Qrunnable vs qthread
A program in execution is known as a process. The process can be divided into multiple subprocesses. For example, Microsoft Word is a process. At the same time, it checks for the spelling mistake and grammar. That is a subprocess. These subprocesses are known as threads. Multithreading is the process of executing multiple threads simultaneously. Threaded applications can be built using different programming languages.
Runnable and Thread are associated with Java programming. There are two methods in Java to create a thread by implementing a Runnable interface or extending the Thread class.
When implementing Runnable, many threads can share the same thread object while in Extending Thread class, each thread has a unique object associated with it. That is the key difference between Runnable and Thread.
Overview and Key Difference 2. What is Runnable 3. What is Thread 4. Similarities Between Runnable and Thread 5. A thread goes through some states. After the start method calls on a new thread, it becomes runnable. If the thread scheduler selects the thread, it transits to the running state. The thread is waiting for the state if that thread is waiting for another thread to perform a task. After the thread completes the work, it goes to the termination state. Figure Java Program to create a thread using Runnable interface.
According to the above program, the class Runnable Demo implements the Runnable interface. The run method is inside the class that implements Runnable interface. It is the entry point for the thread.
The logic is in the run method. In the main program, a thread is created by defining an object that instantiated from Runnable Demo class.Thread Support in Qt Synchronizing Threads. Qt offers many classes and functions for working with threads. Below are four different approaches that Qt programmers can use to implement multithreaded applications. QThread is the foundation of all thread control in Qt.
Each QThread instance represents and controls one thread. QThread can either be instantiated directly or subclassed. Instantiating a QThread provides a parallel event loop, allowing QObject slots to be invoked in a secondary thread.
Subclassing a QThread allows the application to initialize the new thread before starting its event loop, or to run parallel code without an event loop. See the QThread class reference and the threading examples for demonstrations on how to use QThread. Creating and destroying threads frequently can be expensive. To reduce this overhead, existing threads can be reused for new tasks.
QThreadPool is a collection of reuseable QThreads. When a thread becomes available, the code within QRunnable::run will execute in that thread. Each Qt application has a global thread pool, which is accessible through QThreadPool::globalInstance. This global thread pool automatically maintains an optimal number of threads based on the number of cores in the CPU.
However, a separate QThreadPool can be created and managed explicitly. The Qt Concurrent module provides high-level functions that deal with some common parallel computation patterns: map, filter, and reduce. Unlike using QThread and QRunnablethese functions never require the use of low-level threading primitives such as mutexes or semaphores. Instead, they return a QFuture object which can be used to retrieve the functions' results when they are ready. Qt Concurrent 's map, filter and reduce algorithms automatically distribute computation across all available processor cores, so applications written today will continue to scale when deployed later on a system with more cores.
This module also provides the QtConcurrent::run function, which can run any function in another thread. However, QtConcurrent::run only supports a subset of features available to the map, filter and reduce functions. The QFuture can be used to retrieve the function's return value and to check if the thread is running. See the Qt Concurrent module documentation for details on the individual functions.
Each WorkerScript instance can have one. When WorkerScript. When the script finishes running, it can send a reply back to the GUI thread which will invoke the WorkerScript.
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Using a WorkerScript is similar to using a worker QObject that has been moved to another thread. Data is transferred between threads via signals.Please share with friends and colleagues! A common problem when building GUI applications is "locking up" of the interface when attempting to perform long-running background tasks.
In this tutorial I'll cover one of the simplest ways to achieve concurrent execution in PyQt. Applications based on Qt like most GUI applications are event based. This means that execution is driven in response to user interaction, signals and timers.
In an event-driven application, clicking on a button creates an event which your application subsequently handles to produce some expected output. Events are pushed onto and taken off an event queue and processed sequentially. The event loop is started by calling. By default, any execution triggered by the event loop will also run synchronously within this thread. In practise this means that any time your PyQt application spends doing something in your code, window communication and GUI interaction are frozen.
If what you're doing is simple, and returns control to the GUI loop quickly, this freeze will be imperceptible to the user. To your user the application will appear to be unresponsive because it is.
Because your app is no longer communicating with the OS, on MacOS X if you click on your app you will see the spinning wheel of death.
And, nobody wants that. The solution is simple: get your work out of the GUI thread and into another thread. PyQt via Qt provides an straightforward interface to do exactly that.
To demonstrate multi-threaded execution we need an application to work with. Below is a minimal stub application for PyQt which will allow us to demonstrate multithreading, and see the outcome in action.
Simply copy and paste this into a new file, and save it with an appropriate filename like multithread. The remainder of the code will be added to this file there is also a complete working example at the bottom if you're impatient. You should see a demonstration window with a number counting upwards.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. The QRunnable class and the QtConcurrent::run function are well suited to situations where we want to perform some background processing in one or more secondary threads without needing the full power and flexibility provided by QThread.
