[DefApp] Move from Monarch multi instance servers to Peasant single instance servers

[leonMSFT]

• Monarch no longer sets itself up as a CTerminalHandoff multi instance server by default
• In fact, CTerminalHandoff will only ever be a single instance server
• When COM needs a CTerminalHandoff, it launches wt.exe -embedding, which gets picked up by the Monarch and then gets handed off to itself/peasant depending on user settings.
• Peasant now recognizes the -embedding commandline and will start a CTerminalHandoff single instance listener, and receives the connection into a new tab.

Closes #10358, #9475

[DHowett]

LOVE IT. IT MAKES SO MUCH SENSE

[zadjii-msft]

@msftbot make sure @miniksa signs off on this

[ghost]

Hello @zadjii-msft!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I'll only merge this pull request if it's approved by @miniksa

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".

[zadjii-msft]

Hokay so lemme get this straight:

1. COM creates a wt -embedding process to try and host the incoming connection
2. that wt automatically tosses the commandline to the Monarch to have it deal with it.
3. The monarch will then either

• Toss the commandline wt -embedding to the appropriate peasant, who then
  • starts the COM server
  • accepts the connection
  • stops the server
  • opens the tab
• Or the monarch decides that this connection should be a new peasant (a new window)
  • the new window opens
  • starts the server, accepts the connection, ... opens the tab

all based on what we already had.

That's fricken amazing.

[miniksa]

It's pretty close. Just a few questions. I don't feel it is fair for me to block or sign though because I helped you debug and coauthor some of this. Hopefully @DHowett or @lhecker will do the second after we can look at these comments.

(it's otherwise fine from my pov)

[miniksa]

Something is up here and I'm not certain what it is.

It worries me that you covered one definition of lock (since the lambda captured everything) with another more local definition of the same thing.

The inside of this lambda isn't even using the lock. Is it? Am I missing an implicit piece of the construction here?

[leonMSFT]

I should probably change the name of the lock inside of the lambda, that's a good point.
As for whether the inside of the lambda is using the lock, we should technically be acquiring the lock before modifying finalVal since that's the shared resource right?

[miniksa]

I need an adult to answer that. I just copied this pattern from somewhere else. @lhecker halp.

[miniksa]

(This is where I stole the idea from:

terminal/src/cascadia/TerminalSettingsModel/CascadiaSettingsSerialization.cpp

Lines 57 to 78 in d57fb84

	template<typename TTask>
	static auto _extractValueFromTaskWithoutMainThreadAwait(TTask&& task) -> decltype(task.get())
	{
	using TVal = decltype(task.get());
	std::optional<TVal> finalVal{};
	std::condition_variable cv;
	std::mutex mtx;
	auto waitOnBackground = [&]() -> winrt::fire_and_forget {
	co_await winrt::resume_background();
	auto v{ co_await task };
	std::unique_lock<std::mutex> lock{ mtx };
	finalVal.emplace(std::move(v));
	cv.notify_all();
	};
	std::unique_lock<std::mutex> lock{ mtx };
	waitOnBackground();
	cv.wait(lock, [&]() { return finalVal.has_value(); });
	return *finalVal;
	}

)

[lhecker]

You can use til::latch for this now. Less overhead & easier to use. 🙂

• You need to import it yourself as <til/latch.h> (just like a stdlib header - no need to put it into pch.h)
• Instantiate it as til::latch latch(1);
• Replace the mutex/condition_variable code inside the lambda with lath.count_down()
• Replace the mutex/condition_variable code outside the lambda with latch.wait()
• Just make sure to write the data before counting down and only read from it after wait() has returned.

[ghost]

Hello @zadjii-msft!

Because this pull request has the AutoMerge label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

p.s. you can customize the way I help with merging this pull request, such as holding this pull request until a specific person approves. Simply @mention me (@msftbot) and give me an instruction to get started! Learn more here.

[ghost]

🎉Windows Terminal Preview v1.10.2383.0 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Store Download

[ghost]

🎉Windows Terminal Preview v1.11.2421.0 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Store Download