fixed race condition in iconv string converter

ChangeLog

@@ -72,6 +72,7 @@
 	  incoming connection
 	* added more detailed instrumentation of the disk I/O thread
 
+	* fixed race condition in iconv string converter
 	* fixed error handling in torrent_info constructor
 	* fixed bug in torrent_info::remap_files
 	* fix python binding for wait_for_alert

src/escape_string.cpp

@@ -55,6 +55,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #endif
 
 #include "libtorrent/utf8.hpp"
+#include "libtorrent/thread.hpp"
 
 #if TORRENT_USE_ICONV
 #include <iconv.h>
@@ -646,7 +647,7 @@ namespace libtorrent
 		char const* in = s.c_str();
 		char* out = &ret[0];
 #ifdef TORRENT_LINUX
-// linux seems to have a weird iconv signature
+// linux (and posix) seems to have a weird iconv signature
 #define ICONV_IN_CAST (char**)
 #else
 #define ICONV_IN_CAST
@@ -666,6 +667,10 @@ namespace libtorrent
 
 	std::string convert_to_native(std::string const& s)
 	{
+		static mutex iconv_mutex;
+		// only one thread can use this handle at a time
+		mutex::scoped_lock l(iconv_mutex);
+
 		// the empty string represents the local dependent encoding
 		static iconv_t iconv_handle = iconv_open("", "UTF-8");
 		if (iconv_handle == iconv_t(-1)) return s;
@@ -674,6 +679,10 @@ namespace libtorrent
 
 	std::string convert_from_native(std::string const& s)
 	{
+		static mutex iconv_mutex;
+		// only one thread can use this handle at a time
+		mutex::scoped_lock l(iconv_mutex);
+
 		// the empty string represents the local dependent encoding
 		static iconv_t iconv_handle = iconv_open("UTF-8", "");
 		if (iconv_handle == iconv_t(-1)) return s;