关于pthread_mutex多个线程忙等待问题?

文档说如果对一个已加锁的mutex再次加锁pthread_mutex_lock会形成一个等待队列。可是这个示例有点奇怪,我知道线程没有放弃cpu,可是为什么后面输出的hello不到数量?

#ifndef THREAD_POOL_H
#define THREAD_POOL_H
#include <pthread.h>
#include <errno.h>
#include <iostream>
#include <unistd.h>
#include <queue>
class sample
{
public:
    void process();
};

template <typename T>
class threadPool
{
public:
    threadPool();
    void append(T &s);
    static void *worker(void *s);

private:
    std::queue<T *> tasks;
    pthread_t threads[5];
    bool run = true;
    pthread_mutex_t t;
};

// template <typename T>
// void threadPool<T>::append(T& s)
// {
//     pthread_t t;
//     pthread_create(&t,nullptr,worker,&s);
//     pthread_detach(t);
// }
template <typename T>
threadPool<T>::threadPool() : tasks()
{
    pthread_mutex_init(&t,nullptr);
    for(int i=0;i<5;++i)
    {
        pthread_create(&threads[i],nullptr,worker,this);
        pthread_detach(threads[i]);
    }
}

template <typename T>
void threadPool<T>::append(T &s)
{
    pthread_mutex_lock(&t);
    tasks.push(&s);
    printf("%d append.\n",pthread_self());
    pthread_mutex_unlock(&t);
}

template <typename T>
void *threadPool<T>::worker(void *s)
{
    auto pool=static_cast<threadPool<T>*>(s);
    while (pool->run)
    {
        pthread_mutex_lock(&(pool->t));
        if (pool->tasks.empty())
        {
            pthread_mutex_unlock(&(pool->t));
            printf("%d get the lock but continue.\n",pthread_self());
            continue;
        }
        auto work = pool->tasks.front();
        pool->tasks.pop();
        printf("%d get the lock and print\n",pthread_self());
        pthread_mutex_unlock(&(pool->t));
        work->process();
    }
    return nullptr;
}

#endif //!THREAD_POOL_H
#include "thread_pool.h"

void sample::process()
{
    std::cout<<"hello world.\n"<<std::endl;
}
#include "thread_pool.h"
#include <iostream>

int main(int argc, char **argv)
{
    threadPool<sample> pool;
    sample d[100];
    for(int i=0;i<100;++i)
    {
        pool.append(d[i]);
    }
    return 0;
}
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1268307712 get the lock but continue.
1285158720 append.
1268307712 get the lock and print
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1243129600 get the lock but continue.
1259915008 get the lock but continue.
1251522304 get the lock but continue.
hello world.
1285158720 append.

1268307712 get the lock and print
hello world.

1268307712 get the lock but continue.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1251522304 get the lock and print
hello world.

1251522304 get the lock and print
hello world.
1259915008 get the lock and print

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.
1285158720 append.
1251522304 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1285158720 append.
1234736896 get the lock and print
hello world.

1259915008 get the lock and print
hello world.

1259915008 get the lock and print
hello world.

1259915008 get the lock and print
hello world.
hello world.



1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1251522304 get the lock and print
hello world.

1251522304 get the lock and print
hello world.

1251522304 get the lock and print
hello world.

1251522304 get the lock and print
hello world.

1251522304 get the lock and print
hello world.

1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1251522304 get the lock but continue.
1268307712 get the lock but continue.
1259915008 get the lock but continue.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1234736896 get the lock and print
hello world.

1234736896 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock and print
hello world.

1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1243129600 get the lock but continue.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.
1285158720 append.

头晕了一下午,麻烦大佬出来解救众生。

Csdn user default icon
上传中...
上传图片
插入图片
抄袭、复制答案,以达到刷声望分或其他目的的行为,在CSDN问答是严格禁止的,一经发现立刻封号。是时候展现真正的技术了!