThread's affinity is the thread that created it, slots executing within it (that is methods of your QThread) will execute in the QThread's parent thread's context when responding to signals. In other words, if you 'post' to a QThread method via a signal, you're not doing work in that QThread as you'd probably expect. Whenever is star is drawn by the worker thread, it will emit a signal that is connected to the addImage slot. This slot is called with a QRect value, indicating where the star should be placed in the pixmap held by the viewer label, and an image of the star itself.

how in BOOST send a signal in a thread and have the corresponding slot executed in another thread?

In Qt for instance if you emit a signal in a thread other that the GUI thread, the signal is enqueued and executed later in the GUI thread, is there a way to do that with boost?

thanks

For an event loop use boost::asio::io_service. You can post tasks inside this object and have another thread execute them, in a thread safe way:

Messaging and Signaling in C++, But as this blog post is more on signaling then system events. Qt signal/slot implementation is thread safe, so that you can use it to send messages important, as anything UI related should run in the main thread of Qt, anything that I use this in a different program to have one widget for editing flag like Almost all classes provided by Boost.Signals2 are thread safe and can be used in multithreaded applications. For example, objects of type boost::signals2::signal and boost::signals2::connection can be accessed from different threads. On the other hand, boost::signals2::shared_connection_block is not thread safe.

Not directly, because boost does not provide an event loop.

To have a signal handled in another thread, that another thread needs to be checking the queue of handlers it should run and execute them (which usually means some kind of event-loop). Boost does not provide one, so you'll need to get it from elsewhere or write it.

If you have an event-loop, that does not provide signals, (or implement some simple solution with queues) you should be able to (ab)use boost.signals2 (not boost.signals, because that version is not thread-safe) by overriding the operator+= to wrap each handler in something, that will queue it for execution in the other thread. You might even be able to implement it for signals with return values (which is not supported by Qt, but is supported by boost), but you'll have to be careful to avoid dead-lock.

[PDF] Boost.Signals2, Signals2 library is an implementation of a managed signals and slots system. This documentation describes a thread-safe variant of the original Boost. so we put 'Hello' into a group that must be executed before the group possible to set up tracking in a post-constructor which is called after the object has been created​ To have a signal handled in another thread, that another thread needs to be checking the queue of handlers it should run and execute them (which usually means some kind of event-loop). Boost does not provide one, so you'll need to get it from elsewhere or write it.

Signals & Slots, Signals and slots are made possible by Qt's meta-object system. to one signal, the slots will be executed one after the other, in the order they have valueChanged() , and it has a slot which other objects can send signals to. The context object provides information about in which thread the receiver should be executed. Special behavior for C++: If a thread is sent a signal using pthread_kill() and that thread does not handle the signal, then destructors for local objects may not be executed. Usage notes. The SIGTHSTOP and SIGTHCONT signals can be issued by this function. pthread_kill() is the only function that can issue SIGTHSTOP or SIGTHCONT. Returned value

Chila's answer is correct, but it's missing one important thing:A boost::thread object will only call the function its passed once. Since the boost::io_service has no work to do until the signal is emitted, the thread will finish immediately. To counter this there is a boost::asio::io_service::work class.Before you call the run() method of the io_service you should create a work object and pass it the io_service:

Note: At the time of writing (boost 1.67) this method is already deprecated and you are supposed to use io_context::executor_work_guard (basically same functionality as io_service::work). I was not able to compile when using the new method though, and the work solution is still working in boost 1.67.

Qthread Signal Slot Example

Slots, It also implements a few conditional (event) related classes. Qt - SigSlot - Boost Libraries Qt was the original signal/slots implementation, but it Sigslot and Boost on the other hand are pure ISO C++, but both have some disadvantages. None of these are thread-safe and it can be somewhat inconvenient manually Qt documentation states that signals and slots can be direct, queued and auto. It also stated that if object that owns slot 'lives' in a thread different from object that owns signal, emitting such signal will be like posting message - signal emit will return instantly and slot method will be called in target thread's event loop.

For some reason, the assignment operator of boost::asio::executor_work_guard<boost::asio::io_context::executor_type> is deleted, but you still can construct it.

Qthread Signal Slot

Here's my version of the code that posts some movable Event object and processes it on the thread running io_context::run():

It requires C++14 and was tested with VS2017 and GCC 6.4 with thread & memory sanitizers.

Observer pattern with Stl, boost and qt, A comparison between the Qt signal and slot mechanism and some Each slot is a potential callback ○ Adds more run-time introspection, The Synapse library ○ Another signals/slot like library ○ Submitted to Very similar to boost::​signals2 ○ Have the ability to transfer control between threads 29; 30. So, when the thread is created from the create_thread method it will call the io_service::run method and it passes the io_service object as an argument. Typically one io_service object can be used with multiple socket objects.

QThreads: Are You Using Them Wrong?, Show related SlideShares at end The Basics of QThread QThread manages one thread of execution ○ The Signal Slot Connections and Threads ○ Qt::​DirectConnection have same thread affinity: Direct ○ If objects have different thread It implies you want to send cross-thread signals to yourself. Direct Connection The slot is invoked immediately, when the signal is emitted. The slot is executed in the emitter's thread, which is not necessarily the receiver's thread. Queued Connection The slot is invoked when control returns to the event loop of the receiver's thread. The slot is executed in the receiver's thread.

What do I do if a slot is not invoked?, A practical checklist to debug your signal/slot connections that an event loop is running in the thread the receiver has affinity with;; that all the arguments Using this signal is very easy – it just acts like a flag, but you can wait for it as well as read it. The following unit test (also in GitHub) shows how the signal makes it easy for threads to set gates on each other. Note that the final signal in this example could have been done with thread.join(), but wasn’t for the purposes of the test.

Qt Signal Slot Qthread

[Boost-users] Signals2 benchmark, I want to test it against boost::signals2 to get an idea of how well it performs. Suppose one thread disconnects a slot while another fires a signal Each Signal-type has its own corresponding vector of slots defined within the Emitter. the copy being made instead of every slot being called and executed. POSIX requires that signal is thread-safe, and specifies a list of async-signal-safe library functions that may be called from any signal handler. Signal handlers are expected to have C linkage and, in general, only use the features from the common subset of C and C++. It is implementation-defined if a function with C++ linkage can be used as a

Qthreadpool Signal Slot

Comments

• THX for this very helpfull sample ! Since boost::signal is deprecated I have to use boost::signals2::signal<>.