c - waitpid() 在特定情况下返回未知错误
问题描述
我创建了父进程和子进程。然后从子进程中，我又创建了 3 个大子进程。
从子进程，SIGTERM 被发送到大子进程并等待大子进程使用 waitpid() 终止。
waitpid() 为 3 个大子进程中的一个大子进程返回未知错误。waitpid() 不会为其他 2 个大子进程返回未知错误。
我编译了代码并运行它。然后，我收到了如下消息。
$ ./a.out
shm_create : shmid = 0
main_process
child process pid = 1953
in grand_chile_process2 : pid = 1955
in grand_child_process2-1
g_child_id->pid[0] = 0
g_child_id->pid[1] = 1955
g_child_id->pid[2] = 0
in process2-2
in grand_child_process1 : pid = 1954
in process1-1
g_child_id->pid[0] = 1954
g_child_id->pid[1] = 1955
g_child_id->pid[2] = 0
in process1-2
in grand_child_process3 : pid = 1956
in process3-1
g_child_id->pid[0] = 1954
g_child_id->pid[1] = 1955
g_child_id->pid[2] = 1956
in process3-2
如果我检查正在运行的进程，我会看到如下 5 个进程。
# ps -eLf | grep a.out
user1 1952 1684 1952 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1953 1952 1953 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1954 1953 1954 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1955 1953 1955 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1956 1954 1956 0 1 13:51 pts/2 00:00:00 ./a.out
root 1958 1885 1958 0 1 13:51 pts/4 00:00:00 grep --color=auto a.out
如果我输入“a”，那么我会看到如下错误消息。
a
Terminating...: pid = 1956
error : waitpid (No child processes)
进程列表如下图所示。
# ps -eLf | grep a.out
user1 1952 1684 1952 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1953 1952 1953 0 1 13:51 pts/2 00:00:00 [a.out] <defunct>
user1 1954 1 1954 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1955 1 1955 0 1 13:51 pts/2 00:00:00 ./a.out
user1 1956 1954 1956 0 1 13:51 pts/2 00:00:00 [a.out] <defunct>
root 1960 1885 1960 0 1 13:51 pts/4 00:00:00 grep --color=auto a.out
在这里，如下面的源代码所示，我首先发送 SIGTERM 到 grand_child_process3()，然后在第 218~246 行之间发送 grand_child_process2() 和 grand_child_process1()。
我进行了更改，按照 grand_child_process1()、grand_child_process2() 和 grand_child_process3() 的顺序发送 SIGTERM。
然后，我再次可以看到如下输出。
$ ./a.out
shm_create : shmid = 0
main_process
child process pid = 1985
in grand_chile_process2 : pid = 1987
in grand_child_process2-1
g_child_id->pid[0] = 0
g_child_id->pid[1] = 1987
g_child_id->pid[2] = 0
in process2-2
in grand_child_process1 : pid = 1986
in process1-1
g_child_id->pid[0] = 1986
g_child_id->pid[1] = 1987
g_child_id->pid[2] = 0
in process1-2
in grand_child_process3 : pid = 1988
in process3-1
g_child_id->pid[0] = 1986
g_child_id->pid[1] = 1987
g_child_id->pid[2] = 1988
in process3-2
进程列表如下所示。
# ps -eLf | grep a.out
user1 1984 1684 1984 0 1 14:03 pts/2 00:00:00 ./a.out
user1 1985 1984 1985 0 1 14:03 pts/2 00:00:00 ./a.out
user1 1986 1985 1986 0 1 14:03 pts/2 00:00:00 ./a.out
user1 1987 1985 1987 0 1 14:03 pts/2 00:00:00 ./a.out
user1 1988 1986 1988 0 1 14:03 pts/2 00:00:00 ./a.out
root 1990 1885 1990 0 1 14:03 pts/4 00:00:00 grep --color=auto a.out
然后，再次按下“a”，输出如下所示。
a
Terminating...: pid = 1986
pid = 1986
