cancellation file support for bluebox

src/prover_slow.h

@@ -108,7 +108,8 @@ std::vector<uint8_t> ProveSlow(integer& D, form& x, uint64_t num_iterations, std
             if (shutdown_file_path!="") {
                 struct stat buffer;
 
-                if (stat (shutdown_file_path.c_str(), &buffer) != 0) {
+                int statrst = stat(shutdown_file_path.c_str(), &buffer);
+                if ((statrst != 0) && (statrst != EINTR)) {
                     // shutdown file doesn't exist, abort out
                     return {};
                 }