MPI学习(二)-非阻塞通信程序(无缓冲)

MPI-非阻塞通信程序(无缓冲)

非阻塞通信程序(无缓冲)是由MPI中的Isend和Ireceive来表示的，即异步通信。在这种情况下，发送进程发布一条“发送授权请求”(挂起的消息)的消息，并继续其程序的执行。当接收进程发布一个“同意发送”许可指令时，数据传输就启动了。所有的这些机制都是通过操作系统的信号进行内部管理的。当数据传输完成时，检查状态并指示进程是否可以安全地进行读/写数据。 需要注意的是原语MPI_Wait(&request,&status)等到数据传输完成(或中断后)，使用一个成为status的状态变量来指示数据传输是否已经成功。

相关的MPI原语

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int MPI_Isend(void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_comm comm, MPI_Request *req)
int MPI_Irecv(void *buf, int count, MPI_Datatype datatype, int src, int tag, MPI_Comm comm, MPI_Request *req)

MPI_Request结构中经常使用的：当*req操作完成时返回 *flag = 1,否则返回 0。

原语MPI_Wait一直等到*req所执行的操作完成。

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int MPI_Wait(MPI_Request *req, MPI_Status *status)

程序运行平台

北京超级云计算中心A3分区

环境变量

mpi/intel/2017.5

编译指令

mpicc mpi002.cpp -o mpi002

运行指令

mpirun -np 10 ./mpi002(本地提交,采取10个进程)

程序源代码

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#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include <math.h>
int main(int argc,char **argv)
{
	int myid, numprocs;
	int tag,source,destination,count;
	int buffer;
	MPI_Status status;
	MPI_Request request;
	MPI_Init(&argc,&argv);
	MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
	MPI_Comm_rank(MPI_COMM_WORLD,&myid);
	tag =2021; /* any integer to tag messages */
	source = 0;
	count = 1;
	if(myid != source )
	{
		buffer =2077;
		//其他进程向0号进程发送消息
		MPI_Isend(&buffer,count,MPI_INT,source,tag,MPI_COMM_WORLD,&request);
		MPI_Wait(&request,&status);
		printf("processor %d send %d to processor %d\n",myid,buffer,source);
	}

	if(myid == source )
	{
		//0号进程接收来自其他进程的消息
		for(int i=1;i<numprocs;i++)
		{
			MPI_Irecv(&buffer,count,MPI_INT,i,tag,MPI_COMM_WORLD,&request);
			MPI_Wait(&request,&status);
			printf("processor %d received %d from processor %d \n",myid,buffer,i);
		}
		
	}

	MPI_Finalize();
	return 0;
}

程序输出

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processor 2 send 2077 to processor 0
processor 3 send 2077 to processor 0
processor 5 send 2077 to processor 0
processor 6 send 2077 to processor 0
processor 7 send 2077 to processor 0
processor 8 send 2077 to processor 0
processor 9 send 2077 to processor 0
processor 4 send 2077 to processor 0
processor 1 send 2077 to processor 0
processor 0 received 2077 from processor 1 
processor 0 received 2077 from processor 2 
processor 0 received 2077 from processor 3 
processor 0 received 2077 from processor 4 
processor 0 received 2077 from processor 5 
processor 0 received 2077 from processor 6 
processor 0 received 2077 from processor 7 
processor 0 received 2077 from processor 8 
processor 0 received 2077 from processor 9