Add concurrency check to rpc mining to ensure not too many threads. number of cores times 4 or 257.

src/rpc/core_rpc_server.cpp

@@ -616,6 +616,23 @@ namespace cryptonote
       return true;
     }
 
+    unsigned int concurrency_count = boost::thread::hardware_concurrency() * 4;
+
+    // if we couldn't detect threads, set it to a ridiculously high number
+    if(concurrency_count == 0)
+    {
+      concurrency_count = 257;
+    }
+
+    // if there are more threads requested than the hardware supports
+    // then we fail and log that.
+    if(req.threads_count > concurrency_count)
+    {
+      res.status = "Failed, too many threads relative to CPU cores.";
+      LOG_PRINT_L0(res.status);
+      return true;
+    }
+
     boost::thread::attributes attrs;
     attrs.set_stack_size(THREAD_STACK_SIZE);