運行程序時出現分段錯誤並改變輸出

Question

我有一個程序應該將文件的內容完全複製到使用多個線程的另一個文件中。閱讀器線程從文件中讀取一行並將其存儲在循環緩衝區中。寫入器線程然後從緩衝區讀取並寫入文件。但是，我收到了分段錯誤，並且沒有寫入文件。任何想法爲什麼我得到一個分段錯誤，或者有什麼辦法，我可以找出是什麼導致了錯誤？

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <pthread.h> 
#include <semaphore.h> 

FILE *inputFile; 
FILE *outputFile; 

pthread_mutex_t mutex; 

int endOfFile = 0; 

typedef struct bufferStruct{ 
    int capacity; 
    int size; 
    int head; 
    int tail; 
    char **data; 
}buffer; 

buffer * bufferInit(int maxElements){ 
    buffer *buf; 
    buf = (buffer *)malloc(sizeof(buffer)); 

    buf->data = (char**)malloc(sizeof(char*)*maxElements); 
    buf->size = 0; 
    buf->capacity = maxElements; 
    buf->head = 0; 
    buf->tail = -1; 

    return buf; 
} 

void popFront(buffer *buf){ 
    if(buf->size != 0){ 
     free(buf->data); 
     buf->size--; 
     buf->head++; 
     if(buf->head == buf->capacity){ 
      buf->head = 0; 
     } 
    } 
    return; 
} 

char* front(buffer *buf){ 
    if(buf->size != 0){ 
     return buf->data[buf->head]; 
    } 

    return NULL; 
} 

void pushBack(buffer *buf, char *data){ 
    if(buf->size == buf->capacity){ 
     printf("Queue is Full\n"); 
    } 

    else{ 
     buf->size++; 
     buf->tail = buf->tail + 1; 

     if(buf->tail == buf->capacity){ 
      buf->tail = 0; 
     } 

     buf->data[buf->tail] = (char *) malloc((sizeof data + 1)* sizeof(char)); 

     strcpy(buf->data[buf->tail], data); 
    } 
    return; 
} 

buffer *buf; 

void* reader(void* arg){ 
    char line[1024]; 
    while(endOfFile != 1){ 
     fgets(line, sizeof(line), inputFile); 
     printf("Line read: %s", line); 

     pushBack(buf, line); 

     if(feof(inputFile)){ 
      endOfFile = 1; 
     } 
    } 
    pthread_exit(0); 
} 

void* writer(void* arg){ 
    char *line; 
    while(endOfFile != 1){ 
     pthread_mutex_lock(&mutex); 
     line = front(buf); 
     fputs(line, outputFile); 
     popFront(buf); 
     pthread_mutex_unlock(&mutex); 
    } 
    pthread_exit(0); 
} 

int main(int argc, char **argv){ 
    if (argc < 4) { 
     printf("Usage: %s <input file> <output file> <number>\n", argv[0]); 
     exit(-1); 
    } 

    inputFile = fopen(argv[1], "r"); 
    outputFile = fopen(argv[2], "w"); 
    int numOfThreads = atoi(argv[3]); 

    buf = bufferInit(16); 

    pthread_t readerTids[numOfThreads]; 
    pthread_t writerTids[numOfThreads]; 

    pthread_mutex_init(&mutex, NULL); 

    for(int i = 0; i < numOfThreads; i++){ 
     if(endOfFile != 1){ 
      pthread_attr_t attr; 
      pthread_attr_init(&attr); 
      pthread_create(&readerTids[i], &attr, reader, NULL); 
      pthread_create(&writerTids[i], &attr, writer, NULL); 

      printf("Thread %d created\n", i); 
     } 
    } 

    for (int i = 0; i < numOfThreads; i++) { 
     pthread_join(readerTids[i], NULL); 
     pthread_join(writerTids[i], NULL); 
    } 

    fclose(inputFile); 
    fclose(outputFile); 
} 

Answer 1

考慮到讀者線程比寫入者線程慢的可能性。作家線程獨自擁有鎖定，鎖定和解鎖，而不是困擾讀者。當閱讀器尚未更新緩衝區時，如果作者試圖使用緩衝區，該怎麼辦？使用線程同步，例如信號量，它沒有任何所有權問題。

void* reader(void* arg){ 
    char line[1024]; 
    while(endOfFile != 1){ 
     fgets(line, sizeof(line), inputFile); 
     printf("Line read: %s", line); 

     pushBack(buf, line); 

--- Lock semaphore here--- 

     if(feof(inputFile)){ 
      endOfFile = 1; 
     } 
    } 
    pthread_exit(0); 
} 


void* writer(void* arg){ 
    char *line; 
    while(endOfFile != 1){ 

-- Unlock semaphore here--- 

     line = front(buf); 
     fputs(line, outputFile); 
     popFront(buf); 
    } 
    pthread_exit(0); 
} 

與互斥鎖不同，兩個線程之間可以使用相同的信號量。這可以幫助你同步兩個線程。