互斥量-mutual exclusion  Posix API提供了互斥量的安全函数，

#include<pthread.h>

int phread_mutex_init(phread_mutex_t * tid,void * atrr);

int pthread_mutex_lock(pthread_mutex_t *tid);

int pthread_mutex_unlock(pthread_mutex_t * tid);

int pthread_mutex_trylock(pthread_mutex_t * tid);

                                  API  返回0为成功！一般返回一个正数的出错，在这里用—-char * strerror(int errno );

返回错误消息！

测试案例：

#include "unip.h"
/*
  mutual exclusing controls muti-alarming requestions;
*/
typedef struct alarm_tag{
   struct alarm_tag *link;
   int seconds;
   time_t times;
   char message[MAX];
}alarm_t;

alarm_t * alarm_list=NULL;
pthread_mutex_t alarm_mutex=PTHREAD_MUTEX_INITIALIZER;
void * alarm_thread(void *arg)
{
   alarm_t * alarm;
   int sleep_time;
   time_t now;
   int status;
   while(1)
   {
    status=pthread_mutex_lock(&alarm_mutex);
    if(status!=0)
    	Err_quit("mutex_lock error!");
    now=time(NULL);
    alarm=alarm_list;
    if(alarm==NULL)
    	sleep_time=1;
    else
    {
    	alarm_list=alarm_list->link;
    	if(alarm->times<=now)
    	{
    		sleep_time=0;
    	}
    	else
    		sleep_time=alarm->times-now;
    	printf("[waiting:%ld(%d)\"%s\"]\n",alarm->times,alarm->seconds,alarm->message);
    }
    status=pthread_mutex_unlock(&alarm_mutex);
    if(status!=0)
    	Err_quit("mutex_lock error!");
    if(sleep_time>0)
    {
    	sleep(sleep_time);
    }
    else
    	sched_yield();
    if(alarm!=NULL)
    {
    	printf("output:%d-----%s\n",alarm->seconds,alarm->message);
    	free(alarm);
    }
   }
}
int main(int argc, char const *argv[])
{
	time_t now;
	int seconds;
	int status;
	alarm_t *alarm,*next,**last,*head;
    char line[MAX];
    char message[MAX];
    memset(message,0,MAX);
    memset(line,0,MAX);
    pthread_t tid;
    status=pthread_create(&tid,NULL,alarm_thread,NULL);
    if(status!=0)
    {
         Err_quit("here pthread_create error!");
    }
    while(1){
    	printf("alarm>");
     if(fgets(line,sizeof(line),stdin)==NULL)
     	Err_quit("No Any data here");
     if(strlen(line)<=2)
     	continue;
     alarm=malloc(sizeof(alarm_t));
     if(alarm==NULL)
     	Err_quit("callocate error!\n");
     if(sscanf(line,"%d%64[^/n]",&seconds,message)<2)
     {
     	free(alarm);
     	break;
    }
    status=pthread_mutex_lock(&alarm_mutex);
    if(status!=0)
    	Err_quit("mutex_lock error!");
     memcpy(&alarm->message,message,MAX);
     alarm->seconds=seconds;
     alarm->times=time(NULL)+seconds;
     last=&alarm_list;
     next=*last;
     while(next!=NULL)
     {
     	if(next->times>=alarm->times)
     	{
     		alarm->link=next;
     		*last=alarm;
     		break;
     	}
     	last=&next->link;
     	next=next->link;
     }
     if(next==NULL)
     {
     	*last=alarm;
     	alarm->link=NULL;
     }

     for(head=alarm_list;head!=NULL;head=head->link)
     {
     	printf("%ld(%d)[\"%s\"]\n",head->times,head->seconds,head->message );
     }
     status=pthread_mutex_unlock(&alarm_mutex);
     if(status!=0)
    	Err_quit("mutex_lock error!");

 }
	return 0;
}

代码2:

#include "unip.h"
/*
  mutual exclusing controls muti-alarming requestions;
*/
#define SPIN 10000000
long couters;
/*
this program use trylock_function to tell counters in 
*/
time_t end_time;
pthread_mutex_t alarm_mutex=PTHREAD_MUTEX_INITIALIZER;

//header of list must be initialized here,it inited NULL (nothing);
void * threadfunc1(void *arg)
{
	int status;
	int spin;
    while(time(NULL)