add ipv6 only option for more predictable behavior

cgi.d

@@ -6030,6 +6030,8 @@ Socket startListening(string host, ushort port, ref bool tcp, ref void delegate(
 		}
 		cloexec(listener);
 		listener.setOption(SocketOptionLevel.SOCKET, SocketOption.REUSEADDR, true);
+		if(cast(Internet6Address) address)
+			listener.setOption(SocketOptionLevel.SOCKET, SocketOption.IPV6_V6ONLY, true);
 		listener.bind(address);
 		cleanup = delegate() {
 			listener.close();

core.d

@@ -61,7 +61,9 @@ version(Windows) {
 } else version(linux) {
 	version=Arsd_core_epoll;
 
-	version=Arsd_core_has_cloexec;
+	static if(__VERSION__ >= 2098) {
+		version=Arsd_core_has_cloexec;
+	}
 } else version(FreeBSD) {
 	version=Arsd_core_kqueue;
 
@@ -2561,6 +2563,8 @@ class AsyncFile : AbstractFile {
 	Reads or writes a file in one call. It might internally yield, but is generally blocking if it returns values. The callback ones depend on the implementation.
 
 	Tip: prefer the callback ones. If settings where async is possible, it will do async, and if not, it will sync.
+
+	NOT IMPLEMENTED
 +/
 void writeFile(string filename, const(void)[] contents) {
 
@@ -3123,6 +3127,9 @@ class AsyncSocket : AsyncFile {
 			setCloExec(handle);
 		}
 
+		int opt = 1;
+		setsockopt(handle, SOL_SOCKET, IPV6_V6ONLY, &opt, opt.sizeof);
+
 		// FIXME: chekc for broadcast
 
 		// FIXME: REUSEADDR ?
@@ -4316,11 +4323,158 @@ class AsyncReadResponse : AsyncOperationResponse {
 		runHelperFunction() - whomever it reports to is the parent
 +/
 
-/+
+class ScheduableTask : Fiber {
-class Task : Fiber {
+	private void delegate() dg;
 
+	// linked list stuff
+	private static ScheduableTask taskRoot;
+	private ScheduableTask previous;
+	private ScheduableTask next;
+
+	// need the controlling thread to know how to wake it up if it receives a message
+	private Thread controllingThread;
+
+	// the api
+
+	this(void delegate() dg) {
+		assert(dg !is null);
+
+		this.dg = dg;
+		super(&taskRunner);
+
+		if(taskRoot !is null) {
+			this.next = taskRoot;
+			taskRoot.previous = this;
+		}
+		taskRoot = this;
+	}
+
+	/+
+	enum BehaviorOnCtrlC {
+		ignore,
+		cancel,
+		deliverMessage
+	}
+	+/
+
+	private bool cancelled;
+
+	public void cancel() {
+		this.cancelled = true;
+		// if this is running, we can throw immediately
+		// otherwise if we're calling from an appropriate thread, we can call it immediately
+		// otherwise we need to queue a wakeup to its own thread.
+		// tbh we should prolly just queue it every time
+	}
+
+	private void taskRunner() {
+		try {
+			dg();
+		} catch(TaskCancelledException tce) {
+			// this space intentionally left blank;
+			// the purpose of this exception is to just
+			// let the fiber's destructors run before we
+			// let it die.
+		} catch(Throwable t) {
+			if(taskUncaughtException is null) {
+				throw t;
+			} else {
+				taskUncaughtException(t);
+			}
+		} finally {
+			if(this is taskRoot) {
+				taskRoot = taskRoot.next;
+				if(taskRoot !is null)
+					taskRoot.previous = null;
+			} else {
+				assert(this.previous !is null);
+				assert(this.previous.next is this);
+				this.previous.next = this.next;
+				if(this.next !is null)
+					this.next.previous = this.previous;
+			}
+		}
+	}
 }
+
+/++
+
 +/
+void delegate(Throwable t) taskUncaughtException;
+
+/++
+	Gets an object that lets you control a schedulable task (which is a specialization of a fiber) and can be used in an `if` statement.
+
+	---
+		if(auto controller = inSchedulableTask()) {
+			controller.yieldUntilReadable(...);
+		}
+	---
+
+	History:
+		Added August 11, 2023 (dub v11.1)
++/
+SchedulableTaskController inSchedulableTask() {
+	import core.thread.fiber;
+
+	if(auto fiber = Fiber.getThis) {
+		return SchedulableTaskController(cast(ScheduableTask) fiber);
+	}
+
+	return SchedulableTaskController(null);
+}
+
+/// ditto
+struct SchedulableTaskController {
+	private this(ScheduableTask fiber) {
+		this.fiber = fiber;
+	}
+
+	private ScheduableTask fiber;
+
+	/++
+
+	+/
+	bool opCast(T : bool)() {
+		return fiber !is null;
+	}
+
+	/++
+
+	+/
+	version(Posix)
+	void yieldUntilReadable(NativeFileHandle handle) {
+		assert(fiber !is null);
+
+		auto cb = new CallbackHelper(() { fiber.call(); });
+
+		// FIXME: if the fd is already registered in this thread it can throw...
+		version(Windows)
+			auto rearmToken = getThisThreadEventLoop().addCallbackOnFdReadableOneShot(handle, cb);
+		else
+			auto rearmToken = getThisThreadEventLoop().addCallbackOnFdReadableOneShot(handle, cb);
+
+		// FIXME: this is only valid if the fiber is only ever going to run in this thread!
+		fiber.yield();
+
+		rearmToken.unregister();
+
+		// what if there are other messages, like a ctrl+c?
+		if(fiber.cancelled)
+			throw new TaskCancelledException();
+	}
+
+	version(Windows)
+	void yieldUntilSignaled(NativeFileHandle handle) {
+		// add it to the WaitForMultipleObjects thing w/ a cb
+	}
+}
+
+class TaskCancelledException : object.Exception {
+	this() {
+		super("Task cancelled");
+	}
+}
 
 private class CoreWorkerThread : Thread {
 	this(EventLoopType type) {
@@ -4338,7 +4492,13 @@ private class CoreWorkerThread : Thread {
 			atomicOp!"-="(runningCount, 1);
 		}
 
-		eventLoop.run(() => true);
+		eventLoop.run(() => cancelled);
+	}
+
+	private bool cancelled;
+
+	void cancel() {
+		cancelled = true;
 	}
 
 	EventLoopType type;
@@ -4381,6 +4541,14 @@ private class CoreWorkerThread : Thread {
 				started = true;
 			}
 		}
+
+		void cancelAll() {
+			foreach(runner; taskRunners)
+				runner.cancel();
+			foreach(runner; helperRunners)
+				runner.cancel();
+
+		}
 	}
 }
 
@@ -4406,6 +4574,7 @@ private int numberOfCpus() {
 
 	Its destructor runs the event loop then waits to for the workers to finish to clean them up.
 +/
+// FIXME: single instance?
 struct ArsdCoreApplication {
 	private ICoreEventLoop impl;
 
@@ -4436,21 +4605,25 @@ struct ArsdCoreApplication {
 	@disable new();
 
 	~this() {
-		run();
+		if(!alreadyRun)
+			run();
 		exitApplication();
 		waitForWorkersToExit(3000);
 	}
 
 	void exitApplication() {
-
+		CoreWorkerThread.cancelAll();
 	}
 
 	void waitForWorkersToExit(int timeoutMilliseconds) {
 
 	}
 
+	private bool alreadyRun;
+
 	void run() {
-		impl.run(() => true);
+		impl.run(() => false);
+		alreadyRun = true;
 	}
 }