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POParent process and child process synchronization
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copied!<p>I have a project that requires me to use signal and fork to read content of a file and write it back to the stdout (low level I/O). I should split the work of reading and writing between parent and child process, and I should begin the parent process first to read and write the content of the file. After the parent finish, I should send signal SIGUSR1 to the child process so it can begin to read and write the next block of data. My reading and writing part runs ok, but I have problem with the signal and process parts. When I run my program, it display the correct output but it never terminates. Could somebody check what is wrong with my code?</p> <p>Here is what I got so far:</p> <pre><code>#define _XOPEN_SOURCE 600 #include <limits.h> /* For LONG_MAX */ #include <fcntl.h> /*For open()*/ #include <unistd.h> /*For close(), read(), write(), nice()*/ #include <stdlib.h> /*For exit()*/ #include <stdio.h> /*For fprintf(),perror()*/ #include <signal.h> /*For signal()*/ #include <sys/types.h> /* For pid_t */ #include <sys/wait.h> /* For wait() */ void my_handler(int); void displayUsage(FILE *, const char *); int main(int argc, char **argv) { char c[BUFSIZ]; /* To hold the string that has been read from the file */ int fd; /* file descriptor */ int n; long int nBytes; /* To hold the number of bytes to read */ pid_t pid; int child_status; /* Display usage if user use this process wrong */ if(argc != 3){ displayUsage(stderr, argv[0]); exit(1); } /* Convert argv[1] to long - number of bytes to read */ nBytes = strtol(argv[1], NULL, 10); if((nBytes <= 0) || (nBytes > INT_MAX)){ fprintf(stderr, "Bufferize %s is not a positive integer\n", argv[1]); exit(2); } /* Open a file */ if((fd = open(argv[2],O_RDONLY,0)) < 0){ perror(argv[2]); exit(3); } /* Attempt to register a signal handler */ if(signal(SIGUSR1, my_handler) == SIG_ERR){ perror("Could not set a handler for SIGUSR1"); exit(4); } /* lowering the process priority */ if(nice(40) < 0){ perror("Cannot lower the priority"); exit(5); } /* Create a new process */ pid = fork(); if(pid < 0){ exit(6); } /* Allocating memory space for string/data to be read from the file if(!(c = malloc(nBytes))){ perror("ERROR"); exit(4); }*/ if(pid == 0){ pause(); /* I'm the child */ printf("Child's turn!\n"); /* Read The File */ while((n = read(fd, c, nBytes)) != 0){ /* Write content of 'c' to the stdout */ if(write(STDOUT_FILENO, c, n) < 0){ perror("Write Error!\n"); exit(7); } } kill(pid,SIGUSR1); } else{ /* I'm the parent */ printf("Parent's turn!\n"); /* Read The File */ while((n = read(fd, c, nBytes)) != 0){ /* Write content of 'c' to the stdout */ if(write(STDOUT_FILENO, c, n) < 0){ perror("Write Error!\n"); exit(7); } } /* Reap the child */ wait(&child_status); kill(pid, SIGUSR1); } pause(); /* Close the file */ if(close(fd) < 0){ perror(argv[2]); exit(8); } exit(0); } void displayUsage(FILE *fp, const char *arg){ fprintf(fp, "Usage: %s n filename\n", arg); fprintf(fp, "where\n"); fprintf(fp, "\tn\tNumber of bytes to read and write in each \"block\".\n"); fprintf(fp,"\tfilename\tName of file to be catted.\n"); } void my_handler(int sig){ /* Re-registering the handler */ if(signal(SIGUSR1, my_handler) == SIG_ERR){ perror("Could not set a handler for SIGUSR1"); exit(4); } /*if(isParent == 1){ printf("Parent's turn!\n"); } else{ printf("Child's turn!\n"); }*/ } </code></pre>

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