Philip Silva via 9fans <9fans@9fans.net> once said:
> if ((cpid = fork()) != 0) {
> close(infd[1]);
> close(outfd[1]);
>
> n = write(infd[0], "test", 4);
> printf("check process: wrote %d bytes\n", n);
>
> sendnote(cpid);
> // close(infd[0]); // <--- uncomment to make write fail
> // close(outfd[0]);
>
> n = write(infd[0], "test2", 5);
> printf("write: wrote %d bytes\n", n);
>
> n = read(outfd[0], outbuf, 20);
> printf("outbuf=%s (n=%d)\n", outbuf, n);
> wait();
> return 0;
Why aren't you waiting for the process to die
after sending it the note? It must be running
to see that is has a note pending. At the time
of your second write, the scheduler may not
have selected the child process to run.
The sequence could look like:
child: read from empty pipe, go to sleep
parent: write to pipe
parent: write kill to /proc/$cpid/note
parent: write to pipe
child: wakeup, see note, die
Cheers,
Anthony
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