你好，我正在制作一个简单的外壳。当用户单击控件 Z 时，我想简单地切换仅前台模式的状态。当用户单击控件 C 时，我只想终止前台进程（后台子进程应该忽略它）。
如果我运行 shell 并发送“ls”或“sleep 10”等命令，它们就会起作用。这样做后，如果我按控制 C 或 Z，这也有效。只有在发送控制 C 或 Z 后，正常命令才会停止工作。例如，在命令 C 之后发送“ls”将不会执行。为什么是这样？信号与 STDIN 是否混乱？
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现在使用 sigaction 我可以正确处理命令 C 信号。然而尝试控制 Z 会导致叉子炸弹。我怎样才能防止这种情况发生。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <dirent.h>
#include <limits.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
int last_exit_status = 0;
int last_termination = 0;
int backgroundChildrenRunning = 0;
int backgroundPid = 0;
int ignoreBackground = 0;
void child_sigint_handler(int signum) {
//nothing here for now
}
void child_sigint_handlerSec(int signum) {
//do nothing here for background process
}
void sigint_handler(int signum) {// Signal handler for SIGINT (Ctrl-C)
//nothing here now
}
void sigtstp_handler(int signum) {// Signal handler for SIGTSTP
//nothing here for now
}
void check_background() {
if (backgroundChildrenRunning > 0) { //this function is to print the background process termination signal
int currentStatus;
int completedChild = waitpid(-1, ¤tStatus, WNOHANG); //use WHOHANG so it does not block
if (completedChild > 0) {
if (WIFEXITED(currentStatus)) {
printf("Background process with ID %d has been completed. Exit value: %d.\n", completedChild, WEXITSTATUS(currentStatus));
last_termination = WEXITSTATUS(currentStatus);
}
else {
if (completedChild == backgroundPid) {
printf("Background process with ID %d has been completed. Terminated by signal: %d.\n", completedChild, WTERMSIG(currentStatus));
last_termination = WTERMSIG(currentStatus);
}
}
backgroundPid = 0;
backgroundChildrenRunning -= 1;
}
}
}
char* prompt(int pid);
//main func
int main() {
int x = 0;
char *token;
char *argv[1024]; // Array to store command and arguments
int i = 0;
struct sigaction sa;
sa.sa_flags = SA_RESTART;
sa.sa_handler = sigint_handler;
sigaction(SIGINT, &sa, NULL);
struct sigaction sa_tstp;
sa_tstp.sa_handler = sigtstp_handler;
sigaction(SIGTSTP, &sa_tstp, NULL);
while(x == 0) {
check_background();
int pid = getpid();
char* command = prompt(pid); //get user input
if (command != NULL) {
int childExitMethod;
pid_t spwanPID = fork();
token = strtok(command, " "); // Split the command into tokens
while (token != NULL) {//add in all tokens into arr
argv[i] = token;
token = strtok(NULL, " ");
i++;
}
argv[i] = NULL;
int hasSymbolEnd = 0;
if (strcmp(argv[i - 1], "&") == 0){ //checks to see if background or foreground process
if (ignoreBackground == 0) {
hasSymbolEnd = 1;
}
argv[i - 1] = NULL; // Remove the '&' symbol
}
switch (spwanPID){
case -1:
last_exit_status = 1;
case 0:
if (hasSymbolEnd == 1) {
backgroundPid = getpid();
sa.sa_handler = child_sigint_handlerSec;
} else {
sa.sa_handler = child_sigint_handler;
}
execvp(argv[0], argv);
last_exit_status = 1;
exit(1);
default:
if (hasSymbolEnd == 0){
waitpid(spwanPID, &childExitMethod, 0); // Wait for the child only if background
if (WIFEXITED(childExitMethod) && !WEXITSTATUS(childExitMethod)) {
last_exit_status = 0;
} else if (!WIFSIGNALED(childExitMethod)){
printf("bash: %s: command not found\n", command);
last_exit_status = 1;
}
if (WIFSIGNALED(childExitMethod)) { //Check if the child was terminated by a signal
int terminatedBySignal = WTERMSIG(childExitMethod);
printf("Terminated by signal %d\n", terminatedBySignal);
}
} else {
printf("background pid is %d\n", spwanPID);
backgroundChildrenRunning += 1;
}
}
}
}
return 0;
}
char* prompt(int pid) {
printf("%d:", pid);
fflush(stdout);
char* input = NULL;
size_t input_size = 0;
ssize_t read_bytes = getline(&input, &input_size, stdin);// Use getline to read user input
if (read_bytes == -1) {
free(input); // Free the memory
return NULL;
}
if (input[read_bytes - 1] == '\n') {// Remove the newline character at the end
input[read_bytes - 1] = '\0';
}
return input;
}
关于 SIGINT 处理，您可以：
对于 SIGTSTP 处理，请在
sigtstp_handler// rest of your includes and global variables
void sigint_handler(int signum) {
// Main shell should ignore SIGINT
}
void sigtstp_handler(int signum) {
ignoreBackground = !ignoreBackground; // Toggle the state
}
// rest of your functions
int main() {
// rest of your main function
struct sigaction sa_ignore;
sa_ignore.sa_handler = SIG_IGN; // Ignore signal
sigaction(SIGINT, &sa_ignore, NULL);
struct sigaction sa_tstp;
sa_tstp.sa_handler = sigtstp_handler; // Handle SIGTSTP
sigaction(SIGTSTP, &sa_tstp, NULL);
// rest of your main function
switch (spwanPID) {
// rest of your switch case
case 0:
// Child process
if (hasSymbolEnd == 1) {
// Background process should ignore SIGINT
sigaction(SIGINT, &sa_ignore, NULL);
} else {
// Foreground process should handle SIGINT
struct sigaction sa_child;
sa_child.sa_handler = SIG_DFL; // Default signal handling
sigaction(SIGINT, &sa_child, NULL);
}
execvp(argv0, argv);
// rest of your case 0
}
// rest of your main function
}
你会得到，对于你的fork过程：
User Input
|
v
Shell Loop
|
+---> Fork Process
| |
| +---> Execute Command (ls, sleep)
| | |
| | +---> SIGINT Handling (Child)
| |
| +---> SIGINT Ignored (Background Child)
|
+---> SIGINT Ignored (Main Shell)
|
+---> SIGTSTP Toggles Foreground Mode (Main Shell)