Add mechanism for disabling automatic Winsock initialisation.

asio/include/asio/detail/impl/winsock_init.ipp

diff --git a/asio/include/asio/detail/impl/winsock_init.ipp b/asio/include/asio/detail/impl/winsock_init.ipp
index ca4c3fc..b5dec69 100644
--- a/asio/include/asio/detail/impl/winsock_init.ipp
+++ b/asio/include/asio/detail/impl/winsock_init.ipp
@@ -40,6 +40,14 @@
   }
 }
 
+void winsock_init_base::manual_startup(data& d)
+{
+  if (::InterlockedIncrement(&d.init_count_) == 1)
+  {
+    ::InterlockedExchange(&d.result_, 0);
+  }
+}
+
 void winsock_init_base::cleanup(data& d)
 {
   if (::InterlockedDecrement(&d.init_count_) == 0)
@@ -48,6 +56,11 @@
   }
 }
 
+void winsock_init_base::manual_cleanup(data& d)
+{
+  ::InterlockedDecrement(&d.init_count_);
+}
+
 void winsock_init_base::throw_on_error(data& d)
 {
   long result = ::InterlockedExchangeAdd(&d.result_, 0);

asio/include/asio/detail/winsock_init.hpp

diff --git a/asio/include/asio/detail/winsock_init.hpp b/asio/include/asio/detail/winsock_init.hpp
index 404f5d1..0420ce7 100644
--- a/asio/include/asio/detail/winsock_init.hpp
+++ b/asio/include/asio/detail/winsock_init.hpp
@@ -38,8 +38,12 @@
   ASIO_DECL static void startup(data& d,
       unsigned char major, unsigned char minor);
 
+  ASIO_DECL static void manual_startup(data& d);
+
   ASIO_DECL static void cleanup(data& d);
 
+  ASIO_DECL static void manual_cleanup(data& d);
+
   ASIO_DECL static void throw_on_error(data& d);
 };
 
@@ -65,7 +69,41 @@
     cleanup(data_);
   }
 
+  // This class may be used to indicate that user code will manage Winsock
+  // initialisation and cleanup. This may be required in the case of a DLL, for
+  // example, where it is not safe to initialise Winsock from global object
+  // constructors.
+  //
+  // To prevent asio from initialising Winsock, the object must be constructed
+  // before any Asio's own global objects. With MSVC, this may be accomplished
+  // by adding the following code to the DLL:
+  //
+  //   #pragma warning(push)
+  //   #pragma warning(disable:4073)
+  //   #pragma init_seg(lib)
+  //   asio::detail::winsock_init<>::manual manual_winsock_init;
+  //   #pragma warning(pop)
+  class manual
+  {
+  public:
+    manual()
+    {
+      manual_startup(data_);
+    }
+
+    manual(const manual&)
+    {
+      manual_startup(data_);
+    }
+
+    ~manual()
+    {
+      manual_cleanup(data_);
+    }
+  };
+
 private:
+  friend class manual;
   static data data_;
 };