fix bug: negative remaining slack turns to be a large number when assign it to a uint64_t type of value

runtime/include/sandbox_set_as_running.h

@@ -23,13 +23,18 @@ sandbox_set_as_running(struct sandbox *sandbox, sandbox_state_t last_state)
 	case SANDBOX_RUNNABLE: {
 		uint64_t start_execution = now - system_start_timestamp;
 		uint64_t last = sandbox->last_update_timestamp;
-		uint32_t last_rs = sandbox->remaining_slack;
-		sandbox->remaining_slack -= (now - sandbox->last_update_timestamp);
+		uint64_t last_rs = sandbox->remaining_slack;
+		int64_t rs = sandbox->remaining_slack - (now - sandbox->last_update_timestamp);
+		if (rs < 0) {
+			sandbox->remaining_slack = 0;
+		} else {
+			sandbox->remaining_slack = rs;
+		}
 		sandbox->last_update_timestamp = now;  
 		sandbox->runnable_duration += duration_of_last_state;
 		current_sandbox_set(sandbox);
 		runtime_worker_threads_deadline[worker_thread_idx] = sandbox->absolute_deadline;
-                mem_log("time %lu sandbox starts running, request id:%d name %s obj=%p remaining slack %lu, last_rs %u now %lu last %lu \n", start_execution,
+                mem_log("time %lu sandbox starts running, request id:%d name %s obj=%p remaining slack %lu, last_rs %lu now %lu last %lu \n", start_execution,
                          sandbox->id, sandbox->module->name, sandbox, sandbox->remaining_slack, last_rs, now, last);
 		/* Does not handle context switch because the caller knows if we need to use fast or slow switched */
 		break;

runtime/src/listener_thread.c

@@ -182,7 +182,10 @@ listener_thread_main(void *dummy)
                                         next_module = next_module->next_module;
                                 }
 
-                                uint64_t remaining_slack = module->relative_deadline - estimated_execution_time;
+                                int64_t remaining_slack = module->relative_deadline - estimated_execution_time;
+				if (remaining_slack < 0) {
+					remaining_slack = 0;
+				}
 				
 				/* Allocate a Sandbox Request */
 				struct sandbox_request *sandbox_request =