2 @page tevent_data Chapter 3: Accessing data
3 @section data Accessing data with tevent
5 A tevent request is (usually) created together with a structure for storing the
6 data necessary for an asynchronous computation. For these private data, tevent
7 library uses void (generic) pointers, therefore any data type can be very
8 simply pointed at. However, this attitude requires clear and guaranteed
9 knowledge of the data type that will be handled, in advance. Private data can
10 be of 2 types: connected with a request itself or given as an individual
11 argument to a callback. It is necessary to differentiate these types, because
12 there is a slightly different method of data access for each. There are two
13 possibilities how to access data that is given as an argument directly to a
14 callback. The difference lies in the pointer that is returned. In one case it
15 is the data type specified in the function’s argument, in another void* is
19 void tevent_req_callback_data (struct tevent_req *req, #type)
20 void tevent_req_callback_data_void (struct tevent_req *req)
24 To obtain data that are strictly bound to a request, this function is the only
28 void *tevent_req_data (struct tevent_req *req, #type)
31 Example with both calls which differs between private data within tevent
32 request and data handed over as an argument.
48 static void foo_done(struct tevent_req *req) {
50 struct foo_state *a = tevent_req_data(req, struct foo_state);
53 struct testA *b = tevent_req_callback_data(req, struct testA);
56 struct testA *c = (struct testA *)tevent_req_callback_data_void(req);
58 printf("a->x: %d\n", a->x);
59 printf("b->y: %d\n", b->y);
60 printf("c->y: %d\n", c->y);
64 struct tevent_req * foo_send(TALLOC_CTX *mem_ctx, struct tevent_context *event_ctx) {
67 struct tevent_req *req;
68 struct foo_state *state;
70 req = tevent_req_create(event_ctx, &state, struct foo_state);
76 static void run(struct tevent_context *ev, struct tevent_timer *te,
77 struct timeval current_time, void *private_data) {
78 struct tevent_req *req;
79 struct testA *tmp = talloc(ev, struct testA);
81 req = foo_send(ev, ev);
83 tevent_req_set_callback(req, foo_done, tmp);
88 int main (int argc, char **argv) {
90 struct tevent_context *event_ctx;
93 struct tevent_timer *time_event;
95 mem_ctx = talloc_new(NULL); //parent
99 event_ctx = tevent_context_init(mem_ctx);
100 if (event_ctx == NULL)
103 data = talloc(mem_ctx, struct testA);
106 time_event = tevent_add_timer(event_ctx,
108 tevent_timeval_current(),
111 if (time_event == NULL) {
112 fprintf(stderr, " FAILED\n");
116 tevent_loop_once(event_ctx);
118 talloc_free(mem_ctx);
125 Output of this example is: