The problem was in open() (A possible location that I almost neglected).
> *Opening* a FIFO for reading normally blocks until some other process
> opens the same FIFO for writing, and vice versa.
>
Adding a O_NONBLOCK to open() solved the issue. (I should have read the
manual page completely :/ )
On Monday, April 11, 2016 at 3:39:47 PM UTC+2, SSM wrote:
>
> Problem statement : C application waits for input read events on two file
> descriptors(named pipes) and process the data as they arrive (note that
> events can occur in any order irrespective of when I register the handle
> uv_poll_t)
>
> ptr->fd0=open("pipe0", O_RDONLY);
> uv_poll_init(my_default_loop, file0_poll, ptr->fd0);
> uv_poll_start(file0_poll, UV_READABLE, read0_callback);
>
> ptr->fd1 = open ("pipe1", O_RDONLY);
> uv_poll_init(my_default_loop, file1_poll, ptr->fd1);
> uv_poll_start(file1_poll, UV_READABLE, read1_callback);
>
>
>
> I intend to run the callback function as soon an event occurs. However, my
> application executes only if there is data on pipe0 *first* and *then* on
> pipe1. If I first send data to pipe0, read0_callback is not executed
> immediately. However, it executes after there is data on pipe1.
> Additionally, If I reverse the order of registering callbacks, the symptoms
> also reverse.
>
> A small note: Consider pipe0 and then pipe1 as the order of registering
> callbacks. If I try to send data to pipe1 first using > redirection... The
> shell does not return back. for a fifo to work there should also be an
> application reading on the named pipe. So, I suspect my whole application
> is still synchronous. (Other simple examples that I tried before with
> uv_fs_read, uv_fs_open work asynchronously as expected)
>
>
> (I'm sending data to named pipes using echo "X" > pipe0
>
>
> Could anyone please clarify my approach ?
>
>
> Complete code can be found here
> <https://gist.github.com/saisasidhar/3f29aa4cb7c66e59d902c1bc28b1351d#file-example_poll-c>
>
>
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