信号处理

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-------------------------------------------------------------------------信号处理概说  送出信号  接收信号  信号的处理 

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任务控制  -------------------------------------------------------------------------POSIX IPC  reliable/unreliable  reentrant 

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pending  sending signals  catching signals  manipulating  signal definitions 

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-------------------------------------------------------------------------信号singals 信号的处理可以用一大章来写，涉及的层面也会深入整个作业系统中，我并不打算这样做，因为您可能会越搞越迷糊。这里我只告诉您如何接上信号，在实用的层面上，这样便很够用了。您可以先利用这些基本的技巧来撰写程式，等到有进一步高等应用的需要时，找一本较深入的UNIX Programming教材，专门研究signal的写法。  一般简单的signal写法如下:  void mysignal(int signo) 

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{    /* my signal handler */  }  void initsignal(void)  { 

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  struct sigaction act;    act.sa_handler = mysignal;    act.sa_flags   = 0;    sigemptyset(&act.sa_mask);    sigaction(SIGHUP,&act,NULL); 

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  sigaction(SIGINT,&act,NULL);    sigaction(SIGQUIT,&act,NULL);    sigaction(SIGILL,&act,NULL);    sigaction(SIGTERM,&act,NULL);  }    

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例一: lock.c 在fork的例三中提到，在daemon被杀掉时，需要在离开前，将/var/run/lock.pid删除。这里我们可以利用signal来处理这件事。  #include   #include   #include  

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#include   #define LOCK_FILE  "/var/run/lock.pid "  void quit(int signo)  { 

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  printf( "Receive signal %d ",signo);    unlink(LOCK_FILE);    exit(1);  }  void main(void) 

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{    FILE *fp;    pid_t pid;    struct sigaction act;    if (access(LOCK_FILE,R_OK)==0) { 

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    printf( "Existing a copy of this daemon! ");      exit(1);    }    pid = fork(); 

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  if (pid>0) {      printf( "daemon on duty! ");      fp = fopen(LOCK_FILE, "wt ");      fprintf(fp, "%d ",pid);      fclose(fp); 

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  } else      exit(0);  if (pid<0) {      printf( "Can 't fork! ");      exit(-1);    } 

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  act.sa_handler = quit;    act.sa_flags   = 0;    sigemptyset(&act.sa_mask);    sigaction(SIGTERM,&act,NULL);    sigaction(SIGHUP,&act,NULL);    sigaction(SIGINT,&act,NULL); 

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  sigaction(SIGQUIT,&act,NULL);    sigaction(SIGUSR1,&act,NULL);    sigaction(SIGUSR2,&act,NULL);    for (;;) {      sleep(3); 

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  }  }  编译: gcc -o ex1 lock.c  执行

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./ex1  daemon on duty!  送信号 我们先找出该守护神程式的pid  PID=`cat /var/run/lock.pid` 

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接下来利用kill来送信号  kill $PID  Receive signal 15 

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程式将会结束，并且/var/run/lock.pid将会被删除掉，以便下一次daemon再启动。注意到如果quit函数内，没有放exit()，程式将永远杀不掉。  接下来送一些其它的信号试试看。  ./ex1  PID=`cat /var/run/lock.pid` 

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kill -HUP $PID  Receive signal 1  您可以自行试试  kill -INT $PID 

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kill -QUIT $PID  kill -ILL $PID  .  .  .  等等这些信号，看看他们的结果如何。 

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信号的定义 在/usr/include/signum.h中有各种信号的定义  #define SIGHUP          1 &nb 

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