關于linux_unix編程手冊的代碼見
https://github.com/zzu-andrew/linux_unix.git
上面由編譯過得代碼可以直接使用或者自己clone之后再使用

改變信號量的處置

在linux手冊中對函數signal的解釋是：

#include <signal.h>typedef void (*sighandler_t)(int);sighandler_t signal(int signum, sighandler_t handler);

可以看出man手冊對signal的書寫更加的形象，signal返回的是一個 void (*sighandler_t)(int)類型的函數
返回的函數就是之前的信號處理函數，一般使用signal的過程如下：

/*************************************************************************\ * Copyright (C) Michael Kerrisk, 2018. * * * * This program is free software. You may use, modify, and redistribute it * * under the terms of the GNU General Public License as published by the * * Free Software Foundation, either version 3 or (at your option) any * * later version. This program is distributed without any warranty. See * * the file COPYING.gpl-v3 for details. * \*************************************************************************//* Listing 20-1 *//* ouch.cCatch the SIGINT signal, generated by typing control-C (^C).Note that although we use signal() to establish the signal handler in thisprogram, the use of sigaction() is always preferable for this task. */ #include <signal.h> #include "tlpi_hdr.h"static void sigHandler(int sig) {printf("Ouch!\n"); /* UNSAFE (see Section 21.1.2) */ }int main(int argc, char *argv[]) {int j;/* Establish handler for SIGINT. Here we use the simpler signal()API to establish a signal handler, but for the reasons described inSection 22.7 of TLPI, sigaction() is the (strongly) preferred APIfor this task. */if (signal(SIGINT, sigHandler) == SIG_ERR)errExit("signal");/* Loop continuously waiting for signals to be delivered */for (j = 0; ; j++) {printf("%d\n", j);//加上，不然程序不會自己退出，并且使用　　^C ^D他也不能使程序退出if(j == 20){exit(0);}sleep(3); /* Loop slowly... */} }

程序測試過程：

說明，程序中信號處理函數使用printf()函數顯示具體信息，但是在現實的編程環境中是絕對不允許在信號處理函數中使用stdio函數，這里只是將其作為調試的一種手段

為兩個不同的信號建立同樣的信號處理程序：

/*************************************************************************\ * Copyright (C) Michael Kerrisk, 2018. * * * * This program is free software. You may use, modify, and redistribute it * * under the terms of the GNU General Public License as published by the * * Free Software Foundation, either version 3 or (at your option) any * * later version. This program is distributed without any warranty. See * * the file COPYING.gpl-v3 for details. * \*************************************************************************//* Listing 20-2 *//* intquit.cCatch the SIGINT and SIGQUIT signals, which are normally generatedby the control-C (^C) and control-\ (^\) keys respectively.Note that although we use signal() to establish signal handlers in thisprogram, the use of sigaction() is always preferable for this task. */ #include <signal.h> #include "tlpi_hdr.h"static void sigHandler(int sig) {static int count = 0;/* UNSAFE: This handler uses non-async-signal-safe functions(printf(), exit(); see Section 21.1.2) */if (sig == SIGINT) {count++;printf("Caught SIGINT (%d)\n", count);return; /* Resume execution at point of interruption */}/* Must be SIGQUIT - print a message and terminate the process */printf("Caught SIGQUIT - that's all folks!\n");exit(EXIT_SUCCESS); }int main(int argc, char *argv[]) {/* Establish same handler for SIGINT and SIGQUIT. Here we use thesimpler signal() API to establish a signal handler, but for thereasons described in Section 22.7 of TLPI, sigaction() is the(strongly) preferred API for this task. */if (signal(SIGINT, sigHandler) == SIG_ERR)errExit("signal");if (signal(SIGQUIT, sigHandler) == SIG_ERR)errExit("signal");for (;;) /* Loop forever, waiting for signals */pause(); /* Block until a signal is caught */ }

發送信號，使用kill一個進程可以向另一個進程發送信號（之所以使用kill作為術語，是因為早期的UNIX實現中大多數信號的默認行為是終止進程）

#include <signal.h>int kill(pid_t pid, int sig);

pid參數用于標示一個或者多個目標進程，而sig則指向要發送的信號

kill()系統調用還有另一重功用，將參數sig指定為0(即所謂的空信號)，則無信號發送，相反kill()僅會檢查錯誤檢驗，查看是否可以向目標進程發送信號，從另一個角度這意味著，可以使用控信號檢測具有特定進程ID的進程是否存在。若是發送信號失敗，且errno為ESRCH，則表明目標進程不存在，若果調用失敗且errno為EPERM(表示進程存在但是無權向目標進程發送信號)或者調用成功(有權向目標進程發送信號)，那么就表示進程存在。

改變信號處置：sigaction()函數

除去signal()之外，sigaction()系統調用是設置信號好處置的另一個選擇；

等待信號：pause()

調用pause()將暫停進程的執行，直至信號處理器函數中斷該調用為止(或者直至一個為處理的信號終止進程為止)。

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