Crash using recursion inside a coroutine about swiftcoroutine HOT 3 CLOSED

@roisg Hi. It's not a bug, actually it's a stack buffer overflow.

This code will also crash:

func testRecursive() {
	let exp = expectation(description: "testRecursive")
	exp.expectedFulfillmentCount = 1
	DispatchQueue.global().async {
		try? self.recursiveFunction(count: 0)
		exp.fulfill()
	}
	wait(for: [exp], timeout: 3)
}

private func recursiveFunction(count: Int) throws {
	let _ = DispatchQueue.global().sync {
		"random_response"
	}
	print(count)
	if count < 10000 {
		try recursiveFunction(count: count + 1)
	}
}

The problem is that every thread has a stack with a limited size. For example, for background thread on iOS it is 256 kb. And when you call a function recursively, the thread stack fills up with stack frames. And if it reaches its limit, it will crash.
A coroutine also has a stack (I set it to 192 kb). That's why in recursive calls it will also crash, just like a thread when it reaches the limit.

I can only recommend not to use too many recursive calls. Neither inside coroutine nor outside coroutine.

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Thank you very much, @belozierov! You're absolutely right. This heavily recursive code was inherited by the usage of server-side Vapor's Futures, but now that it's possible, it's clear that re-working it to be iterative is the way to go.

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Would it be possible/desirable to specify a stack size for specific coroutines?

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