Posix threads (#6865)

Summary:
Rocksdb is using the c++11 std::threads feature. The issue is that
MINGW only supports it when using Posix threads.

This change will allow rocksdb::port::WindowsThread to be replaced
with std::thread, which in turn will allow Rocksdb to be cross
compiled using MINGW.

At the same time, we'll have to use GetCurrentProcessId instead of _getpid.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6865

Reviewed By: cheng-chang

Differential Revision: D21864285

Pulled By: ajkr

fbshipit-source-id: 0982eed313e7d34d351b1364c1ccc722da473205

CMakeLists.txt

@@ -804,9 +804,13 @@ if(WIN32)
     port/win/env_win.cc
     port/win/env_default.cc
     port/win/port_win.cc
-    port/win/win_logger.cc
-    port/win/win_thread.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()
 if(WITH_XPRESS)
   list(APPEND SOURCES
     port/win/xpress_win.cc)

port/win/env_win.cc

@@ -14,7 +14,6 @@
 #include <thread>
 
 #include <errno.h>
-#include <process.h> // _getpid
 #include <io.h> // _access
 #include <direct.h> // _rmdir, _mkdir, _getcwd
 #include <sys/types.h>
@@ -906,7 +905,7 @@ Status WinEnvIO::GetTestDirectory(std::string* result) {
   CreateDir(output);
 
   output.append("\\testrocksdb-");
-  output.append(std::to_string(_getpid()));
+  output.append(std::to_string(GetCurrentProcessId()));
 
   CreateDir(output);
 

port/win/port_win.h

@@ -18,12 +18,14 @@
 
 #include <windows.h>
 #include <string>
+#include <thread>
 #include <string.h>
 #include <mutex>
 #include <limits>
 #include <condition_variable>
 #include <malloc.h>
 #include <intrin.h>
+#include <process.h>
 
 #include <stdint.h>
 
@@ -217,9 +219,14 @@ class CondVar {
   Mutex* mu_;
 };
 
+
+#ifdef _POSIX_THREADS
+using Thread = std::thread;
+#else
 // Wrapper around the platform efficient
 // or otherwise preferrable implementation
 using Thread = WindowsThread;
+#endif
 
 // OnceInit type helps emulate
 // Posix semantics with initialization