#include <iostream>
#include <ctime>
#include <cstdio>
#include "errors.h"
#define DEBUG
using namespace std;

typedef struct alarm_tag
{
    struct alarm_tag *link;
    int seconds;
    time_t time;        //seconds from epoch(公元,纪年)
    char message[64];
}alarm_t;

pthread_mutex_t alarm_mutex=PTHREAD_MUTEX_INITIALIZER;
alarm_t *alarm_list=NULL;

//The alarm thread's start routine.
void *alarm_thread(void *arg)
{
    alarm_t *alarm;
    int sleep_time;
    time_t now;
    int status;
        
    while(true)
    {
        status=pthread_mutex_lock(&alarm_mutex);//下面要对数据进行操作，加锁
        if(status!=0)
            err_abort(status,"Lock mutex");
    //    cout<<"thread 2:"<<alarm_list<<endl;
   
        alarm=alarm_list;
        if(alarm==NULL)
            sleep_time=1;
        else
        {
            alarm_list=alarm->link;
            now=time(NULL);
            if(alarm->time<=now)
                sleep_time=0;
            else
                sleep_time=alarm->time-now;
               
            #ifdef DEBUG
                cout<<"waiting: "<<alarm->time<<"("<<sleep_time<<")"<<"'"<<alarm->message<<endl;
            #endif
        }
        
        status=pthread_mutex_unlock(&alarm_mutex);//操作完毕，解锁
        if(status!=0)
            err_abort(status,"Unlock mutex");
        if(sleep_time>0)
            sleep(sleep_time);
        else
            sched_yield();
        
        if(alarm!=NULL)
        {
            cout<<"("<<alarm->seconds<<")"<<alarm->message<<endl;
            free(alarm);
            alarm=NULL;
        }
    }   
}

int main()
{
    int status;
    char line[128];
    alarm_t *alarm,**last,*next;
    pthread_t thread;
   
    status=pthread_create(&thread,NULL,alarm_thread,NULL);
    if(status!=0)
        err_abort(status,"Create alarm thread");
   
    while(true)
    {
        cout<<"alarm> ";
        if(fgets(line,sizeof(line),stdin)==NULL)
            exit(0);
        if(strlen(line)<=1)
            continue;
   
        alarm=(alarm_t*)malloc(sizeof(alarm_t));//申请
        
        if(alarm==NULL)
            errno_abort("Allocate alarm");
   
        if(sscanf(line,"%d %64[^\n]",&alarm->seconds,alarm->message)<2)
        {
            fprintf(stderr,"Bad command\n");
            free(alarm);
            alarm=NULL;
        }
        else
        {
            status=pthread_mutex_lock(&alarm_mutex);//要操作数据，加锁
            if(status!=0)
                err_abort(status,"Lock mutex");
            
            alarm->time=time(NULL)+alarm->seconds;
            //cout<<"thread 1:"<<alarm_list<<endl;
            last=&alarm_list;        //last存放的 alarm_list的地址，alarm_list的内容为空
            next=*last;                //next指向当前结点也就是alarm_list的内容，第一次内容为空
            cout<<"next:"<<next<<endl;
            while(next!=NULL)
            {
                if(next->time>=alarm->time)
                {
                    alarm->link=next;
                    *last=alarm;
                    break;
                }
                last=&next->link;
                next=next->link;
            }
        
            if(next==NULL)
            {
                *last=alarm;
                alarm->link=NULL;
            }
        
            #ifdef DEBUG
                cout<<"List: ";
                for(next=alarm_list;next!=NULL;next=next->link)
                    cout<<"next->time:"<<next->time<<"("<<next->time-time(NULL)<<")"<<
                                                "[---"<<next->message<<"---]"<<endl;
            #endif
            
            status=pthread_mutex_unlock(&alarm_mutex);//操作完毕，解锁  
            if(status!=0)
                err_abort(status,"Unlock mutex");
        }
    }
    return 0;
}

没看太理解申请为每个闹钟申请空间然后加到alarm_list 中是怎么加的。
请各位指教。