From 5c402fd62c073335c279686a62d77191682e9b79 Mon Sep 17 00:00:00 2001
From: David McFarland <corngood@gmail.com>
Date: Wed, 17 Dec 2025 12:53:27 -0400
Subject: [PATCH] Fix cygwin build.

---
 include/boost/asio/detail/config.hpp          | 29 +++----
 include/boost/asio/detail/fd_set_adapter.hpp  |  2 +-
 include/boost/asio/detail/hash_map.hpp        |  4 +-
 include/boost/asio/detail/impl/null_event.ipp |  6 +-
 include/boost/asio/detail/impl/socket_ops.ipp | 84 +++++++++----------
 .../asio/detail/posix_fd_set_adapter.hpp      |  1 -
 include/boost/asio/detail/select_reactor.hpp  |  2 +-
 include/boost/asio/detail/socket_ops.hpp      |  2 +-
 include/boost/asio/detail/socket_types.hpp    |  4 +-
 .../boost/asio/detail/win_fd_set_adapter.hpp  |  2 +-
 include/boost/asio/error.hpp                  |  9 +-
 include/boost/asio/impl/error.ipp             |  2 +-
 include/boost/asio/io_context.hpp             |  4 +-
 13 files changed, 67 insertions(+), 84 deletions(-)

diff --git a/include/boost/asio/detail/config.hpp b/include/boost/asio/detail/config.hpp
index 342d20fb4..fc77bb24b 100644
--- a/include/boost/asio/detail/config.hpp
+++ b/include/boost/asio/detail/config.hpp
@@ -720,7 +720,7 @@
 #endif // !defined(BOOST_ASIO_WINDOWS)
 
 // Windows: target OS version.
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # if !defined(_WIN32_WINNT) && !defined(_WIN32_WINDOWS)
 #  if defined(_MSC_VER) || (defined(__BORLANDC__) && !defined(__clang__))
 #   pragma message( \
@@ -753,15 +753,10 @@
 #   endif // !defined(_WINSOCK2API_)
 #  endif // defined(__WIN32__) && !defined(WIN32)
 # endif // defined(__BORLANDC__)
-# if defined(__CYGWIN__)
-#  if !defined(__USE_W32_SOCKETS)
-#   error You must add -D__USE_W32_SOCKETS to your compiler options.
-#  endif // !defined(__USE_W32_SOCKETS)
-# endif // defined(__CYGWIN__)
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 
 // Windows: minimise header inclusion.
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # if !defined(BOOST_ASIO_NO_WIN32_LEAN_AND_MEAN)
 #  if !defined(WIN32_LEAN_AND_MEAN)
 #   define WIN32_LEAN_AND_MEAN
@@ -770,7 +765,7 @@
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 
 // Windows: suppress definition of "min" and "max" macros.
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # if !defined(BOOST_ASIO_NO_NOMINMAX)
 #  if !defined(NOMINMAX)
 #   define NOMINMAX 1
@@ -780,7 +775,7 @@
 
