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Margo
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Add code for lecture demonstrations.
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9 files changed

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‎shell3/GNUmakefile

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ALLPROG=share own pipe pipe1 pipe2 pipe3 pipeline
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all: $(ALLPROG)
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O ?= -O2
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include ../common/rules.mk
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%: %.o $(BUILDSTAMP)
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$(CC) $(LDFLAGS) -o $@ $<
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%.o: %.c $(BUILDSTAMP)
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$(CC) $(CPPFLAGS) $(CFLAGS) $(DEPCFLAGS) $(O) -o $@ -c $<
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clean:
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rm -f $(ALLPROG) *.o
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rm -rf $(DEPSDIR) *.dSYM
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.PHONY: all clean

‎shell3/data.out

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PARENTPARENTchildPARENTchildPARENTchildPARENTchildPARENTchildPARENTPARENTPARENTPARENTchildchildchildchildchild

‎shell3/own.c

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#include <sys/stat.h>
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#include <sys/types.h>
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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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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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// We want the parent and child to each have their own file descriptor.
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// So, we will create the file in the parent and then close it; then
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// we'll open it after the fork.
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int fd = open("data.out", O_CREAT | O_WRONLY, 0644);
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if (fd < 0)
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exit(1);
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close(fd);
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pid_t p = fork();
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fd = open("data.out", O_WRONLY, 0644);
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if (p == 0) {
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// Child
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const char *buf = "child";
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ssize_t len = (ssize_t)strlen(buf);
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for (int i = 0; i < 10; i++) {
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if (write(fd, buf, strlen(buf)) != len)
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exit(1);
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usleep(1);
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}
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} else if (p > 0) {
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// Parent
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const char *buf = "PARENT";
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ssize_t len = (ssize_t)strlen(buf);
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for (int i = 0; i < 10; i++) {
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if (write(fd, buf, strlen(buf)) != len)
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exit(1);
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usleep(1);
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}
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} else
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printf("Fork failed!\n");
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}

‎shell3/pipe.c

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#include <sys/stat.h>
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#include <sys/types.h>
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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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// Pipe from parent to child without proper pipe hygiene
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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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// We want to establish a pipe between the parent and child
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// so we have to create the pipe (and therefore open its file
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// descriptors) before forking.
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int pipefd[2];
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if (pipe(pipefd) != 0)
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exit(1);
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// We now have two open file descriptors that our processes will use
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pid_t p = fork();
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pid_t mypid = getpid();
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if (p == 0) {
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// Child: We want the parent to write to the child, so
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// that means the child will be the reader.
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char buf[1];
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printf("Child(%d): ", mypid);
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while (read(pipefd[0], buf, 1) > 0)
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printf("%c", buf[0]);
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printf("\n");
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} else if (p > 0) {
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// Parent -- will be writer
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printf("Parent(%d)\n", mypid);
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char *buf = "Message from parent to child\n";
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ssize_t len = (ssize_t)strlen(buf);
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if (write(pipefd[1], buf, len) != len)
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exit(1);
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// Close pipe
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close(pipefd[1]);
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} else
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printf("Fork failed!\n");
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}

‎shell3/pipe1.c

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#include <sys/stat.h>
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#include <sys/types.h>
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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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// In this one, we close the write end of the pipe in the child
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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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// We want to establish a pipe between the parent and child
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// so we have to create the pipe (and therefore open its file
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// descriptors) before forking.
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int pipefd[2];
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if (pipe(pipefd) != 0)
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exit(1);
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// We now have two open file descriptors that our processes will use
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pid_t p = fork();
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pid_t mypid = getpid();
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if (p == 0) {
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close(pipefd[1]);
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// Child: We want the parent to write to the child, so
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// that means the child will be the reader.
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char buf[1];
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printf("Child(%d): ", mypid);
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while (read(pipefd[0], buf, 1) > 0)
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printf("%c", buf[0]);
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printf("\n");
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} else if (p > 0) {
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// Parent -- will be writer
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printf("Parent(%d)\n", mypid);
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char *buf = "Message from parent to child\n";
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ssize_t len = (ssize_t)strlen(buf);
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if (write(pipefd[1], buf, len) != len)
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exit(1);
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// Close pipe
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close(pipefd[1]);
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} else
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printf("Fork failed!\n");
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printf("%d exiting\n", mypid);
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}

