pthread_mutex_trylock

//pthread_mutex_trylock非阻塞时互斥锁

#include <iostream>
#include <pthread.h>
#include <ctime>
#include "errors.h"
#define sun
using namespace std;

pthread_mutex_t mutex=PTHREAD_MUTEX_INITIALIZER;
const int SPIN=100;
long counter;
time_t end_time;

void *pthread_counter_thread(void*)
{
    while(time(NULL)<end_time)
    {
        int status=pthread_mutex_lock(&mutex);
        if(status)
            err_abort(status,"Lock mutex");
        
        for(int spin=0;spin<SPIN;++spin)
            counter++;
        
        status=pthread_mutex_unlock(&mutex);
        if(status)
            err_abort(status,"Unlock mutex");
        
        sleep(1);
    }
    cout<<"Counter is :"<<counter<<endl;
    return NULL;
}

void *pthread_monitor_thread(void *)
{
    int status,misses=0;
    while(time(NULL)<end_time)
    {
        sleep(3);
        status=pthread_mutex_trylock(&mutex);
        if(status!=EBUSY)
        {
            if(status!=0)    
                err_abort(status,"Trylock mutex");
            
            cout<<"Pthread_mutex_trylock,Counter is :" <<counter/SPIN<<endl;
            
            status=pthread_mutex_unlock(&mutex);
            if(status!=0)
                err_abort(status,"Unlock mutex");
        }
        else
            misses++;
        
        cout<<"Moniter thread missed update :"<<misses<<"times."<<endl;
        return NULL;
    }
}

int main()
{    
    #ifdef sun
        cout<<"Setting concurrency level to 2"<<endl;
        pthread_setconcurrency(2);
    #endif
    
    pthread_t pthread_counter_id,pthread_monitor_id;
    end_time=time(NULL)+60;

    //创建 pthread_counter_thread
    int status=pthread_create(&pthread_counter_id,NULL,pthread_counter_thread,NULL);
    if(status)
        err_abort(status,"Create counter thread");

    //创建 pthread_monitor_thread
    status=pthread_create(&pthread_monitor_id,NULL,pthread_monitor_thread,NULL);
    if(status)
        err_abort(status,"Create monitor thread");

    //连接 pthread_counter_thread
    status=pthread_join(pthread_counter_id,NULL);
    if(status)
        err_abort(status,"Join counter thread");
    
    //连接 pthread_monitor_thread
    status=pthread_join(pthread_monitor_id,NULL);
    if(status)
        err_abort(status,"Join monitor thread");
    return 0;
}

1.
pthread_mutex_trylock函数间接性的报告计数器的值，仅当他对计数器的访问与计数线程没有冲突时才发生报告
counter_thread线程在更新计数器时保持互斥量的事件长短，增大该数值使monitor_thread线程中pthread_mutex_trylock函数
返回EBUSY值的概率增大
2.
计数线程每一秒醒来一次，锁住互斥量，计数器的数值增加，计数器，每秒增加SPIN
监控线程每三秒醒来一次，并试图加锁互斥量如果调用返回EBUSY，则监控线程计算失败的次数，然后再次等三秒，如果

pthread_mutex_trylock函数返回成功，则监控线程打印计数器counter当前的值
3.

pthread_setconcurrency(2);设置线程并发级别为2，允许监控线程和计数线程在单处理器中并发执行；
否则监控线程要等计数线程执行完之后才能执行