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Commit 28c5dfe

Browse files
author
Anton Yarkov
committed
Named and nonamed pipes examples.
1 parent ddce52c commit 28c5dfe

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4 files changed

+286
-0
lines changed

4 files changed

+286
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lines changed

‎multithreading/03 - Nonamed_pipes.cpp

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#include <iostream>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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using namespace std;
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struct CmdLine
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{
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char* value;
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char* arguments;
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CmdLine* next;
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};
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// Compilation:
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// g++ "03 - Nonamed_pipes.cpp" -o nonamedpipes
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// Task:
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// Create a program which works just like the command below:
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// $> who | sort | uniq -c | sort -nk1
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void run(CmdLine* command)
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{
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const int numPipes = 3;
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int i = 0;
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pid_t pid;
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// Create all pipes.
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int pipefds[2*numPipes];
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for(i = 0; i < (numPipes); i++)
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{
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if(pipe(pipefds + i*2) < 0)
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{
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printf("Couldn't create pipe %d\n", i + 1);
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exit(EXIT_FAILURE);
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}
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}
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int j = 0;
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while(command)
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{
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pid = fork();
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if(pid == 0)
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{
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//if not last command
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if(command->next)
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{
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if(dup2(pipefds[j + 1], STDOUT_FILENO) < 0)
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{
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perror("dup2");
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exit(EXIT_FAILURE);
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}
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}
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//if not first command && j != 2*numPipes
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if(j != 0 )
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{
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if(dup2(pipefds[j-2], STDIN_FILENO) < 0)
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{
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perror(" dup2");///j-2 0 j+1 1
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exit(EXIT_FAILURE);
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}
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}
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for(i = 0; i < 2*numPipes; i++)
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{
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close(pipefds[i]);
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}
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// Command with or without arguments.
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if (command->arguments == NULL)
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{
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if( execlp(command->value, command->value, NULL) < 0 )
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{
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perror(command->value);
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exit(EXIT_FAILURE);
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}
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}
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else
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{
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if( execlp(command->value, command->value, command->arguments, NULL) < 0 )
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{
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perror(command->value);
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exit(EXIT_FAILURE);
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}
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}
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}
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else if(pid < 0)
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{
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perror("error");
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exit(EXIT_FAILURE);
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}
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command = command->next;
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j+=2;
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}
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/* Parent closes the pipes and wait for children */
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for(i = 0; i < 2 * numPipes; i++)
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{
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close(pipefds[i]);
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}
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int status;
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for(i = 0; i < numPipes + 1; i++)
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{
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wait(&status);
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}
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}
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int main(int argc, char** argv)
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{
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printf("Result of operation is the same like if you type\n$>who | sort | uniq -c | sort -nk1\n");
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char sort[] = "sort";
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char sortArg[] = "-nk1";
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char uniq[] = "uniq";
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char uniqArg[] = "-c";
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char who[] = "who";
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CmdLine command4 = { sort, sortArg, NULL };
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CmdLine command3 = { uniq, uniqArg, &command4 };
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CmdLine command2 = { sort, NULL, &command3 };
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CmdLine command1 = { who, NULL, &command2 };
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run(&command1);
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return 0;
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}
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#define EXIT_FAILURE 1
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// Compilation:
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// gcc "03 - Nonamed_pipes_read_write.c" -o nonamedpipesrw
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// Task:
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// Do write on one end and read on another end.
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void main()
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{
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int fd[2], nbytes;
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pid_t childpid;
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char string[] = "Hello, world!\n";
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char readbuffer[80];
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pipe(fd);
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printf("Process %d creates child\n", getpid());
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if((childpid = fork()) == -1)
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{
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perror("fork");
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exit(EXIT_FAILURE);
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}
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if(childpid == 0)
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{
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/* Child process closes up input side of pipe */
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close(fd[0]);
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/* Send "string" through the output side of pipe */
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write(fd[1], string, (strlen(string)+1));
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printf("Done write in process %d\n", getpid());
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exit(0);
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}
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else
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{
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/* Parent process closes up output side of pipe */
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close(fd[1]);
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/* Read in a string from the pipe */
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nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
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printf("Received string: %s in process %d\n", readbuffer, getpid());
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}
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exit(0);
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}
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#include <stdio.h>
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#include <unistd.h>
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// Compilation:
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// gcc "03 - Nonamed_pipes_wc_logins.c" -o nonamedpipeslogins
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// Task:
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// Create a program which works just like the command
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// $> who | wc -l
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// Help:
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// Create pipe: who -> stdout -> [pfd[1] -> pfd[0]] -> stdin -> wc -l
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void main()
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{
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printf("Result of operation is the same like if you type\n$>who | wc -l\n");
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int pfd[2];
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pipe(pfd);
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if (!fork())
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{
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// Since descriptors are shared between the parent and child,
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// we should always be sure to close the end of pipe we aren't concerned with.
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// On a technical note, the EOF will never be returned
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// if the unnecessary ends of the pipe are not explicitly closed.
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close(STDOUT_FILENO);
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dup2(pfd[1], STDOUT_FILENO);
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close(pfd[1]);
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close(pfd[0]);
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execlp("who", "who", NULL);
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}
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else
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{
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close(STDIN_FILENO);
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dup2(pfd[0], STDIN_FILENO);
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close(pfd[1]);
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close(pfd[0]);
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execlp("wc", "wc", "-l", NULL);
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}
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exit(0);
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}

‎multithreading/04 - Named_pipes.c

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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#define EXIT_FAILURE 1
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// Compilation:
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// gcc "04 - Named_pipes.c" -o namedpipes
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// Task:
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// Create Named Pipe aka FIFO to do write on one end and read on another end.
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void main()
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{
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char * myfifo = "/tmp/myfifo";
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mkfifo(myfifo, 0666);
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pid_t childpid;
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if((childpid = fork()) == -1)
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{
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perror("fork");
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exit(EXIT_FAILURE);
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}
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if(childpid == 0)
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{
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char string[] = "Hello, world!";
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int fd;
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if (fd = open(myfifo, O_WRONLY))
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{
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write(fd, string, (strlen(string)+1));
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close(fd);
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}
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printf("Process %d done write and unlink fifo.\n", getpid());
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unlink(myfifo);
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}
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else
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{
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printf("Process %d creates child %d\n", getpid(), childpid);
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char readbuffer[80];
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int fd;
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if (fd = open(myfifo, O_RDONLY))
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{
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read(fd, readbuffer, 80);
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printf("Process %d received string: %s\n", getpid(), readbuffer);
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close(fd);
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}
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unlink(myfifo);
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}
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exit(0);
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}

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