fork 后子进程无法正常工作

Question

我正在尝试将主表达式传递给 3 个子表达式。每个子项都会修改表达式，在第三个子项完成后，表达式返回到主函数并打印在屏幕上。

我已经单独运行了每个 child ，并且似乎工作得很好。但是当我在 main 中尝试 execlp 时，出现了问题。

每个子进程在文件( channel )充满数据后读取，然后删除 channel 的内容。

int main(int argc, char* argv[]){
    char expr_buffer[MAX_CHAR + 1];
    int rmv,i;
    int fd1,fd2,fd3,fd4, expr_len, sync;
    ssize_t bytes_written, bytes_read;
    off_t offset;

do{



fd1 = open("Channel_1.txt", O_RDWR | O_CREAT, NULL );
if (fd1 < 0){
    perror("Error opening \"Channel_1.txt\".\n");
    return(1);
}

fd2 = open("Channel_2.txt", O_RDWR | O_CREAT, NULL );
if (fd2 < 0){
    perror("Error opening \"Channel_2.txt\".\n");
    return(1);
}

fd3 = open("Channel_3.txt", O_RDWR | O_CREAT, NULL );
if (fd3 < 0){
    perror("Error opening \"Channel_3.txt\".\n");
    return(1);
}

fd4 = open("Channel_4.txt", O_RDWR | O_CREAT, NULL );
if (fd4 < 0){
    perror("Error opening \"Channel_4.txt\".\n");
    return(1);
}



char formatstring[13];

printf("Waiting for expression...\n");
sprintf(formatstring,"%%%ds",MAX_CHAR);
scanf(formatstring, expr_buffer );

for(i=0; i<MAX_CHAR + 1; i++){
    if ((expr_buffer[i] == '\0') && (i != MAX_CHAR)){
        expr_buffer[i] ='\n';
        expr_buffer[i+1] = '\0';
        break;
    }   
    else if((expr_buffer[i] == '\0') && (i == MAX_CHAR)){
        expr_buffer[i-1]= '\n';
        break;
    }

}

expr_len = strlen(expr_buffer);
struct stat file_stat;
off_t file_size;

int pid_1, pid_2, pid_3;
int status_1, status_2, status_3;

if (ftruncate(fd1, (off_t)0) == -1){
    perror("Error erasing content of file: \"Channel_1.txt\".\n");
    return -1;
}

bytes_written = write(fd1, expr_buffer, expr_len*sizeof(char));

if (bytes_written < 0) {
    perror("Error writing to file: \"Channel_1.txt\"");
    if (close(fd1) < 0) {
        perror(NULL);
    }
    return 1;
}
if (bytes_written < expr_len) {
    printf("Incomplete data written to file: \"Channel_1.txt\".\n");
}   
sync = fsync(fd1);
if (sync == 0){
    printf("Data written successfully to file: \"Channel_1.txt\".\n");
}
else {
    perror("Error syncing data to disk.\n");
    return(-2);//
}


if (!(pid_1 = fork())) {
    printf("trying to execute Child_1\n");
    execlp("./Child_1","Channel_1.txt","Channel_2.txt", NULL );
    perror("execlp");
    return(1);
}
waitpid(pid_1,&status_1,0);
if (WIFEXITED(status_1)) {
    printf("child returned %d\n", WEXITSTATUS(status_1));
}
else {
    printf("child_1 terminated abnormally\n");
} 

if (!(pid_2=fork())) {
    printf("trying to execute Child_2\n");
    execlp("./Child_2", "Channel_2.txt","Channel_3.txt", NULL );
    perror("execlp");
    return(1);
}

waitpid(pid_2,&status_2,0);
if (WIFEXITED(status_2)) {
    printf("child returned %d\n", WEXITSTATUS(status_2));
}
else {
    printf("child_2 terminated abnormally\n");
} 

if (!(pid_3 = fork())) {
    printf("trying to execute Child_3\n");
    execlp("./Child_3", "Channel_3.txt","Channel_4.txt",NULL);
    perror("execlp");
    return(1);
}

waitpid(pid_3,&status_3,0);
if (WIFEXITED(status_3)) {
    printf("child returned %d\n", WEXITSTATUS(status_3));
}
else {
    printf("child_3 terminated abnormally\n");
} 

while(1){


    if (fstat(fd4, &file_stat) == -1) {
        perror("Fstat.");
        return(-1);
    }

    file_size = file_stat.st_size;
    if (file_size == 0){
        printf("\"Channel_4.txt\" is  empty.\n");
    }
    else{
        break;
    }
}

bytes_read = read(fd4, expr_buffer, MAX_CHAR*sizeof(char));
if (bytes_read < 0) {
    perror("Read failure for file: \"Channel_4.txt\"\n");
    close(fd1);
    return 1;
}
printf("%s\n",expr_buffer);

if (close(fd1) < 0) {
    perror(NULL);
    return 2;//
}
if (close(fd2) < 0) {
    perror(NULL);
    return 2;//
}
if (close(fd3) < 0) {
    perror(NULL);
    return 2;//
}
if (close(fd4) < 0) {
    perror(NULL);
    return 2;//
}

}while(expr_buffer[0] != 'q');  


rmv = remove("Channel_1.txt");
if (rmv == -1){
    perror("Error removing Channel_1.txt.\n");
}
rmv = remove("Channel_2.txt");
if (rmv == -1){
    perror("Error removing Channel_2.txt.\n");
}
rmv = remove("Channel_3.txt");
if (rmv == -1){
    perror("Error removing Channel_3.txt.\n");
}
rmv = remove("Channel_4.txt");
if (rmv == -1){
    perror("Error removing Channel_4.txt.\n");
}

return(0);

}

这是 child_1 的一部分

int main(int argc, char *argv[]){
    int expr_len;
    int fd5,fd2,i,j,k;
    off_t offset;
    int bytes_read,bytes_written;
    char expr_buffer[MAX_CHAR +1];
    //elegxos ean grafthkan ta arxeia
    struct stat file_stat;
    off_t file_size;
    int sync;

sleep(1);
fd5 = open(argv[1], O_RDWR | O_CREAT, NULL );
if (fd5 < 0){
    perror("Error opening \"Channel_1.txt\".\n");
    return(1);
}
fd2 = open(argv[2], O_RDWR | O_CREAT, NULL );
if (fd5 < 0){
    perror("Error opening \"Channel_2.txt\".\n");
    return(1);
}
while(1){


    if (fstat(fd5, &file_stat) == -1) {
        perror("Fstat.");
        return(-1);
    }

    file_size = file_stat.st_size;
    if (file_size == 0){
        printf("\"Channel_1.txt\" is  empty.\n");
    }
    else{
        break;
    }
}



offset = lseek(fd5, (off_t)(0*sizeof(char)), SEEK_SET);
if( lseek(fd5, 0*sizeof(char), SEEK_SET) < 0) { 
    printf("%d\n", errno);
        perror("lseek to beginning of file: \"Channel_1.txt\"\n");
        close(fd5);
        return 1;
}
bytes_read = read(fd5, expr_buffer, MAX_CHAR*sizeof(char)); 
if (bytes_read < 0) {
    perror("Read failure for file: \"Channel_1.txt\"\n");
    close(fd5);
    return 1;
}

当我执行程序时，它说 Channel_1.txt 是空的，没有编辑。

Answer 1

纯粹回答您的具体问题，而不解决代码中的任何其他问题:当输入文件 Channel_1.txt 为空时，Child_1 中的代码路径没有return 语句或退出 while(1) 循环的任何其他方式。