GetaddrinfoResolver succeeds futures on eventLoop (#3042)

### Motivation:

`testClientBindWorksOnSocketsBoundToEitherIPv4OrIPv6Only` would fail
sometimes leaking the IPv4 promise in `GetaddrinfoResolver`

`HappyEyeballsConnector` returns the connection when it resolves either
IPv4 of IPv6. It uses the `GetaddrinfoResolver` which holds a promise
for each of the IPv4 and IPv6 resolution; when one is completed the
connection will be returned and it is possible to start tearing down the
test and shutting down the event loop before the other is completed and
we leak the promise.

### Modifications:

Complete both futures on the event loop rather than the dispatch queue.

### Result:

The futures are completed in the same event loop tick meaning that we
cannot continue execution and leak one.

Benchmarks/Thresholds/5.10/NIOPosixBenchmarks.TCPEcho.p90.json

@@ -1,3 +1,3 @@
 {
-  "mallocCountTotal" : 555
+  "mallocCountTotal" : 107
 }

Benchmarks/Thresholds/5.9/NIOPosixBenchmarks.TCPEcho.p90.json

@@ -1,3 +1,3 @@
 {
-  "mallocCountTotal" : 556
+  "mallocCountTotal" : 109
 }

Benchmarks/Thresholds/6.0/NIOPosixBenchmarks.TCPEcho.p90.json

@@ -1,3 +1,3 @@
 {
-  "mallocCountTotal" : 548
+  "mallocCountTotal" : 107
 }

Benchmarks/Thresholds/nightly-6.0/NIOPosixBenchmarks.TCPEcho.p90.json

@@ -1,3 +1,3 @@
 {
-  "mallocCountTotal" : 548
+  "mallocCountTotal" : 107
 }

Benchmarks/Thresholds/nightly-main/NIOPosixBenchmarks.TCPEcho.p90.json

@@ -1,3 +1,3 @@
 {
-  "mallocCountTotal" : 548
+  "mallocCountTotal" : 107
 }

Sources/NIOPosix/Bootstrap.swift

@@ -956,8 +956,6 @@ public final class ClientBootstrap: NIOClientTCPBootstrapProtocol {
     ///
     /// Using `bind` is not necessary unless you need the local address to be bound to a specific address.
     ///
-    /// - Note: Using `bind` will disable Happy Eyeballs on this `Channel`.
-    ///
     /// - Parameters:
     ///   - address: The `SocketAddress` to bind on.
     public func bind(to address: SocketAddress) -> ClientBootstrap {
@@ -978,6 +976,8 @@ public final class ClientBootstrap: NIOClientTCPBootstrapProtocol {
 
     /// Specify the `host` and `port` to connect to for the TCP `Channel` that will be established.
     ///
+    /// - Note: Makes use of Happy Eyeballs.
+    ///
     /// - Parameters:
     ///   - host: The host to connect to.
     ///   - port: The port to connect to.

Sources/NIOPosix/GetaddrinfoResolver.swift

@@ -51,6 +51,7 @@ import struct WinSDK.SOCKADDR_IN6
 let offloadQueueTSV = ThreadSpecificVariable<DispatchQueue>()
 
 internal class GetaddrinfoResolver: Resolver {
+    private let loop: EventLoop
     private let v4Future: EventLoopPromise<[SocketAddress]>
     private let v6Future: EventLoopPromise<[SocketAddress]>
     private let aiSocktype: NIOBSDSocket.SocketType
@@ -67,6 +68,7 @@ internal class GetaddrinfoResolver: Resolver {
         aiSocktype: NIOBSDSocket.SocketType,
         aiProtocol: NIOBSDSocket.OptionLevel
     ) {
+        self.loop = loop
         self.v4Future = loop.makePromise()
         self.v6Future = loop.makePromise()
         self.aiSocktype = aiSocktype
@@ -90,7 +92,6 @@ internal class GetaddrinfoResolver: Resolver {
     /// Initiate a DNS AAAA query for a given host.
     ///
     /// Due to the nature of `getaddrinfo`, we only actually call the function once, in this function.
-    /// That means this function call actually blocks: sorry!
     ///
     /// - Parameters:
     ///   - host: The hostname to do an AAAA lookup on.
@@ -214,16 +215,24 @@ internal class GetaddrinfoResolver: Resolver {
             info = nextInfo
         }
 
-        v6Future.succeed(v6Results)
-        v4Future.succeed(v4Results)
+        // Ensure that both futures are succeeded in the same tick
+        // to avoid racing and potentially leaking a promise
+        self.loop.execute {
+            self.v6Future.succeed(v6Results)
+            self.v4Future.succeed(v4Results)
+        }
     }
 
     /// Record an error and fail the lookup process.
     ///
     /// - Parameters:
     ///   - error: The error encountered during lookup.
     private func fail(_ error: Error) {
-        self.v6Future.fail(error)
-        self.v4Future.fail(error)
+        // Ensure that both futures are succeeded in the same tick
+        // to avoid racing and potentially leaking a promise
+        self.loop.execute {
+            self.v6Future.fail(error)
+            self.v4Future.fail(error)
+        }
     }
 }

Tests/NIOPosixTests/BootstrapTest.swift

@@ -734,7 +734,7 @@ class BootstrapTest: XCTestCase {
             // Some platforms don't define "localhost" for IPv6, so check that
             // and use "ip6-localhost" instead.
             if !isIPv4 {
-                let hostResolver = GetaddrinfoResolver(loop: group.next(), aiSocktype: .stream, aiProtocol: .tcp)
+                let hostResolver = GetaddrinfoResolver(loop: self.group.next(), aiSocktype: .stream, aiProtocol: .tcp)
                 let hostv6 = try! hostResolver.initiateAAAAQuery(host: "localhost", port: 8088).wait()
                 if hostv6.isEmpty {
                     localhost = "ip6-localhost"
@@ -752,7 +752,7 @@ class BootstrapTest: XCTestCase {
                 XCTFail("can't connect channel 1")
                 return
             }
-            XCTAssertEqual(localIP, maybeChannel1?.localAddress?.ipAddress)
+            XCTAssertEqual(localIP, myChannel1Address.ipAddress)
             // Try 3: Bind the client to the same address/port as in try 2 but to server 2.
             XCTAssertNoThrow(
                 try ClientBootstrap(group: self.group)