258 lines
7.6 KiB
C
258 lines
7.6 KiB
C
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/*
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* task54.c — 子进程管理程序
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*
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* 借鉴 sigmask.c 的信号掩码方法管理子进程:
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* 1. 在操作子进程列表时阻塞 SIGCHLD, 防止信号处理程序并发修改
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* 2. 通过 sigwait / signal handler 等待子进程终止
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*
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* 支持命令:
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* create <n> 创建 n 个子进程, 显示各子进程 PID
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* kill <P1> ... 终止指定 PID 的子进程, 子进程打印 "killed by parent" 后退出
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* ps -u 显示当前存活子进程列表
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* exit 等待所有子进程结束后退出父进程
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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 <signal.h>
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#include <sys/wait.h>
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#include <errno.h>
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#define MAX_CHILDREN 1024
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#define MAX_LINE 256
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/* 子进程 PID 列表, 受 SIGCHLD 信号保护 */
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static pid_t child_pids[MAX_CHILDREN];
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static int child_count = 0;
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/* ---------- SIGCHLD 信号处理程序 ---------- */
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static void sigchld_handler(int sig)
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{
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int saved_errno = errno;
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pid_t pid;
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int status;
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/* 回收所有已终止的子进程, 不阻塞 */
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while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
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printf("[SIGCHLD] 子进程 %d 已终止", pid);
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if (WIFEXITED(status))
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printf(", 退出码=%d", WEXITSTATUS(status));
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if (WIFSIGNALED(status))
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printf(", 被信号 %d (%s) 终止", WTERMSIG(status),
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(WTERMSIG(status) == SIGTERM) ? "SIGTERM" : "");
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printf("\n");
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/* 从列表中移除该 PID */
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for (int i = 0; i < child_count; i++) {
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if (child_pids[i] == pid) {
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child_pids[i] = child_pids[child_count - 1];
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child_count--;
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break;
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}
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}
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}
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errno = saved_errno;
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}
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/* ---------- 子进程执行的代码 ---------- */
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static void child_main(void)
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{
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/* 安装 SIGTERM 处理: 打印消息后退出 */
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struct sigaction sa;
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memset(&sa, 0, sizeof(sa));
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sa.sa_handler = SIG_DFL; /* 先恢复默认以便后续操作 */
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sigemptyset(&sa.sa_mask);
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/* 子进程: 等待 SIGTERM 信号后打印信息并退出 */
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sigset_t mask;
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sigemptyset(&mask);
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sigaddset(&mask, SIGTERM);
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sigprocmask(SIG_BLOCK, &mask, NULL); /* 阻塞 SIGTERM, 用 sigwait 同步等待 */
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int sig;
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sigwait(&mask, &sig); /* 等待 SIGTERM */
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printf("killed by parent\n");
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exit(100);
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}
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/* ---------- 创建子进程 ---------- */
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static void cmd_create(int n)
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{
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sigset_t block_mask, old_mask;
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/* 阻塞 SIGCHLD, 防止 handler 并发修改 child_pids */
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sigemptyset(&block_mask);
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sigaddset(&block_mask, SIGCHLD);
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sigprocmask(SIG_BLOCK, &block_mask, &old_mask);
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int created = 0;
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for (int i = 0; i < n; i++) {
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if (child_count >= MAX_CHILDREN) {
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printf("子进程数已达上限 %d\n", MAX_CHILDREN);
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break;
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}
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pid_t pid = fork();
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if (pid < 0) {
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perror("fork");
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break;
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}
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if (pid == 0) {
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/* 子进程: 恢复默认信号掩码, 执行子进程代码 */
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sigprocmask(SIG_SETMASK, &old_mask, NULL);
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child_main();
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/* child_main 不会返回 */
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}
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/* 父进程: 记录子进程 PID */
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child_pids[child_count++] = pid;
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created++;
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}
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/* 恢复信号掩码 */
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sigprocmask(SIG_SETMASK, &old_mask, NULL);
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if (created > 0) {
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printf("已创建 %d 个子进程:", created);
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/* 新创建的 PID 在列表末尾 */
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for (int i = child_count - created; i < child_count; i++)
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printf(" %d", child_pids[i]);
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printf("\n");
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}
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}
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/* ---------- 终止指定子进程 ---------- */
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static void cmd_kill(int n, pid_t *pids)
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{
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for (int i = 0; i < n; i++) {
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/* 检查 PID 是否在管理列表中 */
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int found = 0;
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for (int j = 0; j < child_count; j++) {
