Remove use of aligned_union that broke CentOS 7. (microsoft#987)

Author: BillyONeal

Release/src/pplx/threadpool.cpp

@@ -1,18 +1,17 @@
 /***
-* Copyright (C) Microsoft. All rights reserved.
-* Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
-*
-* =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
-**/
+ * Copyright (C) Microsoft. All rights reserved.
+ * Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
+ **/
 #include "stdafx.h"
 
 #if !defined(CPPREST_EXCLUDE_WEBSOCKETS) || !defined(_WIN32)
 #include "pplx/threadpool.h"
 
 #include <boost/asio/detail/thread.hpp>
 #include <new>
-#include <vector>
 #include <type_traits>
+#include <utility>
+#include <vector>
 
 #if defined(__ANDROID__)
 #include <android/log.h>
@@ -29,9 +28,11 @@ static void abort_if_no_jvm()
 {
     if (JVM == nullptr)
     {
-        __android_log_print(ANDROID_LOG_ERROR, "CPPRESTSDK", "%s",
-            "The CppREST SDK must be initialized before first use on android: "
-            "https://github.com/Microsoft/cpprestsdk/wiki/How-to-build-for-Android");
+        __android_log_print(ANDROID_LOG_ERROR,
+                            "CPPRESTSDK",
+                            "%s",
+                            "The CppREST SDK must be initialized before first use on android: "
+                            "https://github.com/Microsoft/cpprestsdk/wiki/How-to-build-for-Android");
         std::abort();
     }
 }
@@ -52,9 +53,7 @@ JNIEnv* get_jvm_env()
 
 struct threadpool_impl final : crossplat::threadpool
 {
-    threadpool_impl(size_t n)
-        : crossplat::threadpool(n)
-        , m_work(m_service)
+    threadpool_impl(size_t n) : crossplat::threadpool(n), m_work(m_service)
     {
         for (size_t i = 0; i < n; i++)
             add_thread();
@@ -69,26 +68,20 @@ struct threadpool_impl final : crossplat::threadpool
         }
     }
 
-    threadpool_impl& get_shared()
-    {
-        return *this;
-    }
+    threadpool_impl& get_shared() { return *this; }
 
 private:
     void add_thread()
     {
-        m_threads.push_back(std::unique_ptr<boost::asio::detail::thread>(
-            new boost::asio::detail::thread([&]{ thread_start(this); })));
+        m_threads.push_back(
+            std::unique_ptr<boost::asio::detail::thread>(new boost::asio::detail::thread([&] { thread_start(this); })));
     }
 
 #if defined(__ANDROID__)
-    static void detach_from_java(void*)
-    {
-        JVM.load()->DetachCurrentThread();
-    }
+    static void detach_from_java(void*) { JVM.load()->DetachCurrentThread(); }
 #endif // __ANDROID__
 
-    static void* thread_start(void *arg) CPPREST_NOEXCEPT
+    static void* thread_start(void* arg) CPPREST_NOEXCEPT
     {
 #if defined(__ANDROID__)
         // Calling get_jvm_env() here forces the thread to be attached.
@@ -110,17 +103,14 @@ struct threadpool_impl final : crossplat::threadpool
 #if defined(_WIN32)
 struct shared_threadpool
 {
-    std::aligned_union<0, threadpool_impl>::type shared_storage;
+    union {
+        threadpool_impl shared_storage;
+    };
 
-    threadpool_impl& get_shared()
-    {
-        return reinterpret_cast<threadpool_impl&>(shared_storage);
-    }
+    threadpool_impl& get_shared() { return shared_storage; }
+
+    shared_threadpool(size_t n) : shared_storage(n) {}
 
-    shared_threadpool(size_t n)
-    {
-        ::new (static_cast<void*>(&get_shared())) threadpool_impl(n);
-    }
     ~shared_threadpool()
     {
         // if linked into a DLL, the threadpool shared instance will be
@@ -138,52 +128,59 @@ typedef shared_threadpool platform_shared_threadpool;
 typedef threadpool_impl platform_shared_threadpool;
 #endif
 
-std::pair<bool, platform_shared_threadpool*> initialize_shared_threadpool(size_t num_threads)
+namespace
 {
-    static std::aligned_union<0, platform_shared_threadpool>::type storage;
-    platform_shared_threadpool* const ptr =
-        &reinterpret_cast<platform_shared_threadpool&>(storage);
-    bool initialized_this_time = false;
-#if defined(__ANDROID__)
-    // mutex based implementation due to paranoia about (lack of) call_once support on Android
-    // remove this if/when call_once is supported
-    static std::mutex mtx;
-    static std::atomic<bool> initialized;
-    abort_if_no_jvm();
-    if (!initialized.load())
+template<class T>
+struct uninitialized
+{
+    union {
+        T storage;
+    };
+
+    bool initialized;
+
+    uninitialized() CPPREST_NOEXCEPT : initialized(false) {}
+    uninitialized(const uninitialized&) = delete;
+    uninitialized& operator=(const uninitialized&) = delete;
+    ~uninitialized()
     {
-        std::lock_guard<std::mutex> guard(mtx);
-        if (!initialized.load())
+        if (initialized)
         {
-            ::new (static_cast<void*>(ptr)) platform_shared_threadpool(num_threads);
-            initialized.store(true);
-            initialized_this_time = true;
+            storage.~T();
         }
-    }   // also unlock
+    }
+
+    template<class... Args>
+    void construct(Args&&... vals)
+    {
+        ::new (static_cast<void*>(&storage)) T(std::forward<Args>(vals)...);
+        initialized = true;
+    }
+};
+} // unnamed namespace
 
-#else // ^^^ __ANDROID__ ^^^ // vvv !__ANDROID___ vvv //
+std::pair<bool, platform_shared_threadpool*> initialize_shared_threadpool(size_t num_threads)
+{
+    static uninitialized<platform_shared_threadpool> uninit_threadpool;
+    bool initialized_this_time = false;
     static std::once_flag of;
 
-// #if defined(__ANDROID__) // if call_once can be used for android
-//     abort_if_no_jvm();
-// #endif // __ANDROID__
-    std::call_once(of, [num_threads, ptr, &initialized_this_time] {
-        ::new (static_cast<void*>(ptr)) platform_shared_threadpool(num_threads);
+    #if defined(__ANDROID__)
+        abort_if_no_jvm();
+    #endif // __ANDROID__
+
+    std::call_once(of, [num_threads, &initialized_this_time] {
+        uninit_threadpool.construct(num_threads);
         initialized_this_time = true;
     });
-#endif // __ANDROID__
 
-    return {initialized_this_time, ptr};
+    return {initialized_this_time, &uninit_threadpool.storage};
 }
 }
 
 namespace crossplat
 {
-threadpool& threadpool::shared_instance()
-{
-    return initialize_shared_threadpool(40).second->get_shared();
-}
-
+threadpool& threadpool::shared_instance() { return initialize_shared_threadpool(40).second->get_shared(); }
 
 void threadpool::initialize_with_threads(size_t num_threads)
 {
@@ -196,9 +193,7 @@ void threadpool::initialize_with_threads(size_t num_threads)
 }
 
 #if defined(__ANDROID__)
-void cpprest_init(JavaVM* vm) {
-    JVM = vm;
-}
+void cpprest_init(JavaVM* vm) { JVM = vm; }
 #endif
 
 std::unique_ptr<crossplat::threadpool> crossplat::threadpool::construct(size_t num_threads)