Increase thread stack for OS X (official-stockfish#2035)

On OS X threads other than the main thread are created with a reduced stack
size of 512KB by default, this is dangerously low for deep searches, so
adjust it to TH_STACK_SIZE. The implementation calls pthread_create() with
proper stack size parameter.

Verified for no regression at STC enabling the patch on all platforms where
pthread is supported.

LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 50873 W: 9768 L: 9700 D: 31405

No functional change.

src/syzygy/tbprobe.cpp

@@ -32,7 +32,7 @@
 #include "../movegen.h"
 #include "../position.h"
 #include "../search.h"
-#include "../thread_win32.h"
+#include "../thread_win32_osx.h"
 #include "../types.h"
 #include "../uci.h"
 

src/thread.h

@@ -32,7 +32,7 @@
 #include "pawns.h"
 #include "position.h"
 #include "search.h"
-#include "thread_win32.h"
+#include "thread_win32_osx.h"
 
 
 /// Thread class keeps together all the thread-related stuff. We use
@@ -46,7 +46,7 @@ class Thread {
   ConditionVariable cv;
   size_t idx;
   bool exit = false, searching = true; // Set before starting std::thread
-  std::thread stdThread;
+  NativeThread stdThread;
 
 public:
   explicit Thread(size_t);

src/thread_win32.h → src/thread_win32_osx.h

@@ -18,8 +18,8 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#ifndef THREAD_WIN32_H_INCLUDED
-#define THREAD_WIN32_H_INCLUDED
+#ifndef THREAD_WIN32_OSX_H_INCLUDED
+#define THREAD_WIN32_OSX_H_INCLUDED
 
 /// STL thread library used by mingw and gcc when cross compiling for Windows
 /// relies on libwinpthread. Currently libwinpthread implements mutexes directly
@@ -33,6 +33,7 @@
 
 #include <condition_variable>
 #include <mutex>
+#include <thread>
 
 #if defined(_WIN32) && !defined(_MSC_VER)
 
@@ -67,4 +68,45 @@ typedef std::condition_variable ConditionVariable;
 
 #endif
 
-#endif // #ifndef THREAD_WIN32_H_INCLUDED
+/// On OSX threads other than the main thread are created with a reduced stack
+/// size of 512KB by default, this is dangerously low for deep searches, so
+/// adjust it to TH_STACK_SIZE. The implementation calls pthread_create() with
+/// proper stack size parameter.
+
+#if defined(__APPLE__)
+
+#include <pthread.h>
+
+static const size_t TH_STACK_SIZE = 2 * 1024 * 1024;
+
+template <class T, class P = std::pair<T*, void(T::*)()>>
+void* start_routine(void* ptr)
+{
+   P* p = reinterpret_cast<P*>(ptr);
+   (p->first->*(p->second))(); // Call member function pointer
+   delete p;
+   return NULL;
+}
+
+class NativeThread {
+
+   pthread_t thread;
+
+public:
+  template<class T, class P = std::pair<T*, void(T::*)()>>
+  explicit NativeThread(void(T::*fun)(), T* obj) {
+    pthread_attr_t attr_storage, *attr = &attr_storage;
+    pthread_attr_init(attr);
+    pthread_attr_setstacksize(attr, TH_STACK_SIZE);
+    pthread_create(&thread, attr, start_routine<T>, new P(obj, fun));
+  }
+  void join() { pthread_join(thread, NULL); }
+};
+
+#else // Default case: use STL classes
+
+typedef std::thread NativeThread;
+
+#endif
+
+#endif // #ifndef THREAD_WIN32_OSX_H_INCLUDED