Im using the low-level C xpc api <xpc/xpc.h> and i get this error when I run it: Underlying connection interrupted. I know this error stems from the call to xpc_session_send_message_with_reply_sync(session, message, &reply_err);. I have no previous experience with xpc or dispatch and I find the xpc docs very limited and I also found next to no code examples online. Can somebody take a look at my code and tell me what I did wrong and how to fix it? Thank you in advance. Main code: #include <stdio.h> #include <xpc/xpc.h> #include <dispatch/dispatch.h> // the context passed to mainf() struct context { char* text; xpc_session_t sess; }; // This is for later implementation and the name is also rudimentary void mainf(void* c) { //char * text = ((struct context*)c)->text; xpc_session_t session = ((struct context*)c)->sess; dispatch_queue_t messageq = dispatch_queue_create("y.ddd.main", DISPATCH_QUEUE_SERIAL); xpc_object_t message = xpc_dictionary_create(NULL, NULL, 0); xpc_dictionary_set_string(message, "test", "eeeee"); if (session == NULL) { printf("Session is NULL\n"); exit(1); } __block xpc_rich_error_t reply_err = NULL; __block xpc_object_t reply; dispatch_sync(messageq, ^{ reply = xpc_session_send_message_with_reply_sync(session, message, &reply_err); if (reply_err != NULL) printf("Reply Error: %s\n", xpc_rich_error_copy_description(reply_err)); }); if (reply != NULL) printf("Reply: %s\n", xpc_dictionary_get_string(reply, "test")); else printf("Reply is NULL\n"); } int main(int argc, char* argv[]) { // Create seperate queue for mainf() dispatch_queue_t mainq = dispatch_queue_create("y.ddd.main", DISPATCH_QUEUE_CONCURRENT); dispatch_queue_t xpcq = dispatch_queue_create("y.ddd.xpc", NULL); // Create the context being sent to mainf struct context* c = malloc(sizeof(struct context)); c->text = malloc(sizeof("Hello")); strcpy(c->text, "Hello"); xpc_rich_error_t sess_err = NULL; xpc_session_t session = xpc_session_create_xpc_service("y.getFilec", xpcq, XPC_SESSION_CREATE_INACTIVE, &sess_err); if (sess_err != NULL) { printf("Session Create Error: %s\n", xpc_rich_error_copy_description(sess_err)); xpc_release(sess_err); exit(1); } xpc_release(sess_err); xpc_session_set_incoming_message_handler(session, ^(xpc_object_t message) { printf("message recieved\n"); }); c->sess = session; xpc_rich_error_t sess_ac_err = NULL; xpc_session_activate(session, &sess_ac_err); if (sess_err != NULL) { printf("Session Activate Error: %s\n", xpc_rich_error_copy_description(sess_ac_err)); xpc_release(sess_ac_err); exit(1); } xpc_release(sess_ac_err); xpc_retain(session); dispatch_async_f(mainq, (void*)c, mainf); xpc_release(session); dispatch_main(); } XPC Service code: #include <stdio.h> #include <xpc/xpc.h> #include <dispatch/dispatch.h> int main(void) { xpc_rich_error_t lis_err = NULL; xpc_listener_t listener = xpc_listener_create("y.getFilec", NULL, XPC_LISTENER_CREATE_INACTIVE, ^(xpc_session_t sess){ printf("Incoming Session: %s\n", xpc_session_copy_description(sess)); xpc_session_set_incoming_message_handler(sess, ^(xpc_object_t mess) { xpc_object_t repl = xpc_dictionary_create_empty(); xpc_dictionary_set_string(repl, "test", "test"); xpc_rich_error_t send_repl_err = xpc_session_send_message(sess, repl); if (send_repl_err != NULL) printf("Send Reply Error: %s\n", xpc_rich_error_copy_description(send_repl_err)); }); xpc_rich_error_t sess_ac_err = NULL; xpc_session_activate(sess, &sess_ac_err); if (sess_ac_err != NULL) printf("Session Activate: %s\n", xpc_rich_error_copy_description(sess_ac_err)); }, &lis_err); if (lis_err != NULL) { printf("Listener Error: %s\n", xpc_rich_error_copy_description(lis_err)); xpc_release(lis_err); } xpc_rich_error_t lis_ac_err = NULL; xpc_listener_activate(listener, &lis_ac_err); if (lis_ac_err != NULL) { printf("Listener Activate Error: %s\n", xpc_rich_error_copy_description(lis_ac_err)); xpc_release(lis_ac_err); } dispatch_main(); }