tevent_loop_wait() never finishes

[Simo]

On 06/24/2013 08:52 AM, Pavel Březina wrote:
> Hi,
> I've run across a problem where I don't have any custom event handlers 
> registered with tevent, but the program gets stuck in tevent_loop_wait().
>
> When I print out the event context, I see there is still one fd 
> handler registered. It is sig_pipe_handler() that is created 
> internally by tevent at tevent_signal.c:254.
>
> (gdb) p dyndns_test_ctx->tctx->ev[0]
> $11 = {ops = 0x3e14a0aca0, fd_events = 0x62c9b0, timer_events = 0x0, 
> immediate_events = 0x0, signal_events = 0x0, additional_data = 
> 0x622890, pipe_fde = 0x62c9b0, pipe_fds = {12, 14}, debug_ops = {debug 
> = 0,
>     context = 0x0}, nesting = {allowed = false, level = 0, hook_fn = 
> 0, hook_private = 0x0}, tracing = {callback = 0, private_data = 0x0}}
>
> (gdb) p dyndns_test_ctx->tctx->ev[0]
> $6 = {ops = 0x3e14a0aca0, fd_events = 0x62c9b0, timer_events = 0x0, 
> immediate_events = 0x0, signal_events = 0x0, additional_data = 
> 0x622890, pipe_fde = 0x62c9b0, pipe_fds = {12, 14}, debug_ops = {debug 
> = 0,
>     context = 0x0}, nesting = {allowed = false, level = 0, hook_fn = 
> 0, hook_private = 0x0}, tracing = {callback = 0, private_data = 0x0}}
>
> What is the purpose of this signal?

It is used to process signal events outside of the actual signal handler 
where the amount of processing and systems call that can be used is limited.
When a signal comes tevent simply writes to the pipe so that as soon as 
control is returned to the event loop it sees that a read is possible on 
the fd and calls the correct code to deal with the reported signal.

> Is there any way how to remove it?

Apparently the only place where this happens is when the event context 
is freed or re-initialized.

> Also why ev->fd_events->prev == ev->fd_events?
I am not sure about this, I do not see where or why this happens.

Simo.