Qt signal slot thread context

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22 Apr 2016 [Interest] Qt signal overhead (same thread, direct connection) >From Qt doc: " When a signal is emitted, the slots connected to it are usually is on a ARM device specially in this kind of > performance se

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Qt uses signals and slots normally in a single thread, so calling a signal will call a slot in the same thread signal called. Is it any way to use a signal-slot mechanism to pass a message to qt thread ( so slot will be called later in specified thread's context )? The 'connect' needs at argument 2 and 4 a function pointer.

Qt::QueuedConnection forces Qt to "delay" invocation of the receiving signal/slot by posting an event in the event queue of the thread the receiving object resides in. When the signal/slot is actually executed it is done in the receiver object's thread. Qt::AutoConnection (the default parameter) is a bit smarter. When a signal is emitted Qt @JadeN001 said in signal and slots in movetothread: as i know slot will execute on thread where receiver's object is created in directconnection senario. As far as I know this is completely wrong. This is only the case with queued connection. Direct connection will mean that the slot is executed in the thread where the signal is emitted.

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.

@RudolfVonKrugstein Since setContextProperty is not a slot, and you should not rely on functions to be thread-safe (most of Qt's API is reentrant, not TS) you could connect a lambda to your signal (assuming you have C++11 support), that will do the setContextProperty invocation. 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. However, since 5.2 there is an overload which adds a "context object". When that object is destroyed, the connection is broken (the context is also used for the thread affinity: the lambda will be called in the thread of the event loop of the object used as context). Disconnecting in Qt 5 Signals and Slots Across Threads. Qt supports these signal-slot connection types : Auto  Signals and slots are made possible by Qt's meta-object system. important, as providing the context ensures that the receiver is executed in the context thread. This is what threads are for — concurrency within one single process. Sometimes you want to do more than just running a method in the context of another thread. Connect the signals to the GUI thread's slots using queued signa Take a look at Signals and slots across threads. If you always use signals and slots to communicate with the worker thread, Qt handles the 

Dose the slot's thread response the signal after the time slice of signal thread over? If using QThread::yieldCurrentThread() after sending the signal, does the context switch still depend on the QThread::priority()? But if both threads are QThread::NormalPrority, is random? If a thread has only a slot ( without any other function,just void on

That's just a pattern in Qt -- when setting up connections for sub-objects, you typically connect them to slots on this object, hence this is probably the most common context. However, in general, you may also end up with something like Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type. Connect the signals to the GUI thread's slots using queued signal/slot connections. Permanent: Have an object living in another thread and let it perform different tasks upon request. This means communication to and from the worker thread is required. Qt uses the timer's thread affinity to determine which thread will emit the timeout () signal. Because of this, you must start and stop the timer in its thread; it is not possible to start a timer from another thread.

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You can invoke that slot by connecting a signal to it from the main thread, or by using QMetaObject::invokeMethod. In the latter case, don't forget to include the Qt::QueuedConnection flag, otherwise you make a direct method call and your slot won't be executed in the new threads' context, but in the main threads' context. [/quote] written. If Qt::QueuedConnection: 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. See ConnectionType-enum for more options. The problem is not really from which thread you emit the signal, it's more from which thread the slot is being invoked. Qt uses signals and slots normally in a single thread, so calling a signal will call a slot in the same thread signal called. Is it any way to use a signal-slot mechanism to pass a message to qt thread ( so slot will be called later in specified thread's context )? The 'connect' needs at argument 2 and 4 a function pointer. emitting a signal to a direct connection within the same thread will execute the slot immediately, just like a simple function call. emitting a signal to a queued connection within the same thread will enqueue the call into the threads event loop, thus the execution will always happen delayed. QObject based class has a queued connection to itself Qt::DirectConnection: This slot is invoked immediately when the signal is emitted. The slot is executed in the signaling thread. ␡ The Qt framework brings a flexible message exchange mechanism through three concepts: signals, slots, and connections:A signal is a message sent by an This website uses cookies and other tracking technology to However, since 5.2 there is an overload which adds a "context object". When that object is destroyed, the connection is broken (the context is also used for the thread affinity: the lambda will be called in the thread of the event loop of the object used as context). Disconnecting in Qt 5 An overview of Qt’s signals and slots inter-object communication mechanism. Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks.