Process 在继续进程之前，将SIGUSR1或SIGINT发送到已停止进程时未捕获信号——为什么？

为什么当您停止一个进程，然后尝试用SIGUSR1或SIGINT终止它时，直到您发送SIGCONT，信号才被捕获？但是当你用SIGKILL终止它时，信号马上就被捕获了

在我们自己的shell中，我们在gdb中遵循了这一点。在继续该过程之前，信号根本不会被捕获。父进程的SIGCHLD处理程序在发送SIGCONT信号后捕捉到它，子进程的WIFSIGNALED（status）返回true（这意味着之前没有捕捉到该信号，对吗？）

常规Linux shell将SIGUSR1发送到已停止的进程：

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4668 pts/2    00:00:00 testing
 4669 pts/2    00:00:00 ps
$ kill -SIGUSR1 4668
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4668 pts/2    00:00:00 testing
 4670 pts/2    00:00:00 ps
$ kill -SIGCONT 4668
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4671 pts/2    00:00:00 ps
[1]+  User defined signal 1   ./testing 30
$ 

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4691 pts/2    00:00:00 testing
 4692 pts/2    00:00:00 ps
$ kill -SIGINT 4691
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4691 pts/2    00:00:00 testing
 4702 pts/2    00:00:00 ps
$ kill -SIGCONT 4691
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4703 pts/2    00:00:00 ps
[1]+  Interrupt               ./testing 30
$

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 5243 pts/2    00:00:00 bash
 5331 pts/2    00:00:00 testing
 5332 pts/2    00:00:00 ps
$ kill -SIGKILL 5331
$ ps
  PID TTY          TIME CMD
 5243 pts/2    00:00:00 bash
 5334 pts/2    00:00:00 ps
[1]+  Killed                  ./testing 30
$

常规Linux shell将SIGINT发送到已停止的进程：

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4668 pts/2    00:00:00 testing
 4669 pts/2    00:00:00 ps
$ kill -SIGUSR1 4668
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4668 pts/2    00:00:00 testing
 4670 pts/2    00:00:00 ps
$ kill -SIGCONT 4668
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4671 pts/2    00:00:00 ps
[1]+  User defined signal 1   ./testing 30
$ 

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4691 pts/2    00:00:00 testing
 4692 pts/2    00:00:00 ps
$ kill -SIGINT 4691
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4691 pts/2    00:00:00 testing
 4702 pts/2    00:00:00 ps
$ kill -SIGCONT 4691
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4703 pts/2    00:00:00 ps
[1]+  Interrupt               ./testing 30
$

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 5243 pts/2    00:00:00 bash
 5331 pts/2    00:00:00 testing
 5332 pts/2    00:00:00 ps
$ kill -SIGKILL 5331
$ ps
  PID TTY          TIME CMD
 5243 pts/2    00:00:00 bash
 5334 pts/2    00:00:00 ps
[1]+  Killed                  ./testing 30
$

常规Linux shell向停止的进程发送SIGKILL：

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4668 pts/2    00:00:00 testing
 4669 pts/2    00:00:00 ps
$ kill -SIGUSR1 4668
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4668 pts/2    00:00:00 testing
 4670 pts/2    00:00:00 ps
$ kill -SIGCONT 4668
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4671 pts/2    00:00:00 ps
[1]+  User defined signal 1   ./testing 30
$ 

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4691 pts/2    00:00:00 testing
 4692 pts/2    00:00:00 ps
$ kill -SIGINT 4691
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4691 pts/2    00:00:00 testing
 4702 pts/2    00:00:00 ps
$ kill -SIGCONT 4691
$ ps
  PID TTY          TIME CMD
 2775 pts/2    00:00:00 bash
 4703 pts/2    00:00:00 ps
[1]+  Interrupt               ./testing 30
$

$ ./testing 30
^Z
[1]+  Stopped                 ./testing 30
$ ps
  PID TTY          TIME CMD
 5243 pts/2    00:00:00 bash
 5331 pts/2    00:00:00 testing
 5332 pts/2    00:00:00 ps
$ kill -SIGKILL 5331
$ ps
  PID TTY          TIME CMD
 5243 pts/2    00:00:00 bash
 5334 pts/2    00:00:00 ps
[1]+  Killed                  ./testing 30
$

---

SIGKILL

无法阻止

SIGUSR1

和

SIGINT

可以。

那么发送SIGTSTP信号会自动阻止它们吗？这取决于代码要求什么。例如，如果您使用

sigaction

，您可以通过设置

sau mask

参数来控制它。（我自己的shell只是为了看看信号在gdb中的位置）如果你不要求任何特殊的东西，你就不会得到任何特殊的东西。所以默认情况下，SIGTSTP会自动阻止这些信号吗？谢谢