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if (child_pids[j] == pids[i]) {
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found = 1;
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break;
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}
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}
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if (!found) {
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printf("PID %d 不是当前管理的子进程, 跳过\n", pids[i]);
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continue;
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}
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/* 发送 SIGTERM, 子进程的 sigwait 会捕获并处理 */
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if (kill(pids[i], SIGTERM) == 0) {
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printf("已向子进程 %d 发送终止信号\n", pids[i]);
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} else {
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perror("kill");
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}
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}
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/* SIGCHLD handler 会自动回收并清理列表 */
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}
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/* ---------- 显示当前子进程列表 ---------- */
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static void cmd_ps(void)
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{
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sigset_t block_mask, old_mask;
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/* 阻塞 SIGCHLD, 安全读取列表 */
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sigemptyset(&block_mask);
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sigaddset(&block_mask, SIGCHLD);
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sigprocmask(SIG_BLOCK, &block_mask, &old_mask);
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if (child_count == 0) {
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printf("当前无子进程\n");
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} else {
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printf("当前子进程 (%d 个):", child_count);
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for (int i = 0; i < child_count; i++)
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printf(" %d", child_pids[i]);
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printf("\n");
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}
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sigprocmask(SIG_SETMASK, &old_mask, NULL);
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}
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/* ---------- 命令行解析与执行 ---------- */
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static void process_command(char *line)
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{
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/* 去掉末尾换行符 */
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size_t len = strlen(line);
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if (len > 0 && line[len - 1] == '\n') line[len - 1] = '\0';
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if (len == 0) return;
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/* 提取第一个 token */
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char *cmd = strtok(line, " ");
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if (!cmd) return;
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if (strcmp(cmd, "create") == 0) {
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char *arg = strtok(NULL, " ");
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if (!arg) { printf("用法: create <进程数>\n"); return; }
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int n = atoi(arg);
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if (n <= 0) { printf("进程数必须为正整数\n"); return; }
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cmd_create(n);
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} else if (strcmp(cmd, "kill") == 0) {
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pid_t pids[256];
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int n = 0;
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char *arg;
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while ((arg = strtok(NULL, " ")) && n < 256)
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pids[n++] = atoi(arg);
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if (n == 0) { printf("用法: kill <P1> <P2> ...\n"); return; }
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cmd_kill(n, pids);
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} else if (strcmp(cmd, "ps") == 0) {
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char *arg = strtok(NULL, " ");
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if (!arg || strcmp(arg, "-u") != 0) {
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printf("用法: ps -u\n");
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return;
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}
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cmd_ps();
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} else if (strcmp(cmd, "exit") == 0) {
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/* 检查是否还有子进程存活 */
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sigset_t block_mask, old_mask;
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sigemptyset(&block_mask);
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sigaddset(&block_mask, SIGCHLD);
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sigprocmask(SIG_BLOCK, &block_mask, &old_mask);
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int remaining = child_count;
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sigprocmask(SIG_SETMASK, &old_mask, NULL);
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if (remaining > 0) {
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printf("还有 %d 个子进程未终止, 请先 kill 或等待其结束\n", remaining);
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return;
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}
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printf("所有子进程已结束, 父进程退出\n");
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exit(0);
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} else {
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printf("未知命令: %s\n", cmd);
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printf("支持: create <n> | kill <P1> ... | ps -u | exit\n");
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}
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}
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int main(void)
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{
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/* 安装 SIGCHLD 处理程序 */
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struct sigaction sa;
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memset(&sa, 0, sizeof(sa));
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sa.sa_handler = sigchld_handler;
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sigemptyset(&sa.sa_mask);
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sa.sa_flags = SA_NOCLDSTOP | SA_RESTART; /* 仅在子进程终止时通知, 自动重启慢速系统调用 */
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sigaction(SIGCHLD, &sa, NULL);
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/* 忽略 SIGTERM, 父进程不会被意外终止 */
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signal(SIGTERM, SIG_IGN);
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printf("=== 子进程管理程序 ===\n");
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printf("命令: create <n> | kill <P1> <P2> ... | ps -u | exit\n");
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char line[MAX_LINE];
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while (1) {
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printf("> ");
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fflush(stdout);
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if (!fgets(line, sizeof(line), stdin)) break; /* EOF */
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process_command(line);
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}
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printf("\n父进程退出\n");
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return 0;
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}
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