Support preconditionInEventLoop. (#11)

Motivation:

In SwiftNIO 1.11 we shipped improved interfaces for Channels to support
asserting being in the event loop. This is necessary because Dispatch
provides no non-precondition way to 100% guarantee that you are on a
specific queue, which is a requirement for accurate behaviour of
inEventLoop.

Modifications:

- Added an implementation of preconditionInEventLoop.
- Changed all assertions to use new interface.
- Required NIO 1.11.

Result:

Accurate assertions

Package.swift

@@ -23,7 +23,7 @@ let package = Package(
         .executable(name: "NIOTSHTTPServer", targets: ["NIOTSHTTPServer"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-nio.git", from: "1.8.0"),
+        .package(url: "https://github.com/apple/swift-nio.git", from: "1.11.0"),
     ],
     targets: [
         .target(name: "NIOTransportServices",

Sources/NIOTransportServices/NIOTSConnectionChannel.swift

@@ -276,7 +276,7 @@ extension NIOTSConnectionChannel: Channel {
     }
 
     private func setOption0<T: ChannelOption>(option: T, value: T.OptionType) throws {
-        assert(eventLoop.inEventLoop)
+        self.eventLoop.assertInEventLoop()
 
         guard !self.closed else {
             throw ChannelError.ioOnClosedChannel
@@ -320,7 +320,7 @@ extension NIOTSConnectionChannel: Channel {
     }
 
     func getOption0<T: ChannelOption>(option: T) throws -> T.OptionType {
-        assert(eventLoop.inEventLoop)
+        self.eventLoop.assertInEventLoop()
 
         guard !self.closed else {
             throw ChannelError.ioOnClosedChannel

Sources/NIOTransportServices/NIOTSEventLoop.swift

@@ -71,6 +71,12 @@ internal class NIOTSEventLoop: QoSEventLoop {
         return self.state == .active
     }
 
+    /// Returns whether the currently executing code is on the event loop.
+    ///
+    /// Due to limitations in Dispatch's API, this check is pessimistic: there are circumstances where a perfect
+    /// implementation *could* return `true`, but this version will be unable to prove that and will return `false`.
+    /// If you need to write an assertion about being in the event loop that must be correct, use SwiftNIO 1.11 or
+    /// later and call `preconditionInEventLoop` and `assertInEventLoop`.
     public var inEventLoop: Bool {
         return DispatchQueue.getSpecific(key: self.inQueueKey) == self.loopID
     }
@@ -127,6 +133,10 @@ internal class NIOTSEventLoop: QoSEventLoop {
             queue.async { callback(error) }
         }
     }
+
+    func preconditionInEventLoop(file: StaticString, line: UInt) {
+        dispatchPrecondition(condition: .onQueue(self.loop))
+    }
 }
 
 extension NIOTSEventLoop {

Sources/NIOTransportServices/NIOTSListenerBootstrap.swift

@@ -276,16 +276,16 @@ private class AcceptHandler: ChannelInboundHandler {
         @inline(__always)
         func setupChildChannel() -> EventLoopFuture<Void> {
             return self.childChannelOptions.applyAll(channel: newChannel).then { () -> EventLoopFuture<Void> in
-                assert(childLoop.inEventLoop)
+                childLoop.assertInEventLoop()
                 return childInitializer(newChannel)
             }
         }
 
         @inline(__always)
         func fireThroughPipeline(_ future: EventLoopFuture<Void>) {
-            assert(ctxEventLoop.inEventLoop)
+            ctxEventLoop.assertInEventLoop()
             future.then { (_) -> EventLoopFuture<Void> in
-                assert(ctxEventLoop.inEventLoop)
+                ctxEventLoop.assertInEventLoop()
                 guard ctx.channel.isActive else {
                     return newChannel.close().thenThrowing {
                         throw ChannelError.ioOnClosedChannel
@@ -294,7 +294,7 @@ private class AcceptHandler: ChannelInboundHandler {
                 ctx.fireChannelRead(self.wrapInboundOut(newChannel))
                 return ctx.eventLoop.newSucceededFuture(result: ())
             }.whenFailure { error in
-                assert(ctx.eventLoop.inEventLoop)
+                ctx.eventLoop.assertInEventLoop()
                 _ = newChannel.close()
                 ctx.fireErrorCaught(error)
             }

Sources/NIOTransportServices/NIOTSListenerChannel.swift

@@ -139,7 +139,7 @@ extension NIOTSListenerChannel: Channel {
     }
 
     private func setOption0<T: ChannelOption>(option: T, value: T.OptionType) throws {
-        assert(eventLoop.inEventLoop)
+        self.eventLoop.assertInEventLoop()
 
         guard !self.closed else {
             throw ChannelError.ioOnClosedChannel
@@ -178,7 +178,7 @@ extension NIOTSListenerChannel: Channel {
     }
 
     func getOption0<T: ChannelOption>(option: T) throws -> T.OptionType {
-        assert(eventLoop.inEventLoop)
+        self.eventLoop.assertInEventLoop()
 
         guard !self.closed else {
             throw ChannelError.ioOnClosedChannel