Implement BasicThread::IsMainThread

Add support to discriminate between the main thread and other threads on the system.  Some systems have special handling for the main thread--IE, certain APIs can only be called safely from it--thus it's important that we have a way to inform such systems as to whether a particular thread is the main thread.

autowiring/BasicThread.h

@@ -308,6 +308,11 @@ class BasicThread:
   /// \include snippets/BasicThread_GetRunningTime.txt
   /// </remarks>
   void GetThreadTimes(std::chrono::milliseconds& kernelTime, std::chrono::milliseconds& userTime);
+
+  /// <returns>
+  /// True if the calling thread is the main thread
+  /// </returns>
+  static bool IsMainThread(void);
 };
 
 /// <summary>

src/autowiring/BasicThreadUnix.cpp

@@ -0,0 +1,8 @@
+// Copyright (C) 2012-2015 Leap Motion, Inc. All rights reserved.
+#include "stdafx.h"
+#include "BasicThread.h"
+#include <unistd.h>
+
+bool BasicThread::IsMainThread(void) {
+  return getpid() == gettid();
+}

src/autowiring/BasicThreadWin.cpp

@@ -0,0 +1,10 @@
+// Copyright (C) 2012-2015 Leap Motion, Inc. All rights reserved.
+#include "stdafx.h"
+#include "BasicThread.h"
+#include <Windows.h>
+
+static int s_mainTID = GetCurrentThreadId();
+
+bool BasicThread::IsMainThread(void) {
+  return GetCurrentThreadId() == s_mainTID;
+}

src/autowiring/CMakeLists.txt

@@ -189,6 +189,7 @@ add_conditional_sources(
 
 add_windows_sources(Autowiring_SRCS
   auto_future_win.h
+  BasicThreadWin.cpp
   CoreThreadWin.cpp
   SystemThreadPoolWin.cpp
   SystemThreadPoolWin.h
@@ -203,6 +204,7 @@ add_mac_sources(Autowiring_SRCS
 
 add_unix_sources(Autowiring_SRCS
   InterlockedExchangeUnix.cpp
+  BasicThreadUnix.cpp
   thread_specific_ptr_unix.h
 )
 

src/autowiring/test/BasicThreadTest.cpp

@@ -1,6 +1,7 @@
 // Copyright (C) 2012-2015 Leap Motion, Inc. All rights reserved.
 #include "stdafx.h"
 #include <autowiring/BasicThread.h>
+#include FUTURE_HEADER
 
 class BasicThreadTest:
   public testing::Test
@@ -64,3 +65,14 @@ TEST_F(BasicThreadTest, ValidateThreadTimes) {
   ASSERT_LE(benchmark, spinsThenQuits->m_userTime * 10) <<
     "Reported execution time could not possibly be correct, spin operation took less time to execute than should have been possible with the CPU";
 }
+
+TEST_F(BasicThreadTest, IsMainThread) {
+  ASSERT_TRUE(BasicThread::IsMainThread()) << "Main thread not correctly identified as the main thread";
+  std::future<bool> secondaryIsMain = std::async(
+    std::launch::async,
+    [] {
+      return BasicThread::IsMainThread();
+    }
+  );
+  ASSERT_FALSE(secondaryIsMain.get()) << "Secondary thread incorrectly identified as the main thread";
+}