(12)MPI-IO: fileview read_all_begin/end write_all_begin/end

最新推荐文章于 2018-09-25 08:26:30 发布

原创最新推荐文章于 2018-09-25 08:26:30 发布 · 707 阅读

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本文通过一个使用MPI库进行文件操作的例子，展示了如何为每个进程设置文件视图并进行非阻塞读写操作。该程序初始化MPI环境，打开一个文件，并为每个进程设置不同的偏移量来定义其文件视图。

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include"mpi.h"
/**
 * non-blocking read/write in the context of fileview in two stage
 * because *_end equals to MPI_Wait(&request, &status), MPI_Wait is not necessary
 * 	is equals to iread/iwrite with MPI_Wait
 *
 * int MPI_File_read_all_begin(MPI_File fh, void * buf, int count,  MPI_Datatype datatype)
 * int MPI_File_read_all_end(MPI_File fh, void * buf, MPI_Status * status)
 *
 * int MPI_File_write_all_begin(MPI_File fh, void * buf, int count, MPI_Datatype datatype)
 * int MPI_File_write_all_end(MPI_File fh, void * buf, MPI_Status * status)
 */
int main(int argc, char *argv[])
{
	int totalTaskNum, rankID;

	MPI_Init(&argc, &argv);
	MPI_Comm_rank(MPI_COMM_WORLD, &rankID);
	MPI_Comm_size(MPI_COMM_WORLD, &totalTaskNum);

	char *filename = "file.txt";
	MPI_File fh;
	MPI_Status status;
	MPI_File_open(MPI_COMM_WORLD, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);

	MPI_Offset offset = rankID * 128;
	//each process will has its file view which starts with offset
	MPI_File_set_view(fh, offset, MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL);

	MPI_Offset seek_offset = 0;
	int whence = MPI_SEEK_SET;
	//after set fileview, the seek is the context of new fileview
	MPI_File_seek(fh, seek_offset, whence);

	//write start with seek's position
	char write_buf[128];
	sprintf(write_buf, "rankID = %d, totalTaskNum = %d\n", rankID, totalTaskNum);
	MPI_File_write_all_begin(fh, write_buf, strlen(write_buf), MPI_CHAR);
	MPI_File_write_all_end(fh, write_buf, &status);

	//after write, the position has been moved, so let's go back via seek
	MPI_Offset seek_offset2 = 0;
	int whence2 = MPI_SEEK_SET;
	//after set fileview, the seek is the context of new fileview
	MPI_File_seek(fh, seek_offset2, whence2);

	//read start with seek's position
	char read_buf[128];
	MPI_File_read_all_begin(fh, read_buf, sizeof(read_buf), MPI_CHAR);
	MPI_File_read_all_end(fh, read_buf, &status);
	printf("rankID = %d, content = \'%s\'\n", rankID, read_buf);

	MPI_File_close(&fh);//after open, fh has the communicator info

	MPI_Finalize();
	return 0;
}