1. optimization: avoid global queue if the next sandbox has the same deadline with the current sandbox. 2. correct format and enrich comments

runtime/Makefile

@@ -58,6 +58,7 @@ BINARY_NAME=sledgert
 # CFLAGS += -DLOG_REQUEST_ALLOCATION
 # CFLAGS += -DLOG_PREEMPTION
 # CFLAGS += -DLOG_MODULE_LOADING
+# CFLAGS += -DOPT_AVOID_GLOBAL_QUEUE
 
 # This dumps per module *.csv files containing the cycle a sandbox has been in RUNNING when each
 # page is allocated. This helps understand the relationship to memory allocation and execution time.

runtime/include/sandbox_request.h

@@ -25,7 +25,7 @@ struct sandbox_request {
 	uint64_t        absolute_deadline;         /* cycles */
 	char * 		previous_function_output;
 	ssize_t 	output_length;
-	ssize_t previous_request_length;                    /* previous request length */
+	ssize_t 	previous_request_length;
 	/*
 	 * Unitless estimate of the instantaneous fraction of system capacity required to run the request
 	 * Calculated by estimated execution time (cycles) * runtime_admissions_granularity / relative deadline (cycles)

runtime/include/worker_thread_execute_epoll_loop.h

@@ -24,6 +24,7 @@ worker_thread_execute_epoll_loop(void)
 		struct epoll_event epoll_events[RUNTIME_MAX_EPOLL_EVENTS];
 		int                descriptor_count = epoll_wait(worker_thread_epoll_file_descriptor, epoll_events,
                                                   RUNTIME_MAX_EPOLL_EVENTS, 0);
+
 		if (descriptor_count < 0) {
 			if (errno == EINTR) continue;
 

runtime/src/current_sandbox.c

@@ -70,6 +70,10 @@ current_sandbox_start(void)
 	sandbox_initialize_stdio(sandbox);
 	struct module * next_module = sandbox->module->next_module;
 
+	/* 
+	 * Add the client fd to epoll if it is the first or last sandbox in the chain because they 
+	 * need to read and write from/to this fd
+	 */
 	if (sandbox->request_from_outside || next_module == NULL) {
 		sandbox_open_http(sandbox);
 	}
@@ -78,10 +82,12 @@ current_sandbox_start(void)
 		if (sandbox_receive_request(sandbox) < 0) { 
 			error_message = "Unable to receive or parse client request\n";
 			goto err;
-		};
+		}
 	} else {
-		/* copy previous output to sandbox->request_response_data, as the input for the current sandbox.*/
+		/* 
-		/* let sandbox->http_request->body points to sandbox->request_response_data*/
+		 * Copy previous output to sandbox->request_response_data, as the input for the current sandbox.
+		 * Let sandbox->http_request->body points to sandbox->request_response_data
+		 */
 		assert(sandbox->previous_function_output != NULL);
 		memcpy(sandbox->request_response_data, sandbox->previous_function_output, sandbox->output_length);
 		sandbox->http_request.body 		= sandbox->request_response_data;
@@ -107,7 +113,12 @@ current_sandbox_start(void)
 	if (next_module != NULL) {
 		/* Generate a new request, copy the current sandbox's output to the next request's buffer, and put it to the global queue */
 		ssize_t output_length = sandbox->request_response_data_length - sandbox->request_length;
-		char * pre_func_output = (char *) malloc(output_length);
+		char * pre_func_output = (char *)malloc(output_length);
+		if (!pre_func_output) {
+                	fprintf(stderr, "Failed to allocate memory for the previous output: %s\n", strerror(errno));
+                	goto err;
+        	};
+
 		memcpy(pre_func_output, sandbox->request_response_data + sandbox->request_length, output_length);
 	 	uint64_t enqueue_timestamp = __getcycles();	
 		struct sandbox_request *sandbox_request =
@@ -116,11 +127,31 @@ current_sandbox_start(void)
                                                            (const struct sockaddr *)&sandbox->client_address,
                                                            sandbox->request_arrival_timestamp, enqueue_timestamp, 
 							   true, pre_func_output, output_length);
-		/* TODO: all sandboxs in the chain share the same request id, but sandbox_request_allocate() will busy-wait to generate an unique
+		/* TODO: All sandboxs in the chain share the same request id, but sandbox_request_allocate() 
-		   id, should we optimize it here?*/
+		 *	 will busy-wait to generate an unique id, should we optimize it here?
+		 */
 		sandbox_request->id = sandbox->id; 
+#ifdef OPT_AVOID_GLOBAL_QUEUE
+		/* TODO: The running time of the current sandbox contains the next sandbox's initialization time, does it matter? */
+		if (sandbox->absolute_deadline == sandbox_request->absolute_deadline) { 
+			/* Put the next sandbox to the local run queue to reduce the overhead of the global queue */
+			struct sandbox *next_sandbox = sandbox_allocate(sandbox_request);
+                	if (!next_sandbox) {
+				free(sandbox_request);
+				goto err;
+			}
+
+                	assert(next_sandbox->state == SANDBOX_INITIALIZED);
+                	sandbox_set_as_runnable(next_sandbox, SANDBOX_INITIALIZED);
+		} else {
 			/* Add to the Global Sandbox Request Scheduler */
                 	global_request_scheduler_add(sandbox_request);
+		}
+#else 
+		/* Add to the Global Sandbox Request Scheduler */
+		global_request_scheduler_add(sandbox_request);
+#endif
+		/* Remove the client fd from epoll if it is the first sandbox in the chain */
 		if (sandbox->request_from_outside) {
 			sandbox_remove_from_epoll(sandbox);
 		}

runtime/src/global_request_scheduler_minheap.c

@@ -75,7 +75,8 @@ sandbox_request_get_priority_fn(void *element)
  * Initializes the variant and registers against the polymorphic interface
  */
 void
-global_request_scheduler_minheap_initialize() {
+global_request_scheduler_minheap_initialize() 
+{
 	global_request_scheduler_minheap = priority_queue_initialize(4096, true, sandbox_request_get_priority_fn);
 
 	struct global_request_scheduler_config config = {

runtime/src/module.c

@@ -559,14 +559,9 @@ module_new_from_json(char *file_name)
 			
 			assert(module);
 
-			if (tail_module == NULL) {
+			if (tail_module != NULL) { tail_module->next_module = module; }
 			tail_module			= module;
 			tail_module->next_module 	= NULL;
-			} else {
-				tail_module->next_module = module;
-				tail_module = module;
-				tail_module->next_module = NULL;
-			}
 			
 			module_set_http_info(module, request_count, request_headers, request_content_type,
 			                     response_count, reponse_headers, response_content_type);