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Throttle scrollbar updates in TermControl to ~one per 8ms (#4608)
In addition to the below (original) description, this commit introduces a ThrottledFunc template that can throttle _any_ function. It applies that type to muffle updates to the scrollbar. --- Redo #3531 but without the bug that it caused (#3622) which is why it was reverted. I'm sorry if I explain this badly. If you don't understand a part, make sure to let me know and I will explain it better. ### Explanation How it worked before: `Terminal` signals that viewport changed -> `TermControl::_TerminalScrollPositionChanged` gets called on the terminal thread -> it dispatches work for later to be ran the UI thread to updates the scrollbar's values Why it's bad: * If we have many viewport changes, it will create a long stack of operations to run. Instead, we should just update the scroll bar with the most recent information that we know. * Imagine if the rate that the work gets pushed on the UI thread is greater than the rate that it can handle: it might freeze? * No need to be real time, we can wait just a little bit (8ms) to accumulate viewport changes before we actually change the scroll bar's value because it appears to be expensive (see perf below). Now: `Terminal` signals that viewport changed -> `TermControl::_TerminalScrollPositionChanged` gets called on the terminal thread -> it tells the `ScrollBarUpdater` about a new update -> the `ScrollBarUpdater` only runs one job (I don't know if that's the right term) on the UI thread at a time. If a job is already running but hasn't updated the scroll bar yet, it changes the setting in the already existing job to update the scroll bar with the new values. A job "waits" some time before doing the update to throttle updates because we don't need real time scroll bar updates. -> eventually, it updates the scroll bar If the user scrolls when a scroll bar update is pending, we keep the scroll bar's Maximum and Minimum but let the user choose its new Value with the `CancelPendingValueChange` method. ### Note Also I changed a little bit the code from the Terminal to notify the TermControl less often when possible. I tried to scroll with the scroll bar, with the mouse wheel. I tried to scroll while content is being outputted. I tried to reproduce the crash from #2248 without success (good). Co-authored-by: Leonard Hecker <[email protected]> Closes #3622
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| @@ -0,0 +1,54 @@ | ||
| // Copyright (c) Microsoft Corporation. | ||
| // Licensed under the MIT license. | ||
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| #pragma once | ||
| #include "pch.h" | ||
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| template<typename T> | ||
| class ThreadSafeOptional | ||
| { | ||
| public: | ||
| template<class... Args> | ||
| bool Emplace(Args&&... args) | ||
| { | ||
| std::lock_guard guard{ _lock }; | ||
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| bool hadValue = _inner.has_value(); | ||
| _inner.emplace(std::forward<Args>(args)...); | ||
| return !hadValue; | ||
| } | ||
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| std::optional<T> Take() | ||
| { | ||
| std::lock_guard guard{ _lock }; | ||
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| std::optional<T> value; | ||
| _inner.swap(value); | ||
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| return value; | ||
| } | ||
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| // Method Description: | ||
| // - If the optional has a value, then call the specified function with a | ||
| // reference to the value. | ||
| // - This method is always thread-safe. It can be called multiple times on | ||
| // different threads. | ||
| // Arguments: | ||
| // - f: the function to call with a reference to the value | ||
| // Return Value: | ||
| // - <none> | ||
| template<typename F> | ||
| void ModifyValue(F f) | ||
| { | ||
| std::lock_guard guard{ _lock }; | ||
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| if (_inner.has_value()) | ||
| { | ||
| f(_inner.value()); | ||
| } | ||
| } | ||
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| private: | ||
| std::mutex _lock; | ||
| std::optional<T> _inner; | ||
| }; |
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| /*++ | ||
| Copyright (c) Microsoft Corporation | ||
| Licensed under the MIT license. | ||
| Module Name: | ||
| - ThrottledFunc.h | ||
| Abstract: | ||
| - This module defines a class to throttle function calls. | ||
| - You create an instance of a `ThrottledFunc` with a function and the delay | ||
| between two function calls. | ||
| - The function takes an argument of type `T`, the template argument of | ||
| `ThrottledFunc`. | ||
| - Use the `Run` method to wait and then call the function. | ||
| --*/ | ||
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| #pragma once | ||
| #include "pch.h" | ||
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| #include "ThreadSafeOptional.h" | ||
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| template<typename T> | ||
| class ThrottledFunc : public std::enable_shared_from_this<ThrottledFunc<T>> | ||
| { | ||
| public: | ||
| using Func = std::function<void(T arg)>; | ||
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| ThrottledFunc(Func func, winrt::Windows::Foundation::TimeSpan delay) : | ||
| _func{ func }, | ||
| _delay{ delay } | ||
| { | ||
| } | ||
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| // Method Description: | ||
| // - Runs the function later with the specified argument, except if `Run` | ||
| // is called again before with a new argument, in which case the new | ||
| // argument will be instead. | ||
| // - For more information, read the "Abstract" section in the header file. | ||
| // Arguments: | ||
| // - arg: the argument to pass to the function | ||
| // Return Value: | ||
| // - <none> | ||
| winrt::fire_and_forget Run(T arg) | ||
| { | ||
| if (!_pendingCallArg.Emplace(arg)) | ||
| { | ||
| // already pending | ||
| return; | ||
| } | ||
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| auto weakThis = this->weak_from_this(); | ||
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| co_await winrt::resume_after(_delay); | ||
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| if (auto self{ weakThis.lock() }) | ||
| { | ||
| auto arg = self->_pendingCallArg.Take(); | ||
| if (arg.has_value()) | ||
| { | ||
| self->_func(arg.value()); | ||
| } | ||
| else | ||
| { | ||
| // should not happen | ||
| } | ||
| } | ||
| } | ||
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| // Method Description: | ||
| // - Modifies the pending argument for the next function invocation, if | ||
| // there is one pending currently. | ||
| // - Let's say that you just called the `Run` method with argument A. | ||
| // After the delay specified in the constructor, the function R | ||
| // specified in the constructor will be called with argument A. | ||
| // - By using this method, you can modify argument A before the function R | ||
| // is called with argument A. | ||
| // - You pass a function to this method which will take a reference to | ||
| // argument A and will modify it. | ||
| // - When there is no pending invocation of function R, this method will | ||
| // not do anything. | ||
| // - This method is always thread-safe. It can be called multiple times on | ||
| // different threads. | ||
| // Arguments: | ||
| // - f: the function to call with a reference to the argument | ||
| // Return Value: | ||
| // - <none> | ||
| template<typename F> | ||
| void ModifyPending(F f) | ||
| { | ||
| _pendingCallArg.ModifyValue(f); | ||
| } | ||
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| private: | ||
| Func _func; | ||
| winrt::Windows::Foundation::TimeSpan _delay; | ||
| ThreadSafeOptional<T> _pendingCallArg; | ||
| }; |
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