我正在尝试制作一个程序suspends它的执行直到信号到达。然后,信号到达后我只想我的代码从原来的地方继续执行。我不希望它执行函数处理程序或任何其他内容。有没有一种简单的方法可以做到这一点?我已经奋斗了一周左右,到处阅读,但没有设法获得完全可操作的代码。
特别是,我希望主程序创建一个线程等待某些特定事件发生(例如,用户已将一些数据输入到标准输入)。与此同时,主程序正在做某事,但在某个时候它会暂停执行,直到收到信号。
The signal可能来自线程,因为它已检测到event或者可能是由于timeout因为我不想让它永远等待。
我已经编写了一些代码,但它没有按预期工作......
/*
* This code SHOULD start a thread that gets messages from stdin.
* If the message is a "quit", the thread exits. Otherwise it raises
* a signal that should be caught by the main program.
* The main program simply waits for the message unless a timer of
* 5.5 seconds expires before receiving the signal from the thread.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/time.h>
#include <signal.h>
#define BSIZE 100 /* Buffer size */
sigset_t mask;
pthread_t tid;
//struct itimerval timervalue;
int milisec = 5500; /* Timeout: 5,5 seconds */
int end = 0;
char buffer[BSIZE];
//Function prototypes
void init(void);
void * thread_job(void *);
void message_rcvd(void);
void wait_for_message_or_timeout(void);
int start_timer(struct itimerval, int);
int stop_timer(struct itimerval);
void on_signal(int);
// MAIN: Wait for message or timeout
int main(int argc, char ** argv) {
init();
while(!end){
wait_for_message_or_timeout();
if(!end)
printf("Message received [%s]\n", buffer);
}
return 0;
}
// INIT: Initializes the signals that the program will wait for
// and creates a thread that will eventually generate a signal
void init()
{
/* Init the signals I want to wait for with sigwait() */
sigemptyset(&mask);
sigaddset(&mask, SIGUSR1);
sigaddset(&mask, SIGALRM);
sigprocmask(SIG_BLOCK, &mask, NULL);
//signal(SIGUSR1, SIG_IGN);
signal(SIGUSR1, on_signal);
/* Create the thread and put it to work */
pthread_t tid;
pthread_create(&tid, NULL, thread_job, NULL);
}
void on_signal(int signum){
printf("on_signal\n");
}
// THREAD CODE -------------
// THREAD JOB: When the user inputs a message, it passes the message
// to the main thread by invoking message_rcvd()
void * thread_job(){
int end = 0;
while(!end){
printf("Input message:");
if (fgets(buffer, BSIZE, stdin) != NULL)
message_rcvd();
}
}
// MESSAGE RECEIVED: If message is not equal to "quit" raise a signal
void message_rcvd(){
if(strcmp(buffer, "quit") == 0){
exit(0);
}else{
printf("Going to raise SIGUSR1...");
if(raise(SIGUSR1) == 0)
printf("raised!\n");
}
}
// WAIT: Should wait for signal SIGUSR1 for some time
void wait_for_message_or_timeout(){
int sigid;
struct itimerval t;
/* Set a timer to prevent waiting for ever*/
printf("Setting timer...\n");
start_timer(t, milisec);
/* Put the process to wait until signal arrives */
sigwait(&mask, &sigid);
switch(sigid){
case SIGUSR1:
printf("Received SIGUSR1: Message avaible!\n");
break;
case SIGALRM:
printf("Received SIGALRM: Timeout\n");
end = 1;
break;
default:
printf("Unknown signal received\n");
break;
}
printf("Stopping timer...\n");
/* Stop timer */
stop_timer(t);
}
// START TIMER: I don't want the timer to cause the execution
// of a handler function
int start_timer(struct itimerval timervalue, int msec)
//int start_timer(int msec)
{
timervalue.it_interval.tv_sec = msec / 1000;
timervalue.it_interval.tv_usec = (msec % 1000) * 1000;
timervalue.it_value.tv_sec = msec / 1000;
timervalue.it_value.tv_usec = (msec % 1000) * 1000;
if(setitimer(ITIMER_REAL, &timervalue, NULL))
{
printf("\nsetitimer() error\n");
return(-1);
}
return(0);
}
// STOP TIMER:
int stop_timer(struct itimerval timervalue)
//int stop_timer()
{
timervalue.it_interval.tv_sec = 0;
timervalue.it_interval.tv_usec = 0;
timervalue.it_value.tv_sec = 0;
timervalue.it_value.tv_usec = 0;
if(setitimer(ITIMER_REAL, &timervalue, NULL))
{
printf("\nsetitimer() error\n");
return(-1);
}
return(0);
}
这是此代码的典型执行。
./signaltest
Setting timer...
Input message:hello
Going to raise SIGUSR1...raised!
Input message:friend
Going to raise SIGUSR1...raised!
Input message:Received SIGALRM: Timeout
Stopping timer...
正如您所看到的,信号 SIGUSR1 正在被引发,并且 sigwait 正在被解除阻塞。但是,在发出信号后,代码似乎不再继续。 (请注意,我不需要信号处理程序,但我只是出于调试目的添加了信号处理程序。我已使用以下命令阻止了它的执行sigprocmask
)
为什么 SIGUSR1 解除了 sigwait 的阻塞,但执行不从那里继续?有什么办法可以让解封后继续使用吗?这似乎适用于 SIGALRM,但为什么不适用于 SIGUSR1?
正如我所说,我一直在查看大量的 stackoverflow 问题、在线指南,尝试使用不同的系统调用(例如,暂停、sigsuspend),...但找不到解决此问题的方法:-(
如果您想知道为什么我不通过不使用线程来更简单地执行此代码,是因为这实际上不是我正在实现的代码,而只是一个更简单的示例,以使我的问题更清楚。我实际上正在尝试实现一个网络协议 API,类似于我自己的协议的套接字 API。
提前致谢