‎shell3/pipe2.c

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#include <sys/stat.h>
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#include <sys/types.h>
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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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// In this one, we close the write end of the pipe in the child
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// In this one, we close the extra read end too AND we make the pipe
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// connect stdout to stdin.
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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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// We want to establish a pipe between the parent and child
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// so we have to create the pipe (and therefore open its file
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// descriptors) before forking.
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int pipefd[2];
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if (pipe(pipefd) != 0)
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exit(1);
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// We now have two open file descriptors that our processes will use
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pid_t p = fork();
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pid_t mypid = getpid();
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if (p == 0) {
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close(pipefd[1]);
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// Child: We want the parent to write to the child, so
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// that means the child will be the reader.
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// This makes the pipe read end be the child's stdin,
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// closing all the extra file descriptors.
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dup2(pipefd[0], STDIN_FILENO);
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close(pipefd[0]);
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char buf[1];
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printf("Child(%d): ", mypid);
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while (read(STDIN_FILENO, buf, 1) > 0)
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printf("%c", buf[0]);
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printf("\n");
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} else if (p > 0) {
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close(pipefd[0]);
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printf("Parent(%d)\n", mypid);
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// Parent -- will be writer
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// This makes the pipe write end be the parent's stdout,
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// closing the old stdout and the extra fd from the pipe.
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dup2(pipefd[1], STDOUT_FILENO);
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close(pipefd[1]);
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char *buf = "Message from parent to child\n";
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ssize_t len = (ssize_t)strlen(buf);
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if (write(STDOUT_FILENO, buf, len) != len)
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exit(1);
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} else
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printf("Fork failed!\n");
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printf("%d exiting\n", mypid);
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}

‎shell3/pipe3.c

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#include <sys/stat.h>
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#include <sys/types.h>
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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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// In this one, we demonsrate proper pipe hygiene, but use printf/scanf
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// to make it obvious that we're redirecting stdin/stdout.
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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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// We want to establish a pipe between the parent and child
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// so we have to create the pipe (and therefore open its file
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// descriptors) before forking.
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int pipefd[2];
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if (pipe(pipefd) != 0)
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exit(1);
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// We now have two open file descriptors that our processes will use
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pid_t p = fork();
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pid_t mypid = getpid();
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if (p == 0) {
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printf("Child(%d): ", mypid);
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close(pipefd[1]);
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// Child: We want the parent to write to the child, so
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// that means the child will be the reader.
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// This makes the pipe read end be the child's stdin,
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// closing the old stdin and the extra pipefd.
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dup2(pipefd[0], STDIN_FILENO);
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close(pipefd[0]);
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char buf[1024];
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if (scanf("%s", buf) != 1)
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printf("Scanf failed\n");
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printf("Child read %s\n", buf);
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} else if (p > 0) {
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printf("Parent(%d)\n", mypid);
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close(pipefd[0]);
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// Parent -- will be writer
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// This makes the pipe write end be the parent's stdout,
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// closing the old stdout.
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dup2(pipefd[1], STDOUT_FILENO);
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close(pipefd[1]);
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printf("Message-from-parent-to-child\n");
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} else
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printf("Fork failed!\n");
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printf("%d exiting\n", mypid);
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}

‎shell3/pipeline.c

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#include <sys/stat.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <assert.h>
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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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// We will create a pipe between two child processes by creating the
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// following pipeline: ls | cat.
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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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int pipefd[2];
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if (pipe(pipefd) != 0)
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exit(1);
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// Fork off first child -- its STDOUT should be the write end of
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// the pipe.
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pid_t p1 = fork();
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if (p1 == 0) {
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// We are in the first child; we can close off the read end
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// of the pipe.
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close(pipefd[0]);
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// Next, let's hook up our standard out to the pipe, and
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// close extra fds.
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dup2(pipefd[1], STDOUT_FILENO);
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close(pipefd[1]);
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// Now, let's exec ls
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char *cargv[] = {"ls", 0};
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execvp("ls", cargv);
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printf("If this ever prints something bad happened\n");
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}
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// We aren't the child, so let's make sure we didn't error
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assert(p1 > 0);
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pid_t p2 = fork();
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if (p2 == 0) {
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// We are in the second child; let's close off the write
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// end of the pipe.
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close(pipefd[1]);
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// Now let's hook up our standard in to the pipe and
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// close extra fds.
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dup2(pipefd[0], STDIN_FILENO);
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close(pipefd[0]);
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// Now we should be able to exec sort
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char *cargv[] = {"sort", 0};
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execvp("sort", cargv);
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printf("If we get here the second exec failed\n");
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}
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assert(p2 > 0);
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// We are the parent; let's close the pipe
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close(pipefd[0]);
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close(pipefd[1]);
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// Now let's wait for the second child
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int status;
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waitpid(p2, &status, 0);
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}

‎shell3/share.c

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#include <sys/stat.h>
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#include <sys/types.h>
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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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int main(int argc, char *argv[]) {
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(void)argc;
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(void)argv;
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// We want the parent and child to share the file descriptor
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// so we are going to open it BEFORE forking
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int fd = open("data.out", O_CREAT | O_WRONLY, 0644);
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if (fd < 0)
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exit(1);
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pid_t p = fork();
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if (p == 0) {
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// Child
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const char *buf = "child";
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ssize_t len = (ssize_t)strlen(buf);
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for (int i = 0; i < 10; i++) {
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if (write(fd, buf, strlen(buf)) != len)
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exit(1);
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usleep(1);
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}
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} else if (p > 0) {
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// Parent
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const char *buf = "PARENT";
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ssize_t len = (ssize_t)strlen(buf);
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for (int i = 0; i < 10; i++) {
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if (write(fd, buf, strlen(buf)) != len)
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exit(1);
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usleep(1);
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}
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} else
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printf("Fork failed!\n");
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}

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