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C, Piping messages to child processes not working. Why?


C, Piping messages to child processes not working. Why?

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C, Piping messages to child processes not working. Why?
Tag : c , By : Chris Woods
Date : November 28 2020, 09:01 AM

With these it helps You have undefined behavior in the code. You have an array of pointers to characters msg, and you use this array when reading input from the user.
The first problem here is that the pointers in the array are uninitialized. The value of uninitialized local variables is indeterminate and using them in any way except to initialize them leads to undefined behavior. Either dynamically allocate memory for these pointers, or use an array of arrays of characters, e.g.
char msg[nmessages][MAX_MESSAGE_LENGTH];

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Piping output from two tar processes into a single child


Tag : linux , By : user178709
Date : March 29 2020, 07:55 AM
Hope this helps I can pipe two commands into a single child like so (Edit: actually you can't do it like this, see sarnold answers): , You're doing it wrong (even for the first snippet).
{ tar -x --to-command MySerialiser -f MyData1.tar.xz && tar -x --to-command MySerialiser -f MyData2.tar.xz ; }  | MyAnalyser

Perl as a batch-script tool - fully piping child processes?


Tag : perl , By : Singularity
Date : March 29 2020, 07:55 AM
will be helpful for those in need Apologies if some of the terminology may be slighlty off here. Feel free to correct me if I use a wrong term for something. , Why not this way:
print "Hello, this is a not so simple script.\n";
my $param_x = get_more_complicated_parameter();

system('cmd.exe', $param_x);
my $errorlevel = $? >> 8;
print "The tool returned $errorlevel\n";

sub get_more_complicated_parameter { 42 }

Piping between multiple child processes


Tag : c , By : Patastroph
Date : March 29 2020, 07:55 AM
wish helps you I'm trying to process input through different child process from one parent. I can make it though the first 3 children, but after that, I can't seem to get any input into or anything of out sort. , You seem to have a pipeline:
sed … | tr … | awk … | sort
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

static inline void error(const char *msg)
{
    perror(msg);
    exit(EXIT_FAILURE);
}

int main(void)
{
    int pid;
    int pipes_1[2];
    int pipes_2[2];
    int pipes_3[2];
    pipe(pipes_1);
    pipe(pipes_2);
    pipe(pipes_3);

    if ((pid = fork()) == 0)
    {
        dup2(pipes_1[1], 1);
        close(pipes_1[0]);
        close(pipes_1[1]);
        close(pipes_2[0]);
        close(pipes_2[1]);
        close(pipes_3[0]);
        close(pipes_3[1]);
        execlp("sed", "sed", "s/[^a-zA-Z]/ /g", "test.txt", (char *)NULL);
        error("Failed to exec sed");
    }
    printf("sed:  %d\n", pid);

    if ((pid = fork()) == 0)
    {
        dup2(pipes_1[0], 0);
        dup2(pipes_2[1], 1);
        close(pipes_1[0]);
        close(pipes_1[1]);
        close(pipes_2[0]);
        close(pipes_2[1]);
        close(pipes_3[0]);
        close(pipes_3[1]);
        execlp("tr", "tr", "[A-Z]", "[a-z]", (char *)NULL);
        error("Failed to exec tr");
    }
    printf("tr:   %d\n", pid);

    if ((pid = fork()) == 0)
    {
        dup2(pipes_2[0], 0);
        dup2(pipes_3[1], 1);
        close(pipes_1[0]);
        close(pipes_1[1]);
        close(pipes_2[0]);
        close(pipes_2[1]);
        close(pipes_3[0]);
        close(pipes_3[1]);
        execlp("awk", "awk", "{for(i = 1; i <= NF; i++) {print $i;}}", (char *)NULL);
        error("Failed to exec awk");
    }
    printf("awk:  %d\n", pid);

    if ((pid = fork()) == 0)
    {
        dup2(pipes_3[0], 0);
        close(pipes_1[0]);
        close(pipes_1[1]);
        close(pipes_2[0]);
        close(pipes_2[1]);
        close(pipes_3[0]);
        close(pipes_3[1]);
        execlp("sort", "sort", (char *)NULL);
        error("Failed to exec sort");
    }
    printf("sort: %d\n", pid);

    close(pipes_1[0]);
    close(pipes_1[1]);
    close(pipes_2[0]);
    close(pipes_2[1]);
    close(pipes_3[0]);
    close(pipes_3[1]);

    int status;
    int corpse;
    while ((corpse = wait(&status)) > 0)
        printf("PID %d died 0x%.4X\n", corpse, status);

    return 0;
}
Happy Go Lucky!
PENULTIMATE DESTINY@
missing all upper-case=
What gives?
Digital 023123098 Diarrhea
sed:  74841
tr:   74842
awk:  74843
sort: 74844
PID 74841 died 0x0000
PID 74842 died 0x0000
PID 74843 died 0x0000
all
case
destiny
diarrhea
digital
gives
go
happy
lucky
missing
penultimate
upper
what
PID 74844 died 0x0000

How to create multiple child forks and have multiple messages being sent between child processes and main process


Tag : javascript , By : KT.
Date : March 29 2020, 07:55 AM
seems to work fine Okay so the key is passing the worker number in the worker 'message' because using workers[i-1].send("variable) gives an undefined error:
 for (var i = 1; i <= 2; i++) {                  
    workers.push(childProcess.fork(path.join(__dirname, workerPath)));
    workers[i-1].send("variable");

    workers[i-1].on('message', function(message) {

    workers[message-1].send("variable);
       }); 

Erlang/OTP How to notify parent process that child processes are idle and no messages in their mailbox


Tag : erlang , By : user160048
Date : March 29 2020, 07:55 AM
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