 // Windows: IO Completion Ports.
 #if !defined(BOOST_ASIO_HAS_IOCP)
-# if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+# if defined(BOOST_ASIO_WINDOWS)
 #  if defined(_WIN32_WINNT) && (_WIN32_WINNT >= 0x0400)
 #   if !defined(UNDER_CE) && !defined(BOOST_ASIO_WINDOWS_APP)
 #    if !defined(BOOST_ASIO_DISABLE_IOCP)
@@ -882,8 +877,7 @@
 #if !defined(BOOST_ASIO_HAS_SERIAL_PORT)
 # if defined(BOOST_ASIO_HAS_IOCP) \
   || !defined(BOOST_ASIO_WINDOWS) \
-  && !defined(BOOST_ASIO_WINDOWS_RUNTIME) \
-  && !defined(__CYGWIN__)
+  && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 #  if !defined(__SYMBIAN32__)
 #   if !defined(BOOST_ASIO_DISABLE_SERIAL_PORT)
 #    define BOOST_ASIO_HAS_SERIAL_PORT 1
@@ -916,7 +910,7 @@
 // Windows: object handles.
 #if !defined(BOOST_ASIO_HAS_WINDOWS_OBJECT_HANDLE)
 # if !defined(BOOST_ASIO_DISABLE_WINDOWS_OBJECT_HANDLE)
-#  if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#  if defined(BOOST_ASIO_WINDOWS)
 #   if !defined(UNDER_CE) && !defined(BOOST_ASIO_WINDOWS_APP)
 #    define BOOST_ASIO_HAS_WINDOWS_OBJECT_HANDLE 1
 #   endif // !defined(UNDER_CE) && !defined(BOOST_ASIO_WINDOWS_APP)
@@ -937,8 +931,7 @@
 #if !defined(BOOST_ASIO_HAS_POSIX_STREAM_DESCRIPTOR)
 # if !defined(BOOST_ASIO_DISABLE_POSIX_STREAM_DESCRIPTOR)
 #  if !defined(BOOST_ASIO_WINDOWS) \
-  && !defined(BOOST_ASIO_WINDOWS_RUNTIME) \
-  && !defined(__CYGWIN__)
+  && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 #   define BOOST_ASIO_HAS_POSIX_STREAM_DESCRIPTOR 1
 #  endif // !defined(BOOST_ASIO_WINDOWS)
          //   && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
@@ -970,8 +963,7 @@
 #if !defined(BOOST_ASIO_HAS_PIPE)
 # if defined(BOOST_ASIO_HAS_IOCP) \
   || !defined(BOOST_ASIO_WINDOWS) \
-  && !defined(BOOST_ASIO_WINDOWS_RUNTIME) \
-  && !defined(__CYGWIN__)
+  && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 #  if !defined(__SYMBIAN32__)
 #   if !defined(BOOST_ASIO_DISABLE_PIPE)
 #    define BOOST_ASIO_HAS_PIPE 1
@@ -987,8 +979,7 @@
 #if !defined(BOOST_ASIO_HAS_SIGACTION)
 # if !defined(BOOST_ASIO_DISABLE_SIGACTION)
 #  if !defined(BOOST_ASIO_WINDOWS) \
-  && !defined(BOOST_ASIO_WINDOWS_RUNTIME) \
-  && !defined(__CYGWIN__)
+  && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 #   define BOOST_ASIO_HAS_SIGACTION 1
 #  endif // !defined(BOOST_ASIO_WINDOWS)
          //   && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
@@ -1008,7 +999,7 @@
 // Can use getaddrinfo() and getnameinfo().
 #if !defined(BOOST_ASIO_HAS_GETADDRINFO)
 # if !defined(BOOST_ASIO_DISABLE_GETADDRINFO)
-#  if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#  if defined(BOOST_ASIO_WINDOWS)
 #   if defined(_WIN32_WINNT) && (_WIN32_WINNT >= 0x0501)
 #    define BOOST_ASIO_HAS_GETADDRINFO 1
 #   elif defined(UNDER_CE)
diff --git a/include/boost/asio/detail/fd_set_adapter.hpp b/include/boost/asio/detail/fd_set_adapter.hpp
index 9633b73fa..a9bcee17d 100644
--- a/include/boost/asio/detail/fd_set_adapter.hpp
+++ b/include/boost/asio/detail/fd_set_adapter.hpp
@@ -26,7 +26,7 @@ namespace boost {
 namespace asio {
 namespace detail {
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 typedef win_fd_set_adapter fd_set_adapter;
 #else
 typedef posix_fd_set_adapter fd_set_adapter;
diff --git a/include/boost/asio/detail/hash_map.hpp b/include/boost/asio/detail/hash_map.hpp
index 41a2cbe25..439565815 100644
--- a/include/boost/asio/detail/hash_map.hpp
+++ b/include/boost/asio/detail/hash_map.hpp
@@ -21,7 +21,7 @@
 #include <boost/asio/detail/assert.hpp>
 #include <boost/asio/detail/noncopyable.hpp>
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # include <boost/asio/detail/socket_types.hpp>
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 
@@ -42,7 +42,7 @@ inline std::size_t calculate_hash_value(void* p)
     + (reinterpret_cast<std::size_t>(p) >> 3);
 }
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 inline std::size_t calculate_hash_value(SOCKET s)
 {
   return static_cast<std::size_t>(s);
diff --git a/include/boost/asio/detail/impl/null_event.ipp b/include/boost/asio/detail/impl/null_event.ipp
index 9fa70363f..84fab35c5 100644
--- a/include/boost/asio/detail/impl/null_event.ipp
+++ b/include/boost/asio/detail/impl/null_event.ipp
@@ -19,7 +19,7 @@
 
