【发布时间】：2018-04-20 03:53:10
【问题描述】：
我正在使用 C shell，但无法让任意数量的管道正常工作。当我运行外壳时，它挂在任何管道上。出于某种原因，当我执行ls -la | sort 时，它会挂起，直到我输入内容并点击Ctrl+D。我知道这与管道未关闭有关，但打印语句显示管道 3、4、5 在父级和子级中都已关闭。我已经在这工作了几个小时，不知道为什么这不起作用。任何帮助将不胜感激。
原代码：
char *current_command;
current_command = strtok_r(cmdline_copy, "|", &cmdline_copy);
char *commands[100][MAX_ARGS]; //Max 100 piped commands with each having MAX_ARGS arguments
int i = 0;
while (current_command != NULL) { //Go through each command and add it to the array
char *copy = malloc(strlen(current_command)*sizeof(char)); //Copy of curretn command
strcpy(copy, current_command);
char *args_t[MAX_ARGS];
int nargs_t = get_args(copy, args_t);
memcpy(commands[i], args_t, sizeof(args_t)*nargs_t); //Copy the command and it's arguments to the 2d array
i++;
current_command = strtok_r(NULL, "|\n", &cmdline_copy); //Use reentrant version of strtok to prevent fighting with get_args function
}
int fd[2*(i-1)]; //Set up the pipes i.e fd[0,1] is first pipe, fd[1,2] second pipe, etc.
for (int j = 0; j < i*2; j+=2) {
pipe(fd+j);
}
//Here is where we do the commands
for (int j = 0; j < i; j++) {
pid = fork(); //Fork
if (pid == 0) { //Child process
if (j == 0) { //First process
printf("Child Closed %d\n", fd[0]);
close(fd[0]);
dup2(fd[1], fileno(stdout));
}
else if (j == i -1) { //Last process
dup2(fd[j], fileno(stdin));
printf("Child closed %d\n", fd[j]);
printf("Child closed %d\n", fd[j+1]);
close(fd[j+1]);
close(fd[j]);
}
else { //Middle processes
dup2(fd[j], fileno(stdin));
dup2(fd[j+1], fileno(stdout));
printf("Child closed %d\n", fd[j]);
close(fd[j]);
}
execvp(commands[j][0], commands[j]);
}
else if (pid > 0) { //Parent
printf("Parent closed %d\n", fd[j]);
close(fd[j]);
printf("Parent closed %d\n", fd[j+1]);
close(fd[j+1]);
waitpid(pid, NULL, 0); //Wait for the process
}
else {
perror("Error with fork");
exit(1);
}
}
最终代码：
char *current_command;
current_command = strtok_r(cmdline_copy, "|", &cmdline_copy);
char *commands[100][MAX_ARGS]; //Max 100 piped commands with each having MAX_ARGS arguments
int command_count = 0;
while (current_command != NULL) { //Go through each command and add it to the array
char *copy = malloc(strlen(current_command)*sizeof(char)); //Copy of curretn command because get_args uses strtok
strcpy(copy, current_command);
char *args_t[MAX_ARGS];
int nargs_t = get_args(copy, args_t);
memcpy(commands[command_count], args_t, sizeof(args_t)*nargs_t); //Copy the command and it's arguments to the 2d array
command_count++;
current_command = strtok_r(NULL, "|\n", &cmdline_copy); //Use reentrant version of strtok to prevent fighting with get_args function
}
int fd[command_count*2-1];
pid_t pids[command_count];
for (int j = 0; j < command_count*2; j+=2) { //Open up a pair of pipes for every command
pipe(fd+j);
}
for (int j = 0; j < command_count; j++) {
pids[j] = fork();
if (pids[j] == 0) { //Child process
if (j == 0) { //Duplicate only stdout pipe for first pipe
dup2(fd[1], fileno(stdout));
}
else if (j == (command_count-1)) { //Duplicate only stdin for last pipe
up2(fd[2*(command_count-1)-2], fileno(stdin));
}
else { //Duplicate both stdin and stdout
dup2(fd[2*(j-1)], fileno(stdin));
dup2(fd[2*j+1], fileno(stdout));
}
for (int k = 0; k < j*2; k++) { //Close all fds
close(fd[k]);
}
execvp(commands[j][0], commands[j]); //Exec the command
}
else if (pids[j] < 0) {
perror("Error forking");
}
}
for (int k = 0; k < command_count*2; k++) { //Parent closes all fds
close(fd[k]);
}
waitpid(pids[command_count-1], NULL, 0); //Wait for only the last process;
【问题讨论】：
-
fd数组和两个for循环肯定有问题：第一个循环使用fd中的i*2元素，但第二个循环仅使用i+1元素.至少第二个循环应该有一个j+=2增量。可悲的是现在没有时间进一步看，这只是一个线索， -
那不是因为管道有两个末端吗？对于 2 个命令，您有 4 个管道，2 进 2 出，然后第二个 for 循环遍历这两个命令。
-
在某种程度上，可以编辑问题。一旦你开始得到答案，你应该谨慎地改变问题以使答案无效。通常，这可能意味着从那里单独保留原始代码（除非您修复非关键拼写错误或类似内容），但添加新/修订代码作为编辑。你应该展示一些有缺陷的代码版本——也可以添加工作代码，但不能使用适当的注释。