Factor shared threadpool setup/teardown behavior out of platform depe…

…ndent policies.

Release/src/pplx/threadpool.cpp

@@ -10,7 +10,9 @@
 #include "pplx/threadpool.h"
 
 #include <boost/asio/detail/thread.hpp>
+#include <new>
 #include <vector>
+#include <type_traits>
 
 #if defined(__ANDROID__)
 #include <android/log.h>
@@ -19,6 +21,32 @@
 
 namespace
 {
+#if defined(__ANDROID__)
+// This pointer will be 0-initialized by default (at load time).
+std::atomic<JavaVM*> JVM;
+
+JNIEnv* get_jvm_env()
+{
+    abort_if_no_jvm();
+    JNIEnv* env = nullptr;
+    auto result = JVM.load()->AttachCurrentThread(&env, nullptr);
+    if (result != JNI_OK)
+    {
+        throw std::runtime_error("Could not attach to JVM");
+    }
+
+    return env;
+}
+
+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");
+        std::abort();
+    }
+}
+#endif // __ANDROID__
 
 struct threadpool_impl final : crossplat::threadpool
 {
@@ -39,6 +67,11 @@ struct threadpool_impl final : crossplat::threadpool
         }
     }
 
+    threadpool_impl& get_shared()
+    {
+        return *this;
+    }
+
 private:
     void add_thread()
     {
@@ -50,103 +83,70 @@ struct threadpool_impl final : crossplat::threadpool
     {
         crossplat::JVM.load()->DetachCurrentThread();
     }
-#endif
+#endif // __ANDROID__
 
     static void* thread_start(void *arg) CPPREST_NOEXCEPT
     {
 #if defined(__ANDROID__)
         // Calling get_jvm_env() here forces the thread to be attached.
         crossplat::get_jvm_env();
         pthread_cleanup_push(detach_from_java, nullptr);
-#endif
+#endif // __ANDROID__
         threadpool_impl* _this = reinterpret_cast<threadpool_impl*>(arg);
         _this->m_service.run();
 #if defined(__ANDROID__)
         pthread_cleanup_pop(true);
-#endif
+#endif // __ANDROID__
         return arg;
     }
 
     std::vector<std::unique_ptr<boost::asio::detail::thread>> m_threads;
     boost::asio::io_service::work m_work;
 };
-}
 
-namespace crossplat
+#if defined(_WIN32)
+struct shared_threadpool
 {
-#if defined(__ANDROID__)
-// This pointer will be 0-initialized by default (at load time).
-std::atomic<JavaVM*> JVM;
+    typename std::aligned_union<0, threadpool_impl>::type shared_storage;
 
-static void abort_if_no_jvm()
-{
-    if (JVM == nullptr)
+    threadpool_impl& get_shared()
     {
-        __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();
+        return reinterpret_cast<threadpool_impl&>(shared_storage);
     }
-}
 
-JNIEnv* get_jvm_env()
-{
-    abort_if_no_jvm();
-    JNIEnv* env = nullptr;
-    auto result = JVM.load()->AttachCurrentThread(&env, nullptr);
-    if (result != JNI_OK)
+    shared_threadpool(size_t n)
     {
-        throw std::runtime_error("Could not attach to JVM");
+        ::new (static_cast<void*>(&get_shared())) threadpool_impl(n);
     }
-
-    return env;
-}
-
-threadpool& threadpool::shared_instance()
-{
-    abort_if_no_jvm();
-    static threadpool_impl s_shared(40);
-    return s_shared;
-}
-
-#elif defined(_WIN32)
-
-// if linked into a DLL, the threadpool shared instance will be destroyed at DLL_PROCESS_DETACH,
-// at which stage joining threads causes deadlock, hence this dance
-threadpool& threadpool::shared_instance()
-{
-    static bool terminate_threads = false;
-    static struct restore_terminate_threads
+    ~shared_threadpool()
     {
-        ~restore_terminate_threads()
-        {
-            boost::asio::detail::thread::set_terminate_threads(terminate_threads);
-        }
-    } destroyed_after;
-
-    static threadpool_impl s_shared(40);
+        // if linked into a DLL, the threadpool shared instance will be
+        // destroyed at DLL_PROCESS_DETACH, at which stage joining threads
+        // causes deadlock, hence this dance
+        bool terminate_threads = boost::asio::detail::thread::terminate_threads();
+        boost::asio::detail::thread::set_terminate_threads(true);
+        get_shared().~threadpool_impl();
+        boost::asio::detail::thread::set_terminate_threads(terminate_threads);
+    }
+};
 
-    static struct enforce_terminate_threads
-    {
-        ~enforce_terminate_threads()
-        {
-            terminate_threads = boost::asio::detail::thread::terminate_threads();
-            boost::asio::detail::thread::set_terminate_threads(true);
-        }
-    } destroyed_before;
+typedef shared_threadpool platform_shared_threadpool;
+#else // ^^^ _WIN32 ^^^ // vvv !_WIN32 vvv //
+typedef threadpool_impl platform_shared_threadpool;
+#endif
 
-    return s_shared;
 }
 
-#else
-
-// initialize the static shared threadpool
+namespace crossplat
+{
 threadpool& threadpool::shared_instance()
 {
-    static threadpool_impl s_shared(40);
-    return s_shared;
+#if defined(__ANDROID__)
+    abort_if_no_jvm();
+#endif // __ANDROID__
+    static platform_shared_threadpool s_shared_impl(40);
+    return s_shared_impl.get_shared();
 }
-
-#endif
-
 }
 
 #if defined(__ANDROID__)
@@ -159,4 +159,4 @@ std::unique_ptr<crossplat::threadpool> crossplat::threadpool::construct(size_t n
 {
     return std::unique_ptr<crossplat::threadpool>(new threadpool_impl(num_threads));
 }
-#endif
+#endif //  !defined(CPPREST_EXCLUDE_WEBSOCKETS) || !defined(_WIN32)