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
 # include <thread>
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
 # include <boost/asio/detail/socket_types.hpp>
 #else
 # include <unistd.h>
@@ -41,7 +41,7 @@ void null_event::do_wait()
 {
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
   std::this_thread::sleep_until((std::chrono::steady_clock::time_point::max)());
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
   ::Sleep(INFINITE);
 #else
   ::pause();
@@ -52,7 +52,7 @@ void null_event::do_wait_for_usec(long usec)
 {
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
   std::this_thread::sleep_for(std::chrono::microseconds(usec));
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
   ::Sleep(usec / 1000);
 #elif defined(__hpux) && defined(__SELECT)
   timespec ts;
diff --git a/include/boost/asio/detail/impl/socket_ops.ipp b/include/boost/asio/detail/impl/socket_ops.ipp
index 0129511c9..770a9600c 100644
--- a/include/boost/asio/detail/impl/socket_ops.ipp
+++ b/include/boost/asio/detail/impl/socket_ops.ipp
@@ -33,7 +33,7 @@
 # include <string>
 #endif // defined(BOOST_ASIO_WINDOWS_RUNTIME)
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__) \
+#if defined(BOOST_ASIO_WINDOWS) \
   || defined(__MACH__) && defined(__APPLE__)
 # if defined(BOOST_ASIO_HAS_PTHREADS)
 #  include <pthread.h>
@@ -54,7 +54,7 @@ namespace socket_ops {
 
 #if !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 struct msghdr { int msg_namelen; };
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 
@@ -69,7 +69,7 @@ extern "C" unsigned int if_nametoindex(const char*);
 
 inline void clear_last_error()
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   WSASetLastError(0);
 #else
   errno = 0;
@@ -87,7 +87,7 @@ inline void get_last_error(
   }
   else
   {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
     ec = boost::system::error_code(WSAGetLastError(),
         boost::asio::error::get_system_category());
 #else
@@ -317,7 +317,7 @@ int close(socket_type s, state_type& state,
           SO_LINGER, &opt, sizeof(opt), ignored_ec);
     }
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
     result = ::closesocket(s);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
     result = ::close(s);
@@ -334,7 +334,7 @@ int close(socket_type s, state_type& state,
       // current OS where this behaviour is seen, Windows, says that the socket
       // remains open. Therefore we'll put the descriptor back into blocking
       // mode and have another attempt at closing it.
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
       ioctl_arg_type arg = 0;
       ::ioctlsocket(s, FIONBIO, &arg);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
@@ -366,7 +366,7 @@ int close(socket_type s, state_type& state,
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
       state &= ~non_blocking;
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
       result = ::closesocket(s);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
       result = ::close(s);
@@ -387,7 +387,7 @@ bool set_user_non_blocking(socket_type s,
     return false;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   ioctl_arg_type arg = (value ? 1 : 0);
   int result = ::ioctlsocket(s, FIONBIO, &arg);
   get_last_error(ec, result < 0);
@@ -463,7 +463,7 @@ bool set_internal_non_blocking(socket_type s,
     return false;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   ioctl_arg_type arg = (value ? 1 : 0);
   int result = ::ioctlsocket(s, FIONBIO, &arg);
   get_last_error(ec, result < 0);
@@ -629,7 +629,6 @@ bool non_blocking_connect(socket_type s, boost::system::error_code& ec)
   // Check if the connect operation has finished. This is required since we may
   // get spurious readiness notifications from the reactor.
 #if defined(BOOST_ASIO_WINDOWS) \
-  || defined(__CYGWIN__) \
   || defined(__SYMBIAN32__)
   fd_set write_fds;
   FD_ZERO(&write_fds);
@@ -679,7 +678,7 @@ bool non_blocking_connect(socket_type s, boost::system::error_code& ec)
 int socketpair(int af, int type, int protocol,
     socket_type sv[2], boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   (void)(af);
   (void)(type);
   (void)(protocol);
@@ -703,7 +702,7 @@ bool sockatmark(socket_type s, boost::system::error_code& ec)
 
