Pthread同步：两个文本文件的前后读取

Question

我在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，每行一个字符。

h 
0 
h 
0 
... 

第二的格式如下：：

第一像被格式化

0 
i 
0 
i 
0 
i 

有时可以有后彼此多个字母，或彼此先后多个零。但是，一个确定的是，如果一个文件的一行上有一个字母，第二个文件的相应行将有一个0，反之亦然。

线程应该保持读取文件输入到全局字符数组中，直到它们达到零。此时，他们允许另一个线程接管。他们会一直往前走，直到两个文件都被完全读取。 （1）很多h的变化，其次是许多i或（2）（正确答案）hihihi的连续流，或（3）有时很多我的其次是许多h。所以，我知道我的同步方法已关闭。

这是我的线程中的一个的示例： （注意两个线程是完全一样的，除了被打开的文件。）

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; 
} 

如果我能更好地使用锁定，解锁，等待和/或信号创建具有一致结果的工作同步技术，我将不胜感激。

Answer 1

下面是一个你想要的程序的尝试。虽然没有充分测试）;

#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; 
}