QThread can run an event loop, QRunnable doesn't have one so don't use it for tasks designed to have an event loop. Also, not being a QObject, QRunnable has no built-in means of explicitly communicating something to other components; you have to code that by hand, using low-level threading primitives like a mutex-guarded queue for collecting results, etc.
Using QThread you can use signals and slots which are thread safe. Learn more. Asked 6 years, 10 months ago. Active 1 year, 4 months ago. Viewed 4k times. What are the differences between QThreads and QRunnable? Videos can be found here: Part 1Part 2. Candela Oct 11 '19 at Active Oldest Votes.
Erik Kaju Erik Kaju 2, 3 3 gold badges 14 14 silver badges 26 26 bronze badges. This answer would be useful if it explained "full power and flexibility provided by QThread", because it suggests you should default to using QRunnable, and use QThread only when you need An event loop?
Alexandra Anghelescu Alexandra Anghelescu 1 1 silver badge 4 4 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook.
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Triage needs to be fixed urgently, and users need to be notified upon…. Dark Mode Beta - help us root out low-contrast and un-converted bits. Visit chat.A thread can be defined in two ways.
First, by extending a Thread class that has already implemented a Runnable interface. Second, by directly implementing a Runnable interface. When you define a thread by extending Thread class you have to override the run method in Thread class.
When you define a thread implementing a Runnable interface you have to implement the only run method of Runnable interface. The basic difference between Thread and Runnable is that each thread defined by extending Thread class creates a unique object and get associated with that object. On the other hand, each thread defined by implementing Runnable interface shares the same object.
Let us observe some other differences between Thread and Runnable with the help of comparison chart shown below:. Basis for Comparison Thread Runnable Basic Each thread creates a unique object and gets associated with it. Multiple threads share the same objects.
Memory As each thread create a unique object, more memory required. As multiple threads share the same object less memory is used.
Extending In Java, multiple inheritance not allowed hence, after a class extends Thread class, it can not extend any other class. If a class define thread implementing the Runnable interface it has a chance of extending one class. Use A user must extend thread class only if it wants to override the other methods in Thread class. If you only want to specialize run method then implementing Runnable is a better option.
Coupling Extending Thread class introduces tight coupling as the class contains code of Thread class and also the job assigned to the thread Implementing Runnable interface introduces loose coupling as the code of Thread is separate form the job of Threads. Thread is a class in java. The Thread class extends an Object class, and it implements Runnable interfaces. The Thread class has constructors and methods to create and operate on the thread.As discussed in Java multi-threading article we can define a thread in the following two ways:.
In the first approach, Our class always extends Thread class. There is no chance of extending any other class. Hence we are missing Inheritance benefits. In the second approach, while implementing Runnable interface we can extends any other class. Hence we are able to use the benefits of Inheritance. Because of the above reasons, implementing Runnable interface approach is recommended than extending Thread class.
Multithreading PyQt applications with QThreadPool
The significant differences between extending Thread class and implementing Runnable interface:. This article is contributed by Bishal Kumar Dubey. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Writing code in comment?
Please use ide. As discussed in Java multi-threading article we can define a thread in the following two ways: By extending Thread class By implementing Runnable interface In the first approach, Our class always extends Thread class. Load Comments.In java language, as we all know that there are two ways to create threads.
One using Runnable interface and another by extending Thread class. There has been a good amount of debate on which is better way. Well, I also tried to find out and below is my learning. The issue is that at construction time, a Thread is added to a list of references in an internal thread table. If you know something more, please put that in comments section and I will include in post content.
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At point 4, how can a task non-run metho inside Thread extending class, still need to run in thread only. It can still be executed within a main thread. Could u pls elaborate? By implementing Runnable interface, we can only override the run method. But when we extend Thread class, we can use many methods based on our requirements. If we want to make our class as a thread, we can always go for extending the Thread class rather than implementing Runnable interface.
As per my understanding, Thread is a curse in java. If you create multiple threads then there would be a chance of memory overhead and hence the performance of the app will go down. As per my knowledge, the advantage is — when there are multiple threads then, memory usage would be more in case of extends Thread. Because, each of your threads contains unique object associated with it.
Where as, memory usage would be less in case of implements Runnable. Because, many threads can share the same runnable instance. You are right Gopi. Point 5 state the same thought as you.
Many threads can share the same Thread object, same as Runnable instance. Difference between Thread and Runnable I found is, Thread class provides apis to configure Thread instance based on your need. If you extends Thread class, then 1. There are apis available in Thread class which is not avaialbe in Runnable.
Those apis helps developers to configure Thread properties. If you call A1. And A1. By extending Thread, each of your threads has a unique object associated with it, whereas implementing Runnable, many threads can share the same runnable instance.
The code is misleading.