 #if defined(SIOCATMARK)
   ioctl_arg_type value = 0;
-# if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+# if defined(BOOST_ASIO_WINDOWS)
   int result = ::ioctlsocket(s, SIOCATMARK, &value);
 # else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   int result = ::ioctl(s, SIOCATMARK, &value);
@@ -730,7 +729,7 @@ size_t available(socket_type s, boost::system::error_code& ec)
   }
 
   ioctl_arg_type value = 0;
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   int result = ::ioctlsocket(s, FIONREAD, &value);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   int result = ::ioctl(s, FIONREAD, &value);
@@ -768,7 +767,7 @@ inline void init_buf_iov_base(T& base, void* addr)
   base = static_cast<T>(addr);
 }
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 typedef WSABUF buf;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 typedef iovec buf;
@@ -776,7 +775,7 @@ typedef iovec buf;
 
 void init_buf(buf& b, void* data, size_t size)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   b.buf = static_cast<char*>(data);
   b.len = static_cast<u_long>(size);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
@@ -787,7 +786,7 @@ void init_buf(buf& b, void* data, size_t size)
 
 void init_buf(buf& b, const void* data, size_t size)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   b.buf = static_cast<char*>(const_cast<void*>(data));
   b.len = static_cast<u_long>(size);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
@@ -821,7 +820,7 @@ inline void init_msghdr_msg_name(T& name, const void* addr)
 signed_size_type recv(socket_type s, buf* bufs, size_t count,
     int flags, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Receive some data.
   DWORD recv_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
@@ -852,7 +851,7 @@ signed_size_type recv(socket_type s, buf* bufs, size_t count,
 signed_size_type recv1(socket_type s, void* data, size_t size,
     int flags, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Receive some data.
   WSABUF buf;
   buf.buf = const_cast<char*>(static_cast<const char*>(data));
@@ -1084,7 +1083,7 @@ bool non_blocking_recv1(socket_type s,
 signed_size_type recvfrom(socket_type s, buf* bufs, size_t count,
     int flags, void* addr, std::size_t* addrlen, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Receive some data.
   DWORD recv_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
@@ -1132,7 +1131,7 @@ inline signed_size_type call_recvfrom(SockLenType msghdr::*, socket_type s,
 signed_size_type recvfrom1(socket_type s, void* data, size_t size,
     int flags, void* addr, std::size_t* addrlen, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Receive some data.
   WSABUF buf;
   buf.buf = static_cast<char*>(data);
@@ -1321,7 +1320,7 @@ bool non_blocking_recvfrom1(socket_type s, void* data,
 signed_size_type recvmsg(socket_type s, buf* bufs, size_t count,
     int in_flags, int& out_flags, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   out_flags = 0;
   return socket_ops::recv(s, bufs, count, in_flags, ec);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
@@ -1434,7 +1433,7 @@ bool non_blocking_recvmsg(socket_type s,
 signed_size_type send(socket_type s, const buf* bufs, size_t count,
     int flags, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Send the data.
   DWORD send_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
@@ -1466,7 +1465,7 @@ signed_size_type send(socket_type s, const buf* bufs, size_t count,
 signed_size_type send1(socket_type s, const void* data, size_t size,
     int flags, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Send the data.
   WSABUF buf;
   buf.buf = const_cast<char*>(static_cast<const char*>(data));
@@ -1661,7 +1660,7 @@ signed_size_type sendto(socket_type s, const buf* bufs,
     size_t count, int flags, const void* addr,
     std::size_t addrlen, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Send the data.
   DWORD send_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
@@ -1706,7 +1705,7 @@ signed_size_type sendto1(socket_type s, const void* data,
     size_t size, int flags, const void* addr,
     std::size_t addrlen, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   // Send the data.
   WSABUF buf;
   buf.buf = const_cast<char*>(static_cast<const char*>(data));
@@ -1874,7 +1873,7 @@ bool non_blocking_sendto1(socket_type s,
 socket_type socket(int af, int type, int protocol,
     boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   socket_type s = ::WSASocketW(af, type, protocol, 0, 0, WSA_FLAG_OVERLAPPED);
   get_last_error(ec, s == invalid_socket);
   if (s == invalid_socket)
@@ -2071,7 +2070,7 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
   }
   ec = boost::asio::error::fault;
   return socket_error_retval;
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
   int result = call_getsockopt(&msghdr::msg_namelen,
         s, level, optname, optval, optlen);
   get_last_error(ec, result != 0);
@@ -2127,8 +2126,7 @@ int getpeername(socket_type s, void* addr, std::size_t* addrlen,
     return socket_error_retval;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) && !defined(BOOST_ASIO_WINDOWS_APP) \
-  || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS) && !defined(BOOST_ASIO_WINDOWS_APP)
   if (cached)
   {
     // Check if socket is still connected.
@@ -2194,7 +2192,7 @@ int ioctl(socket_type s, state_type& state, int cmd,
     return socket_error_retval;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   int result = ::ioctlsocket(s, cmd, arg);
 #elif defined(__MACH__) && defined(__APPLE__) \
   || defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
@@ -2235,7 +2233,7 @@ int select(int nfds, fd_set* readfds, fd_set* writefds,
 #if defined(__EMSCRIPTEN__)
   exceptfds = 0;
 #endif // defined(__EMSCRIPTEN__)
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   if (!readfds && !writefds && !exceptfds && timeout)
   {
     DWORD milliseconds = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;
@@ -2279,8 +2277,7 @@ int poll_read(socket_type s, state_type state,
     return socket_error_retval;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) \
-  || defined(__CYGWIN__) \
+#if defined(BOOST_ASIO_WINDOWS)
   || defined(__SYMBIAN32__)
   fd_set fds;
   FD_ZERO(&fds);
@@ -2331,8 +2328,7 @@ int poll_write(socket_type s, state_type state,
     return socket_error_retval;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) \
-  || defined(__CYGWIN__) \
+#if defined(BOOST_ASIO_WINDOWS)
   || defined(__SYMBIAN32__)
   fd_set fds;
   FD_ZERO(&fds);
@@ -2383,8 +2379,7 @@ int poll_error(socket_type s, state_type state,
     return socket_error_retval;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) \
-  || defined(__CYGWIN__) \
+#if defined(BOOST_ASIO_WINDOWS)
   || defined(__SYMBIAN32__)
   fd_set fds;
   FD_ZERO(&fds);
@@ -2434,8 +2429,7 @@ int poll_connect(socket_type s, int msec, boost::system::error_code& ec)
     return socket_error_retval;
   }
 
-#if defined(BOOST_ASIO_WINDOWS) \
-  || defined(__CYGWIN__) \
+#if defined(BOOST_ASIO_WINDOWS)
   || defined(__SYMBIAN32__)
   fd_set write_fds;
   FD_ZERO(&write_fds);
@@ -2512,7 +2506,7 @@ const char* inet_ntop(int af, const void* src, char* dest, size_t length,
     ec = boost::asio::error::address_family_not_supported;
     return 0;
   }
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
   using namespace std; // For memcpy.
 
   if (af != BOOST_ASIO_OS_DEF(AF_INET) && af != BOOST_ASIO_OS_DEF(AF_INET6))
@@ -2746,7 +2740,7 @@ int inet_pton(int af, const char* src, void* dest,
     ec = boost::asio::error::address_family_not_supported;
     return -1;
   }
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
   using namespace std; // For memcpy and strcmp.
 
   if (af != BOOST_ASIO_OS_DEF(AF_INET) && af != BOOST_ASIO_OS_DEF(AF_INET6))
@@ -3773,7 +3767,7 @@ inline boost::system::error_code translate_addrinfo_error(int error)
   case EAI_SOCKTYPE:
     return boost::asio::error::socket_type_not_supported;
   default: // Possibly the non-portable EAI_SYSTEM.
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
     return boost::system::error_code(
         WSAGetLastError(), boost::asio::error::get_system_category());
 #else
@@ -3790,7 +3784,7 @@ boost::system::error_code getaddrinfo(const char* host,
   host = (host && *host) ? host : 0;
   service = (service && *service) ? service : 0;
   clear_last_error();
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # if defined(BOOST_ASIO_HAS_GETADDRINFO)
   // Building for Windows XP, Windows Server 2003, or later.
   int error = ::getaddrinfo(host, service, &hints, result);
@@ -3864,7 +3858,7 @@ boost::system::error_code background_getaddrinfo(
 
