Allow using WindowsThread with Mingw (#8108)

Summary:
Allow using WindowsThread with Mingw

Most Mingw builds require Posix threads in order to use std::thread.
As per https://github.com/facebook/rocksdb/issues/7764, this is not always the case.

That being considered, we're going to improve the Mingw thread model
checks.

Closes: https://github.com/facebook/rocksdb/issues/7764
Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8108

Reviewed By: jay-zhuang

Differential Revision: D27365778

Pulled By: mrambacher

fbshipit-source-id: 2c15b1f04ae90e1e3a25a33e86ceb779224a9529

CMakeLists.txt

@@ -934,13 +934,8 @@ if(WIN32)
     port/win/env_win.cc
     port/win/env_default.cc
     port/win/port_win.cc
-    port/win/win_logger.cc)
-  if(NOT MINGW)
-    # Mingw only supports std::thread when using
-    # posix threads.
-    list(APPEND SOURCES
-      port/win/win_thread.cc)
-  endif()
+    port/win/win_logger.cc
+    port/win/win_thread.cc)
 if(WITH_XPRESS)
   list(APPEND SOURCES
     port/win/xpress_win.cc)

port/win/env_win.cc

@@ -30,7 +30,6 @@
 #include "port/win/env_win.h"
 #include "port/win/io_win.h"
 #include "port/win/win_logger.h"
-#include "port/win/win_thread.h"
 #include "rocksdb/env.h"
 #include "rocksdb/slice.h"
 #include "strsafe.h"
@@ -1291,7 +1290,7 @@ void WinEnvThreads::StartThread(void (*function)(void* arg), void* arg) {
   state->user_function = function;
   state->arg = arg;
   try {
-    ROCKSDB_NAMESPACE::port::WindowsThread th(&StartThreadWrapper, state.get());
+    Thread th(&StartThreadWrapper, state.get());
     state.release();
 
     std::lock_guard<std::mutex> lg(mu_);

port/win/env_win.h

@@ -23,7 +23,7 @@
 #include <vector>
 
 #include "env/composite_env_wrapper.h"
-#include "port/win/win_thread.h"
+#include "port/port.h"
 #include "rocksdb/env.h"
 #include "rocksdb/file_system.h"
 #include "rocksdb/system_clock.h"
@@ -71,7 +71,7 @@ class WinEnvThreads {
   Env* hosted_env_;
   mutable std::mutex mu_;
   std::vector<ThreadPoolImpl> thread_pools_;
-  std::vector<WindowsThread> threads_to_join_;
+  std::vector<Thread> threads_to_join_;
 };
 
 class WinClock : public SystemClock {

port/win/win_thread.cc

@@ -8,6 +8,11 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #if defined(OS_WIN)
+// Most Mingw builds support std::thread only when using posix threads.
+// In that case, some of these functions will be unavailable.
+// Note that we're using either WindowsThread or std::thread, depending on
+// which one is available.
+#ifndef _POSIX_THREADS
 
 #include "port/win/win_thread.h"
 
@@ -180,4 +185,5 @@ unsigned int __stdcall  WindowsThread::Data::ThreadProc(void* arg) {
 } // namespace port
 }  // namespace ROCKSDB_NAMESPACE
 
-#endif
+#endif  // OS_WIN
+#endif  // !_POSIX_THREADS

port/win/win_thread.h

@@ -9,6 +9,8 @@
 
 #pragma once
 
+#ifndef _POSIX_THREADS
+
 #include <memory>
 #include <functional>
 #include <type_traits>
@@ -120,3 +122,4 @@ inline void swap(ROCKSDB_NAMESPACE::port::WindowsThread& th1,
 }
 } // namespace std
 
+#endif  // !_POSIX_THREADS