做网站如何安全 博客,如何提升网站的转化率,竞猜网站模板,国外建站用什么最多多线程读写同个文件会不会有访问冲突或者异常#xff1f;我们写个程序来测试一下
/*** Created by fangruibin* 测试多线程读写文件*/#include iostream
#include pthread.h
#include unistd.h
#include string.hconst char* fileName 我们写个程序来测试一下
/*** Created by fangruibin* 测试多线程读写文件*/#include iostream
#include pthread.h
#include unistd.h
#include string.hconst char* fileName test.txt;void processRead()
{FILE* fp fopen(fileName, r);if (fp NULL){printf(open file for read failed\n);return;}// 获取文件长度long startPos ftell(fp);fseek(fp, 0, SEEK_END);long endPos ftell(fp);long fileSize endPos - startPos;fseek(fp, 0, SEEK_SET);char* pBuf (char*)malloc(fileSize 1);size_t readSize fread(pBuf, 1, fileSize, fp);if ((long)readSize ! fileSize){printf(read not complete %ld\n, (long)readSize);}pBuf[fileSize] \0;if (strlen(pBuf) 0){printf(read empty\n);}printf(read:\n%s\n, pBuf);free(pBuf);fclose(fp);
}void processWrite()
{FILE* fp fopen(fileName, w);if (fp NULL){printf(open file for write failed\n);return;}const char* pData 2222222222222222222222222222\n2222222222222222222222222222\n2222222222222222222222222222\n;size_t dataLen strlen(pData);size_t writeLen fwrite(pData, 1, dataLen, fp);if (dataLen ! writeLen){printf(write not complete %ld\n, (long)writeLen);}fclose(fp);
}void processReadWrite(const char* pData)
{FILE* fp fopen(fileName, w);if (fp NULL){printf(open file for readwrite failed\n);return;}size_t dataLen strlen(pData);size_t writeLen fwrite(pData, 1, dataLen, fp);if (dataLen ! writeLen){printf(write not complete %ld\n, (long)writeLen);}// 获取文件长度fseek(fp, 0, SEEK_SET);long startPos ftell(fp);fseek(fp, 0, SEEK_END);long endPos ftell(fp);long fileSize endPos - startPos;fseek(fp, 0, SEEK_SET);char* pBuf (char*)malloc(fileSize 1);size_t readSize fread(pBuf, 1, fileSize, fp);if ((long)readSize ! fileSize){printf(read not complete %ld\n, (long)readSize);}pBuf[fileSize] \0;printf([rw] read:\n%s\n, pBuf);free(pBuf);fclose(fp);
}//线程1
void* threadFunc1(void* p)
{while (1){// const char* pData 111111111111111111111111111\n111111111111111111111111111\n;// processReadWrite(pData);processRead();usleep(100 * 1000);}return NULL;
}//线程2
void* threadFunc2(void* p)
{while (1){// const char* pData 222222222222222222222222222\n222222222222222222222222222\n;// processReadWrite(pData);processWrite();usleep(100 * 1000);}return NULL;
}int main()
{//初始化线程pthread_t hThread1;pthread_t hThread2;if (pthread_create(hThread1, NULL, threadFunc1, NULL) ! 0){printf(create thread 1 failed\n);return -1;}if (pthread_create(hThread2, NULL, threadFunc2, NULL) ! 0){printf(create thread 2 failed\n);return -1;}while (1){sleep(1);}return 0;
}
代码中我们设计了两个线程第一个线程从test.txt文件中读内容第二个线程不断地向test.txt文件写入内容然后我们看看读出来的内容和我们写入的内容是不是一样的
运行结果
fangfang-deepin:~/dev/chrifang/test/cpp/file$ ./multi_thread
read:
2222222222222222222222222222
2222222222222222222222222222
2222222222222222222222222222read not complete 0
read empty
read:read not complete 0
read empty
read:read not complete 0
read empty
read:read empty
read:read not complete 0
read empty
read:read not complete 0
read empty
read:read empty
read:read:
2222222222222222222222222222
2222222222222222222222222222
2222222222222222222222222222
可以看到有很多读取结果为空的证明多线程读写文件是会有访问冲突的。如何避免冲突呢
1) 同个进程内读写文件加上线程锁
2) 不同进程读写文件使用flock()函数去加锁
