Given the following program –
#include <iostream>
#include <uv.h>
int main()
{
uv_loop_t loop;
uv_loop_init(&loop);
std::cout << "Libuv version: " << UV_VERSION_MAJOR << "."
<< UV_VERSION_MINOR << std::endl;
int r = 0;
uv_timer_t t1_handle;
r = uv_timer_init(&loop, &t1_handle);
uv_timer_start(&t1_handle,
[](uv_timer_t *t) { std::cout << "Timer1 calledn"; }, 0, 2000);
uv_run(&loop, UV_RUN_DEFAULT);
// second timer
uv_timer_t t2_handle;
r = uv_timer_init(&loop, &t2_handle);
uv_timer_start(&t2_handle,
[](uv_timer_t *t) { std::cout << "Timer2 calledn"; }, 0, 1000);
uv_loop_close(&loop);
}
The second timer handle is never run on the loop, since the loop is already running, and “Timer2 called” is never printed. So I tried stopping the loop temporarily after running it and then adding the second timer –
.... uv_run(&loop, UV_RUN_DEFAULT); // some work uv_stop(&loop); // now add second timer uv_run(&loop, UV_RUN_DEFAULT); // run again ....
But this again didn’t work, probably because the later lines won’t be executed after 1st loop starts running with an repeating timer. So how should I add a new timer handle to already running uvloop?
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Answer
You are right that loop needs to be stopped before it can register a new handle. It cannot be achieved by calling uv_stop function right after uv_run, because uv_run needs to return first. It can be achieved for example by stopping it using a handle callback. Here is quite silly example of how it can be done using the existing Timer1 handle. It stops the loop exactly one time on the first run.
#include <iostream>
#include <uv.h>
int main() {
uv_loop_t loop;
uv_loop_init(&loop);
std::cout << "Libuv version: " << UV_VERSION_MAJOR << "." << UV_VERSION_MINOR
<< std::endl;
int r = 0;
uv_timer_t t1_handle;
r = uv_timer_init(&loop, &t1_handle);
*(bool *)t1_handle.data = true; // need to stop the loop
uv_timer_start(&t1_handle,
[](uv_timer_t *t) {
std::cout << "Timer1 calledn";
bool to_stop = *(bool *)t->data;
if (to_stop) {
std::cout << "Stopping loop and resetting the flagn";
uv_stop(t->loop);
*(bool *)t->data = false; // do not stop the loop again
}
},
0, 2000);
uv_run(&loop, UV_RUN_DEFAULT);
std::cout << "After uv_runn";
// second timer
uv_timer_t t2_handle;
r = uv_timer_init(&loop, &t2_handle);
uv_timer_start(&t2_handle,
[](uv_timer_t *t) { std::cout << "Timer2 calledn"; }, 0,
1000);
std::cout << "Start loop againn";
uv_run(&loop, UV_RUN_DEFAULT);
uv_loop_close(&loop);
}
So the output is
Libuv version: 1.9 Timer1 called Stopping loop and resetting the flag After uv_run Start loop again Timer2 called Timer2 called Timer1 called Timer2 called Timer2 called Timer1 called