From 23901dcaadf5bd916122e41bb7724d4c3dd4e9e1 Mon Sep 17 00:00:00 2001
From: Billy O'Neal <billy.oneal@gmail.com>
Date: Tue, 26 Mar 2019 20:49:43 -0700
Subject: [PATCH] Fix data race, GitHub #1085 (#1088)

* Fix data race, GitHub #1085

* Fix *nix typos.
---
 Release/src/pplx/pplx.cpp | 59 +++++++++++++++++----------------------
 1 file changed, 26 insertions(+), 33 deletions(-)

diff --git a/Release/src/pplx/pplx.cpp b/Release/src/pplx/pplx.cpp
index 5f9626edd8..618c02b908 100644
--- a/Release/src/pplx/pplx.cpp
+++ b/Release/src/pplx/pplx.cpp
@@ -14,13 +14,8 @@
 #include "stdafx.h"
 
 #if !defined(_WIN32) || CPPREST_FORCE_PPLX
-
 #include "pplx/pplx.h"
-
-// Disable false alarm code analyze warning
-#if defined(_MSC_VER)
-#pragma warning(disable : 26165 26110)
-#endif
+#include <atomic>
 
 namespace pplx
 {
@@ -36,24 +31,16 @@ class _Spin_lock
 
     void lock()
     {
-        if (details::atomic_compare_exchange(_M_lock, 1l, 0l) != 0l)
+        while (_M_lock.test_and_set())
         {
-            do
-            {
-                pplx::details::platform::YieldExecution();
-
-            } while (details::atomic_compare_exchange(_M_lock, 1l, 0l) != 0l);
+            pplx::details::platform::YieldExecution();
         }
     }
 
-    void unlock()
-    {
-        // fence for release semantics
-        details::atomic_exchange(_M_lock, 0l);
-    }
+    void unlock() { _M_lock.clear(); }
 
 private:
-    atomic_long _M_lock;
+    std::atomic_flag _M_lock;
 };
 
 typedef ::pplx::scoped_lock<_Spin_lock> _Scoped_spin_lock;
@@ -63,44 +50,49 @@ static struct _pplx_g_sched_t
 {
     typedef std::shared_ptr<pplx::scheduler_interface> sched_ptr;
 
-    _pplx_g_sched_t() { m_state = post_ctor; }
+    _pplx_g_sched_t() { m_state.store(post_ctor, std::memory_order_relaxed); }
 
-    ~_pplx_g_sched_t() { m_state = post_dtor; }
+    ~_pplx_g_sched_t() { m_state.store(post_dtor, std::memory_order_relaxed); }
 
     sched_ptr get_scheduler()
     {
-        switch (m_state)
+        sched_ptr result;
+        switch (m_state.load(std::memory_order_relaxed))
         {
             case post_ctor:
                 // This is the 99.9% case.
-
-                if (!m_scheduler)
                 {
                     ::pplx::details::_Scoped_spin_lock lock(m_spinlock);
                     if (!m_scheduler)
                     {
                         m_scheduler = std::make_shared<::pplx::default_scheduler_t>();
                     }
-                }
 
-                return m_scheduler;
+                    result = m_scheduler;
+                } // unlock
+
+                break;
             default:
                 // This case means the global m_scheduler is not available.
                 // We spin off an individual scheduler instead.
-                return std::make_shared<::pplx::default_scheduler_t>();
+                result = std::make_shared<::pplx::default_scheduler_t>();
+                break;
         }
+
+        return result;
     }
 
     void set_scheduler(sched_ptr scheduler)
     {
-        if (m_state == pre_ctor || m_state == post_dtor)
+        const auto localState = m_state.load(std::memory_order_relaxed);
+        if (localState == pre_ctor || localState == post_dtor)
         {
             throw invalid_operation("Scheduler cannot be initialized now");
         }
 
         ::pplx::details::_Scoped_spin_lock lock(m_spinlock);
 
-        if (m_scheduler != nullptr)
+        if (m_scheduler)
         {
             throw invalid_operation("Scheduler is already initialized");
         }
@@ -108,14 +100,15 @@ static struct _pplx_g_sched_t
         m_scheduler = std::move(scheduler);
     }
 
-    enum
+    enum m_state_values
     {
-        pre_ctor = 0,
-        post_ctor = 1,
-        post_dtor = 2
-    } m_state;
+        pre_ctor,
+        post_ctor,
+        post_dtor
+    };
 
 private:
+    std::atomic<m_state_values> m_state;
     pplx::details::_Spin_lock m_spinlock;
     sched_ptr m_scheduler;
 } _pplx_g_sched;