Pthread同步:返回&读两个文本文件

时间:2017-09-23 21:15:59

标签: c synchronization pthreads mutex semaphore

我正在编写一个创建两个线程的程序。每个线程负责读取一个文本文件,每行有一个字符。

第一种格式如下:

h
0
h
0
...

第二种格式如下:

0
i
0
i
0
i

有时可能会有多个字母在彼此之后,或者在彼此之后存在多个零。但是,可以肯定的是,如果一个文件的一行上有一个字母,则第二个文件的相应行将为0,反之亦然。

线程应该继续将文件输入读取到全局char数组中,直到它们达到零。此时,它们允许其他线程接管。他们一直来回走,直到两个文件完全被读取。

此时,当我跑步时,我得到的变化是:(1)很多h后面跟着很多我或(2)(正确答案)a连续的hihihi流,或(3)有时很多我跟着很多人。所以,我知道我的同步方法已关闭。

以下是我的一个主题的示例: (注意两个线程完全相同,但正在打开的文件除外。)

void *getMessage1()
{
FILE *studentOne = fopen("Student1", "r");

size_t howManyChars;
char *placeHolderChars; 
int count = 1;
while (count < 501)
{
    placeHolderChars = NULL;
    getline(&placeHolderChars, &howManyChars, studentOne);

    if(strcmp(placeHolderChars, "0\n") == 0) //if we've reached a zero
    {

         pthread_mutex_unlock(&lock); 
    }
    else
    {   while(1)
        {
            if(pthread_mutex_trylock(&lock) == 0)
            {

                break;
            }
        }

        if(strlen(placeHolderChars)>0)
        {
             placeHolderChars[1] = '\0';
        }

        strcat(message,placeHolderChars);
    }

    free(placeHolderChars);

    if(feof(studentOne))
    {

        pthread_mutex_unlock(&lock); //unlock
        fclose(studentOne);
        break;
    }
    count++;

 }

return 0;
}

这是我的主要方法:

int main(void)
{
pthread_t id1;
pthread_t id2;

pthread_create((&id1), NULL, getMessage1, NULL);
pthread_create((&id2), NULL, getMessage2, NULL);

pthread_join(id1, NULL);
pthread_join(id2, NULL);

int j;

for (j = 0; j < 1001; j++) 
{
     printf ("%c ",message[j]);
}

return 0;
}

对于如何更好地使用锁定,解锁,等待和/或信号来创建具有一致结果的工作同步技术,我将不胜感激。

1 个答案:

答案 0 :(得分:1)

这是一个尝试执行你想要的程序。但是,测试不充分;)

#include <iostream>
#include <fstream>
#include <string>

#include <cassert>
#include <pthread.h>



using std::cout;
using std::ifstream;
using std::string;

const string FILE1("file1.txt");
const string FILE2("file2.txt");

enum State
{
    UNINITIALIZED,
    THREAD_ONE_READS,
    THREAD_TWO_READS
};

struct ThreadInfo
{
    State state;
    string filename;
};

State state = UNINITIALIZED;
pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

void* thread_func(void* arg)
{
    // Open file 'h'.                                                                                                                                                                                                                                                                                                                                                                                                                  

    ThreadInfo ti = *reinterpret_cast<ThreadInfo*>(arg);
    ifstream infile;
    infile.open (ti.filename.c_str(), std::ifstream::in);

    // while (not EOF)                                                                                                                                                                                                                                                                                                                                                                                                                 
    //    Read 'h' or 'i': until 0 reached. Wake up other thread.                                                                                                                                                                                                                                                                                                                                                                      

    string line;
    getline(infile, line);
    while (infile.good())
    {
        cout << "Thread " << pthread_self() << " read " << line << '\n';
        pthread_mutex_lock(&mut);
        while (state == ti.state)
        {
            pthread_cond_wait(&cond, &mut);
        }
        pthread_mutex_unlock(&mut);

        assert(line.length() == 1);
        if (line[0] == '0')
        {
            pthread_mutex_lock(&mut);
            state = ti.state;
            cout << "Got 0, transferring, setting state to " << state << '\n';
            pthread_cond_signal(&cond);
            pthread_mutex_unlock(&mut);
        }
        else
        {
            cout << "Read char: " << line << '\n';
        }
        getline(infile, line);
    }

    pthread_mutex_lock(&mut);
    state = ti.state;
    cout << "Finishing thread, transferring, setting state to " << state << '\n';
    pthread_cond_signal(&cond);
    pthread_mutex_unlock(&mut);
}

int main()
{
    // Create thread 1                                                                                                                                                                                                                                                                                                                                                                                                                 
    // Create thread 2                                                                                                                                                                                                                                                                                                                                                                                                                 

    pthread_t thread_one_handle;
    pthread_t thread_two_handle;
    state = THREAD_ONE_READS;
    int result;

    ThreadInfo info1 = { THREAD_TWO_READS, FILE1 };
    result = pthread_create(&thread_one_handle, NULL, thread_func, &info1);
    assert(result == 0);

    ThreadInfo info2 = { THREAD_ONE_READS, FILE2 };
    result = pthread_create(&thread_two_handle, NULL, thread_func, &info2);
    assert(result == 0);

    result = pthread_join(thread_one_handle, NULL);
    assert(result == 0);
    result = pthread_join(thread_two_handle, NULL);
    assert(result == 0);
    cout << "main(): joined both worker threads, ending program.\n";

    return 0;
}