1.进程中每个线程都有自己的信号屏蔽字和信号未决字
2.信号的处理方式是进程中所有线程共享的
3.进程中的信号是递送到单个线程的
4.定时器是进程资源，进程中所有的线程共享共同的定时器
例1：
下面这个例子通过一个子线程调用了alarm函数产生alarm信号，由于信号的处理方式就是进程中所有线程共享的，这个时候也就是说主线程和该子线程都有可能捕获该信号，通过下面的程序可以看出，是主程序捕获了信号。
由于alarm是单次触发，所以在信号处理函数中，又需要重新调用alarm函数，继续触发。
实验源码如下：
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
void sig_handler(int signo)
{
printf("pthread id in the sig_handler: %lx\n",pthread_self());
if(signo==SIGALRM)
{
printf("timeout...\n");
}
alarm(2);
}
void * th_fn(void *arg)
{
if(signal(SIGALRM,sig_handler)==SIG_ERR)
{
perror("signal sigalrm error");
}
alarm(2);
int i;
for(i=1;i<=100;i++)
{
printf("(%lx) i: %d\n",pthread_self(),i);
sleep(1);
}
return (void*)0;
}
int main(void)
{
int err;
pthread_t rabbit;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);
if((err=pthread_create(&rabbit,&attr,th_fn,(void *)0))!=0)
{
perror("pthread_create error");
}
while(1)
{
printf("control thread id: %lx\n",pthread_self());
sleep(10);
}
return 0;
}
主程序里设定了主线程睡10s，但是主线程收到了alarm信号，因此就会被唤醒，所以过2s就会继续运行
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 1
(7f8ffe90c700) i: 2
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 3
(7f8ffe90c700) i: 4
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 5
(7f8ffe90c700) i: 6
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 7
(7f8ffe90c700) i: 8
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 9
(7f8ffe90c700) i: 10
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 11
(7f8ffe90c700) i: 12
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 13
(7f8ffe90c700) i: 14
pthread id in the sig_handler: 7f8fff10f700
timeout...
control thread id: 7f8fff10f700 is running
(7f8ffe90c700) i: 15
(7f8ffe90c700) i: 16
^C
######################################
如果需要主线程不需要捕获信号，可以在主线程里屏蔽即可：
在上述程序中，while(1)语句前，加入以下代码：
sigset_t set;
sigemptyset(&set);
sigaddset(&set,SIGALRM);
pthread_sigmask(SIG_SETMASK,&set,NULL);
其运行结果如下：
control thread id: 7fda2a07d700 is running
(7fda2987a700) i: 1
(7fda2987a700) i: 2
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 3
(7fda2987a700) i: 4
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 5
(7fda2987a700) i: 6
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 7
(7fda2987a700) i: 8
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 9
(7fda2987a700) i: 10
control thread id: 7fda2a07d700 is running
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 11
(7fda2987a700) i: 12
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 13
(7fda2987a700) i: 14
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 15
(7fda2987a700) i: 16
pthread id in the sig_handler: 7fda2987a700
timeout...
(7fda2987a700) i: 17
(7fda2987a700) i: 18
^C
3.如何在一个线程中结束另一个线程，传入另一个线程的标识符，其源码如下：
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
void sig_handler(int signo)
{
printf("pthread id in the sig_handler: %lx\n",pthread_self());
if(signo==SIGALRM)
{
printf("timeout...\n");
}
alarm(2);
}
void * th_fn(void *arg)
{
if(signal(SIGALRM,sig_handler)==SIG_ERR)
{
perror("signal sigalrm error");
}
alarm(2);
int i;
for(i=1;i<=100;i++)
{
printf("1:(%lx) i: %d\n",pthread_self(),i);
sleep(1);
}
return (void*)0;
}
void *th_fn2(void *arg)
{
pthread_t th=(pthread_t) arg;
int i;
for(i=1;i<=100;i++)
{
if(i==5)
{
pthread_cancel(th);
alarm(0);
}
printf("2:(%lx) i: %d\n",pthread_self(),i);
sleep(1);
}
}
int main(void)
{
int err;
pthread_t rabbit,turtle;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);
if((err=pthread_create(&rabbit,&attr,th_fn,(void *)0))!=0)
{
perror("pthread_create error");
}
if((err=pthread_create(&turtle,&attr,th_fn2,(void *)rabbit))!=0)
{
perror("pthread_create error");
}
sigset_t set;
sigemptyset(&set);
sigaddset(&set,SIGALRM);
pthread_sigmask(SIG_SETMASK,&set,NULL);
while(1)
{
printf("control thread id: %lx is running\n",pthread_self());
sleep(10);
}
return 0;
}