back-ported dbghlp fix (#946)

back-ported dbghlp fix

src/assert.cpp

@@ -146,12 +146,19 @@ TORRENT_EXPORT void print_backtrace(char* out, int len, int max_depth)
 
 #include "windows.h"
 #include "libtorrent/utf8.hpp"
+#include "libtorrent/thread.hpp"
 
 #include "winbase.h"
 #include "dbghelp.h"
 
+static libtorrent::mutex dbghlp_mutex;
+
 TORRENT_EXPORT void print_backtrace(char* out, int len, int max_depth)
 {
+	// all calls to DbgHlp.dll are thread-unsafe. i.e. they all need to be
+	// synchronized and not called concurrently. This mutex serializes access
+	libtorrent::mutex::scoped_lock l(dbghlp_mutex);
+
 	typedef USHORT (WINAPI *RtlCaptureStackBackTrace_t)(
 		__in ULONG FramesToSkip,
 		__in ULONG FramesToCapture,

test/main.cpp

@@ -51,6 +51,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <windows.h> // fot SetErrorMode
 #include <io.h> // for _dup and _dup2
 #include <process.h> // for _getpid
+#include <crtdbg.h>
 
 #define dup _dup
 #define dup2 _dup2
@@ -224,6 +225,12 @@ EXPORT int main(int argc, char const* argv[])
 		| SEM_NOGPFAULTERRORBOX | SEM_NOOPENFILEERRORBOX);
 
 	SetUnhandledExceptionFilter(&seh_exception_handler);
+
+#ifdef _DEBUG
+	_CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE);
+	_CrtSetReportFile(_CRT_ERROR, _CRTDBG_FILE_STDERR);
+#endif
+
 #endif
 
 #ifdef O_NONBLOCK