child process[1986] killed by signal 15 (Terminated)
Terminating...: pid = 1987
pid = 1987
child process[1987] killed by signal 15 (Terminated)
Terminating...: pid = 1988
error : waitpid (No child processes)
然后，进程列表变成了这样。
# ps -eLf | grep a.out
user1 1984 1684 1984 0 1 14:03 pts/2 00:00:00 ./a.out
user1 1985 1984 1985 0 1 14:03 pts/2 00:00:00 [a.out] <defunct>
root 1992 1885 1992 0 1 14:05 pts/4 00:00:00 grep --color=auto a.out
我的问题是为什么 grand_child_process3() 没有正确终止。
如果您发现我做错了什么，请告诉我。这是我正在使用的完整源代码。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <error.h>
#include <errno.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <sys/wait.h>
#define KEY_NUM 1234
pid_t g_child1, g_child2, g_child3;
int shmid;
struct _process_id {
pid_t pid[3];
};
typedef struct _process_id G_CHILD_ID_t;
int shared_memory_create()
{
void *shared_memory;
shmid = shmget((key_t)KEY_NUM, sizeof(G_CHILD_ID_t), IPC_CREAT|0666);
if (shmid == -1)
{
printf("shmget failed\n");
exit(0);
}
printf("shm_create : shmid = %d\n", shmid);
shared_memory = shmat(shmid, NULL, 0);
if (shared_memory == (void *)-1)
{
printf("shmat failed\n");
exit(0);
}
memset(shared_memory, 0x0, sizeof(G_CHILD_ID_t));
if(shmdt(shared_memory) == -1)
{
printf("shmdt failed\n");
exit(0);
}
return 0;
}
int grand_child_process1(void)
{
G_CHILD_ID_t *g_child_id;
void *shared_memory;
int i = 0;
g_child1 = getpid();
printf("in grand_child_process1 : pid = %d\n", g_child1);
shared_memory = shmat(shmid, NULL, 0);
if (shared_memory == (void *)-1)
{
printf("shmat failed\n");
exit(0);
}
g_child_id = (G_CHILD_ID_t *)shared_memory;
g_child_id->pid[0] = g_child1;
printf("in process1-1\n");
for (i = 0 ; i < 3 ; i++)
printf("g_child_id->pid[%d] = %d\n", i, g_child_id->pid[i]);
if(shmdt(shared_memory) == -1)
{
printf("shmdt failed\n");
exit(0);
}
printf("in process1-2\n");
while(1)
{
sleep(1);
}
}
int grand_child_process2(void)
{
G_CHILD_ID_t *g_child_id;
void *shared_memory;
int i = 0;
g_child2 = getpid();
printf("in grand_chile_process2 : pid = %d\n", g_child2);
shared_memory = shmat(shmid, NULL, 0);
if (shared_memory == (void *)-1)
{
printf("shmat failed\n");
exit(0);
}
g_child_id = (G_CHILD_ID_t *)shared_memory;
g_child_id->pid[1] = g_child2;
printf("in grand_child_process2-1\n");
for (i = 0 ; i < 3 ; i++)
printf("g_child_id->pid[%d] = %d\n", i, g_child_id->pid[i]);
if(shmdt(shared_memory) == -1)
{
printf("shmdt failed\n");
exit(0);
}
printf("in process2-2\n");
while(1)
{
sleep(1);
}
}
int grand_child_process3(void)
{
G_CHILD_ID_t *g_child_id;
void *shared_memory;
int i = 0;
g_child3 = getpid();
printf("in grand_child_process3 : pid = %d\n", g_child3);
shared_memory = shmat(shmid, NULL, 0);
if (shared_memory == (void *)-1)
{
printf("shmat failed\n");
exit(0);
}
g_child_id = (G_CHILD_ID_t *)shared_memory;
g_child_id->pid[2] = g_child3;
printf("in process3-1\n");
