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From: Anthony Martin <ality@pbrane.org>
To: 9fans <9fans@9fans.net>
Subject: [9fans] Re: Pipes staying after sending note
Date: Sat, 8 Jul 2023 17:03:59 -0700	[thread overview]
Message-ID: <ZKn5b4s7yTJONYTD@alice> (raw)
In-Reply-To: <abToz2TrFbB_rDZLToX8KYmdmHCsdFYT4ZADL09J-GIQHz_IwpO_zPS65WI0SAxidGFcDtMn0_wHe3a7Bq3rbugbMz5SKyjXyxCMAOOr9t0=@protonmail.com>

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


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Permalink: https://9fans.topicbox.com/groups/9fans/T3392001a02ee7ec8-Mfe03d0d140063db1ea509f2a
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      reply	other threads:[~2023-07-09  0:04 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-08 15:46 [9fans] " Philip Silva via 9fans
2023-07-09  0:03 ` Anthony Martin [this message]

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