 void freeaddrinfo(addrinfo_type* ai)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # if defined(BOOST_ASIO_HAS_GETADDRINFO)
   // Building for Windows XP, Windows Server 2003, or later.
   ::freeaddrinfo(ai);
@@ -3892,7 +3886,7 @@ boost::system::error_code getnameinfo(const void* addr,
     std::size_t addrlen, char* host, std::size_t hostlen,
     char* serv, std::size_t servlen, int flags, boost::system::error_code& ec)
 {
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # if defined(BOOST_ASIO_HAS_GETADDRINFO)
   // Building for Windows XP, Windows Server 2003, or later.
   clear_last_error();
diff --git a/include/boost/asio/detail/posix_fd_set_adapter.hpp b/include/boost/asio/detail/posix_fd_set_adapter.hpp
index ee316c239..e69271af3 100644
--- a/include/boost/asio/detail/posix_fd_set_adapter.hpp
+++ b/include/boost/asio/detail/posix_fd_set_adapter.hpp
@@ -18,7 +18,6 @@
 #include <boost/asio/detail/config.hpp>
 
 #if !defined(BOOST_ASIO_WINDOWS) \
-  && !defined(__CYGWIN__) \
   && !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 
 #include <cstring>
diff --git a/include/boost/asio/detail/select_reactor.hpp b/include/boost/asio/detail/select_reactor.hpp
index befb63d70..87004b16c 100644
--- a/include/boost/asio/detail/select_reactor.hpp
+++ b/include/boost/asio/detail/select_reactor.hpp
@@ -55,7 +55,7 @@ class select_reactor
 #endif // !defined(BOOST_ASIO_HAS_IOCP)
 {
 public:
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   enum op_types { read_op = 0, write_op = 1, except_op = 2,
     max_select_ops = 3, connect_op = 3, max_ops = 4 };
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
diff --git a/include/boost/asio/detail/socket_ops.hpp b/include/boost/asio/detail/socket_ops.hpp
index af3595c7a..a3327572b 100644
--- a/include/boost/asio/detail/socket_ops.hpp
+++ b/include/boost/asio/detail/socket_ops.hpp
@@ -129,7 +129,7 @@ BOOST_ASIO_DECL size_t available(socket_type s, boost::system::error_code& ec);
 BOOST_ASIO_DECL int listen(socket_type s,
     int backlog, boost::system::error_code& ec);
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 typedef WSABUF buf;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 typedef iovec buf;
diff --git a/include/boost/asio/detail/socket_types.hpp b/include/boost/asio/detail/socket_types.hpp
index 972d4b20b..5a7203b3a 100644
--- a/include/boost/asio/detail/socket_types.hpp
+++ b/include/boost/asio/detail/socket_types.hpp
@@ -19,7 +19,7 @@
 