for (i = 0 ; i < 3 ; i++)
printf("g_child_id->pid[%d] = %d\n", i, g_child_id->pid[i]);
if(shmdt(shared_memory) == -1)
{
printf("shmdt failed\n");
exit(0);
}
printf("in process3-2\n");
while(1)
{
sleep(1);
}
}
void printWaitStatus(pid_t pid, int status)
{
printf("pid = %d\n", pid);
if (WIFEXITED(status))
{
printf("child process[%d] exited, status = %d\n", pid, WEXITSTATUS(status));
}
else if (WIFSIGNALED(status))
{
printf("child process[%d] killed by signal %d (%s)\n", pid, WTERMSIG(status), strsignal(WTERMSIG(status)));
}
else if (WIFSTOPPED(status))
{
printf("child process[%d] stopped by signal %d (%s)\n", pid, WSTOPSIG(status), strsignal(WSTOPSIG(status)));
}
}
int child_process(void)
{
G_CHILD_ID_t *g_child_id;
void *shared_memory;
int wstatus;
int err;
pid_t p1, p2;
char ch;
printf("child process pid = %d\n", getpid());
p1 = fork();
p2 = fork();
if (p1 == 0 && p2 > 0)
{
grand_child_process1();
}
else if (p1 > 0 && p2 == 0)
{
grand_child_process2();
}
else if (p1 == 0 && p2 == 0)
{
grand_child_process3();
}
shared_memory = shmat(shmid, NULL, 0);
if (shared_memory == (void *)-1)
{
printf("shmat failed\n");
exit(0);
}
g_child_id = (G_CHILD_ID_t *)shared_memory;
while (1)
{
ch = (char)getchar();
if (ch == 'a')
{
printf("Terminating...: pid = %d\n", g_child_id->pid[2]);
kill(g_child_id->pid[2], SIGTERM);
err = waitpid(g_child_id->pid[2], &wstatus, WUNTRACED | WCONTINUED);
if (err == -1)
{
printf("error : waitpid (%s)\n", strerror(errno));
exit(EXIT_FAILURE);
}
printWaitStatus(g_child_id->pid[2], wstatus);
printf("Terminating...: pid = %d\n", g_child_id->pid[1]);
kill(g_child_id->pid[1], SIGTERM);
err = waitpid(g_child_id->pid[1], &wstatus, WUNTRACED | WCONTINUED);
if (err == -1)
{
printf("error : waitpid (%s)\n", strerror(errno));
exit(EXIT_FAILURE);
}
printWaitStatus(g_child_id->pid[1], wstatus);
printf("Terminating...: pid = %d\n", g_child_id->pid[0]);
kill(g_child_id->pid[0], SIGTERM);
err = waitpid(g_child_id->pid[0], &wstatus, WUNTRACED | WCONTINUED);
if (err == -1)
{
printf("error : waitpid (%s)\n", strerror(errno));
exit(EXIT_FAILURE);
}
printWaitStatus(g_child_id->pid[0], wstatus);
if(shmdt(shared_memory) == -1)
{
printf("shmdt failed\n");
exit(0);
}
}
else
sleep(1);
}
return 0;
}
int main_process(void)
{
printf("main_process \n");
while (1)
{
sleep(1);
}
}
int main(void)
{
pid_t pid;
shared_memory_create();
pid = fork();
if (pid == 0)
{
child_process();
}
else
{
main_process();
}
}
解决方案
推荐阅读
- javascript - （同构）路由和基于ajax的react组件的后端渲染
- swift - 如何准备 API 响应以在 swift 中与 jsonDecoder 一起使用
- javascript - Particles Js 的画布显示在页面的最底部
- haskell - 使用递归确定子集
- java - 在 ModelAttribute 中收到模型更新现有数据库记录而不是创建新记录
- jquery - 如何从两个不同的选项中获取选定的选项
- javascript - 合并两个具有内部数组属性的对象而不改变反应中的状态
- c# - 如何在 DataGridView 中仅显示特定行
- security - Falcon 传感器无法启动代理
- dialogflow-es - 从意图异步触发实现 webhook？