From bac9f5f1fa8b79cd2b1fd2db624f0609080c503e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20Wei=C3=9F?= <johannesweiss@apple.com>
Date: Thu, 24 Aug 2017 11:08:05 +0100
Subject: [PATCH] Revert "Fix for a race condition in URLSession (#949)"

This reverts commit 015ded4d70a7cf4b2741d7206fc60a3d1ceffe03.
---
 Foundation/URLSession/http/MultiHandle.swift | 56 +++++++-------------
 1 file changed, 19 insertions(+), 37 deletions(-)

diff --git a/Foundation/URLSession/http/MultiHandle.swift b/Foundation/URLSession/http/MultiHandle.swift
index bb2acafda6..506c9a9f23 100644
--- a/Foundation/URLSession/http/MultiHandle.swift
+++ b/Foundation/URLSession/http/MultiHandle.swift
@@ -39,11 +39,7 @@ extension URLSession {
         let group = DispatchGroup()
         fileprivate var easyHandles: [_EasyHandle] = []
         fileprivate var timeoutSource: _TimeoutSource? = nil
-
-        //SR-4567: we need to synchronize the register/unregister commands to the epoll machinery in libdispatch
-        fileprivate let commandQueue: DispatchQueue = DispatchQueue(label: "Register-unregister synchronization")
-        fileprivate var cancelInProgress: DispatchSemaphore? = nil
-
+        
         init(configuration: URLSession._Configuration, workQueue: DispatchQueue) {
             queue = DispatchQueue(label: "MultiHandle.isolation", target: workQueue)
             setupCallbacks()
@@ -103,33 +99,25 @@ fileprivate extension URLSession._MultiHandle {
         // through libdispatch (DispatchSource) and store the source(s) inside
         // a `SocketSources` which we in turn store inside libcurl's multi handle
         // by means of curl_multi_assign() -- we retain the object fist.
-        commandQueue.async {
-            self.cancelInProgress?.wait()
-            self.cancelInProgress = nil
-
-            let action = _SocketRegisterAction(rawValue: CFURLSessionPoll(value: what))
-            var socketSources = _SocketSources.from(socketSourcePtr: socketSourcePtr)
-            if socketSources == nil && action.needsSource {
-                let s = _SocketSources()
-                let p = Unmanaged.passRetained(s).toOpaque()
-                CFURLSessionMultiHandleAssign(self.rawHandle, socket, UnsafeMutableRawPointer(p))
-                socketSources = s
-            } else if socketSources != nil && action == .unregister {
-                //the beginning of an unregister operation
-                self.cancelInProgress = DispatchSemaphore(value: 0)
-                // We need to release the stored pointer:
-                if let opaque = socketSourcePtr {
-                    Unmanaged<_SocketSources>.fromOpaque(opaque).release()
-                }
-                socketSources?.tearDown(self.cancelInProgress)
-                socketSources = nil
+        let action = _SocketRegisterAction(rawValue: CFURLSessionPoll(value: what))
+        var socketSources = _SocketSources.from(socketSourcePtr: socketSourcePtr)
+        if socketSources == nil && action.needsSource {
+            let s = _SocketSources()
+            let p = Unmanaged.passRetained(s).toOpaque()
+            CFURLSessionMultiHandleAssign(rawHandle, socket, UnsafeMutableRawPointer(p))
+            socketSources = s
+        } else if socketSources != nil && action == .unregister {
+            // We need to release the stored pointer:
+            if let opaque = socketSourcePtr {
+                Unmanaged<_SocketSources>.fromOpaque(opaque).release()
             }
-            if let ss = socketSources {
-                let handler = DispatchWorkItem { [weak self] in
-                    self?.performAction(for: socket)
-                }
-                ss.createSources(with: action, fileDescriptor: Int(socket), queue: self.queue, handler: handler)
+            socketSources = nil
+        }
+        if let ss = socketSources {
+            let handler = DispatchWorkItem { [weak self] in
+                self?.performAction(for: socket)
             }
+            ss.createSources(with: action, fileDescriptor: Int(socket), queue: queue, handler: handler)
         }
         return 0
     }
@@ -411,18 +399,12 @@ fileprivate class _SocketSources {
         s.resume()
     }
 
-    func tearDown(_ cancelInProgress: DispatchSemaphore?) {
-        let cancelHandler = DispatchWorkItem {
-            //the real end of an unregister operation!
-            cancelInProgress?.signal()
-        }
+    func tearDown() {
         if let s = readSource {
-            s.setCancelHandler(handler: cancelHandler)
             s.cancel()
         }
         readSource = nil
         if let s = writeSource {
-            s.setCancelHandler(handler: cancelHandler)
             s.cancel()
         }
         writeSource = nil