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
 // Empty.
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
 # if defined(_WINSOCKAPI_) && !defined(_WINSOCK2API_)
 #  error WinSock.h has already been included
 # endif // defined(_WINSOCKAPI_) && !defined(_WINSOCK2API_)
@@ -183,7 +183,7 @@ typedef int signed_size_type;
 # define BOOST_ASIO_OS_DEF_SA_RESTART 0x1
 # define BOOST_ASIO_OS_DEF_SA_NOCLDSTOP 0x2
 # define BOOST_ASIO_OS_DEF_SA_NOCLDWAIT 0x4
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
 typedef SOCKET socket_type;
 const SOCKET invalid_socket = INVALID_SOCKET;
 const int socket_error_retval = SOCKET_ERROR;
diff --git a/include/boost/asio/detail/win_fd_set_adapter.hpp b/include/boost/asio/detail/win_fd_set_adapter.hpp
index 64e782d8e..f4ccab0dd 100644
--- a/include/boost/asio/detail/win_fd_set_adapter.hpp
+++ b/include/boost/asio/detail/win_fd_set_adapter.hpp
@@ -17,7 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 
 #include <boost/asio/detail/noncopyable.hpp>
 #include <boost/asio/detail/reactor_op_queue.hpp>
diff --git a/include/boost/asio/error.hpp b/include/boost/asio/error.hpp
index 10030e166..943fb5265 100644
--- a/include/boost/asio/error.hpp
+++ b/include/boost/asio/error.hpp
@@ -20,7 +20,6 @@
 #include <boost/system/error_code.hpp>
 #include <boost/system/system_error.hpp>
 #if defined(BOOST_ASIO_WINDOWS) \
-  || defined(__CYGWIN__) \
   || defined(BOOST_ASIO_WINDOWS_RUNTIME)
 # include <winerror.h>
 #else
@@ -45,7 +44,7 @@
 # define BOOST_ASIO_NETDB_ERROR(e) __HRESULT_FROM_WIN32(WSA ## e)
 # define BOOST_ASIO_GETADDRINFO_ERROR(e) __HRESULT_FROM_WIN32(WSA ## e)
 # define BOOST_ASIO_WIN_OR_POSIX(e_win, e_posix) e_win
-#elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#elif defined(BOOST_ASIO_WINDOWS)
 # define BOOST_ASIO_NATIVE_ERROR(e) e
 # define BOOST_ASIO_SOCKET_ERROR(e) WSA ## e
 # define BOOST_ASIO_NETDB_ERROR(e) WSA ## e
@@ -259,7 +258,7 @@ inline const boost::system::error_category& get_system_category()
   return boost::system::system_category();
 }
 
-#if !defined(BOOST_ASIO_WINDOWS) && !defined(__CYGWIN__)
+#if !defined(BOOST_ASIO_WINDOWS)
 
 extern BOOST_ASIO_DECL
 const boost::system::error_category& get_netdb_category();
@@ -267,7 +266,7 @@ const boost::system::error_category& get_netdb_category();
 extern BOOST_ASIO_DECL
 const boost::system::error_category& get_addrinfo_category();
 
-#else // !defined(BOOST_ASIO_WINDOWS) && !defined(__CYGWIN__)
+#else // !defined(BOOST_ASIO_WINDOWS)
 
 inline const boost::system::error_category& get_netdb_category()
 {
@@ -279,7 +278,7 @@ inline const boost::system::error_category& get_addrinfo_category()
   return get_system_category();
 }
 
-#endif // !defined(BOOST_ASIO_WINDOWS) && !defined(__CYGWIN__)
+#endif // !defined(BOOST_ASIO_WINDOWS)
 
 extern BOOST_ASIO_DECL
 const boost::system::error_category& get_misc_category();
diff --git a/include/boost/asio/impl/error.ipp b/include/boost/asio/impl/error.ipp
index bb70b3623..4b8f0e72a 100644
--- a/include/boost/asio/impl/error.ipp
+++ b/include/boost/asio/impl/error.ipp
@@ -25,7 +25,7 @@ namespace boost {
 namespace asio {
 namespace error {
 
-#if !defined(BOOST_ASIO_WINDOWS) && !defined(__CYGWIN__)
+#if !defined(BOOST_ASIO_WINDOWS)
 
 namespace detail {
 
diff --git a/include/boost/asio/io_context.hpp b/include/boost/asio/io_context.hpp
index f4769bb4d..9d4130df5 100644
--- a/include/boost/asio/io_context.hpp
+++ b/include/boost/asio/io_context.hpp
@@ -28,7 +28,7 @@
 #include <boost/asio/execution.hpp>
 #include <boost/asio/execution_context.hpp>
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
 # include <boost/asio/detail/winsock_init.hpp>
 #elif defined(__sun) || defined(__QNX__) || defined(__hpux) || defined(_AIX) \
   || defined(__osf__)
@@ -517,7 +517,7 @@ class io_context
   template <typename Service>
   friend Service& use_service(io_context& ioc);
 
-#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(BOOST_ASIO_WINDOWS)
   detail::winsock_init<> init_;
 #elif defined(__sun) || defined(__QNX__) || defined(__hpux) || defined(_AIX) \
   || defined(__osf__)