To detect a hung event loop, you need to wrap the operation that can hang the event loop, to detect when it takes too long. The “operation” is the QCoreApplication::notify member. It is called to deliver events to all event loops, in all threads. An event loop hang occurs when the code that processes an … Read more
They are added to queue and processed later: A JavaScript runtime contains a message queue, which is a list of messages to be processed. A function is associated with each message. When the stack is empty, a message is taken out of the queue and processed. The processing consists of calling the associated function (and … Read more
From the HTML specs, the most important point being made about this matter is in the task-source definition where we can read: Per its source field, each task is defined as coming from a specific task source. For each event loop, every task source must be associated with a specific task queue. Note Essentially, task … Read more
Your intuition is right that the event loop is something that embedders should have control over. However, it is also a fundamental abstract concept of the JavaScript programming model. V8’s solution is to provide a default implementation that embedders can override; you can find it in the “libplatform” component: https://chromium.googlesource.com/v8/v8/+/master/src/libplatform/default-platform.cc#140 See also Relationship between event … Read more
In the question, there existed a race condition between: The browser’s attempt to initialize the drop-down list, ready to have its selected index updated, and Your code to set the selected index Your code was consistently winning this race and attempting to set drop-down selection before the browser was ready, meaning that the bug would … Read more
The reasoning is that when the callbacks are always asynchronous instead of possibly asynchronous, it gives more consistent and reliable api to use. Consider the following code var pizza; browseStackOverflow().then(function(){ eatPizza(pizza); }); pizza = yesterdaysLeftovers; Now that snippet clearly assumes the onFulfilled will not be called right away and if that wasn’t the case we … Read more
In this case, there is no way to cancel the Future once it has actually started running, because you’re relying on the behavior of concurrent.futures.Future, and its docs state the following: cancel() Attempt to cancel the call. If the call is currently being executed and cannot be cancelled then the method will return False, otherwise … Read more
Why “1” is after “b”? The promise specification states that all promise .then() handlers must be called asynchronously after the call stack has emptied. Thus, both a and b, which are executed synchronously on the call stack will execute before any .then() handlers so 1 will always be after a and b. Some interesting reading: … Read more
I used to wonder a lot about the same! A GUI main loop looks like this, in pseudo-code: void App::exec() { for(;;) { vector<Waitable> waitables; waitables.push_back(m_networkSocket); waitables.push_back(m_xConnection); waitables.push_back(m_globalTimer); Waitable* whatHappened = System::waitOnAll(waitables); switch(whatHappened) { case &m_networkSocket: readAndDispatchNetworkEvent(); break; case &m_xConnection: readAndDispatchGuiEvent(); break; case &m_globalTimer: readAndDispatchTimerEvent(); break; } } } What is a “Waitable”? Well, it’s … Read more
When using Javascript promises, does the event loop get blocked? No. Promises are only an event notification system. They aren’t an operation themselves. They simply respond to being resolved or rejected by calling the appropriate .then() or .catch() handlers and if chained to other promises, they can delay calling those handlers until the promises they … Read more