blocks|key|2518864|text|此程序使用MPI_Pack和MPI_Unpack在同一消息中发送两种不同类型的消息：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2518865|#include+<mpi.h>
#include+<stdio.h>

#define+ARRAY_SIZE(array)+\
++++(sizeof(array)+/+sizeof(array[0]))

struct+data_header+{
++++int32_t+x;
++++int32_t+y;
};

MPI_Datatype+dt_header;
MPI_Datatype+dt_vector;

void+sendmsg(void)+{
++++struct+data_header+header+=+{+1,+2+};
++++float+example[]+=+{+1.0,+2.0,+3.0,+4.0+};
++++char+buffer[4096];
++++int+position;

++++MPI_Pack(&header,+1,+dt_header,+buffer,+sizeof(buffer),+&position,+MPI_COMM_WORLD);
++++MPI_Pack(example,+1,+dt_vector,+buffer,+sizeof(buffer),+&position,+MPI_COMM_WORLD);
++++MPI_Send(buffer,+position,+MPI_PACKED,+0,+0,+MPI_COMM_WORLD);
}

void+recvmsg(void)+{
++++struct+data_header+header;
++++float+example[4];
++++char+buffer[4096];
++++int+position+=+0;

++++MPI_Recv(buffer,+sizeof(buffer),+MPI_PACKED,+1,+0,+MPI_COMM_WORLD,+MPI_STATUS_IGNORE);
++++MPI_Unpack(buffer,+sizeof(buffer),+&position,+&header,+1,+dt_header,+MPI_COMM_WORLD);
++++MPI_Unpack(buffer,+sizeof(buffer),+&position,+example,+1,+dt_vector,+MPI_COMM_WORLD);

++++printf("x+=+%25d,+y+=+%25d\n",+header.x,+header.y);
++++for+(int+index+=+0;+index+<+ARRAY_SIZE(example);+index%2B%2B)+{
++++++++printf("%25f+",+example[index]);
++++}
++++printf("\n");
}

int+main(void)+{
++++int+world_size;
++++int+world_rank;

++++MPI_Init(NULL,+NULL);
++++MPI_Comm_size(MPI_COMM_WORLD,+&world_size);
++++MPI_Comm_rank(MPI_COMM_WORLD,+&world_rank);

++++MPI_Type_contiguous(2,+MPI_INT,+&dt_header);
++++MPI_Type_commit(&dt_header);
++++MPI_Type_contiguous(4,+MPI_FLOAT,+&dt_vector);
++++MPI_Type_commit(&dt_vector);

++++if+(0+==+world_rank)+{
++++++++recvmsg();
++++}
++++else+{
++++++++sendmsg();
++++}

++++MPI_Finalize();

++++return+0;
}|code-block|syntax|javascript|2518866|输出|BOLD|2518867|x+=+1,+y+=+2
1.000000+2.000000+3.000000+4.000000+|2518868|这实际上只是一个概念验证代码。希望它能帮助你找到你正在寻找的解决方案。|2518869|便笺|2518870|此代码不进行错误检查，不应在生产环境中使用。|2518871|entityMap^0|5|8|E|A|0|0|0|2|0|0|0|0|2|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@$9|14|A|15|B|M]]|D|@]|E|$]]|$1|N|3|O|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|P|3|Q|5|6|7|17|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|18|8|@$9|19|A|1A|B|M]]|D|@]|E|$]]|$1|T|3|U|5|6|7|1B|8|@]|D|@]|E|$]]|$1|V|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|W|$]]

This program uses <code>MPI_Pack</code> and <code>MPI_Unpack</code> to send two different types in the same message:

<pre><code>#include &lt;mpi.h&gt;
#include &lt;stdio.h&gt;

#define ARRAY_SIZE(array) \
 (sizeof(array) / sizeof(array[0]))

struct data_header {
 int32_t x;
 int32_t y;
};

MPI_Datatype dt_header;
MPI_Datatype dt_vector;

void sendmsg(void) {
 struct data_header header = { 1, 2 };
 float example[] = { 1.0, 2.0, 3.0, 4.0 };
 char buffer[4096];
 int position;

 MPI_Pack(&amp;header, 1, dt_header, buffer, sizeof(buffer), &amp;position, MPI_COMM_WORLD);
 MPI_Pack(example, 1, dt_vector, buffer, sizeof(buffer), &amp;position, MPI_COMM_WORLD);
 MPI_Send(buffer, position, MPI_PACKED, 0, 0, MPI_COMM_WORLD);
}

void recvmsg(void) {
 struct data_header header;
 float example[4];
 char buffer[4096];
 int position = 0;

 MPI_Recv(buffer, sizeof(buffer), MPI_PACKED, 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
 MPI_Unpack(buffer, sizeof(buffer), &amp;position, &amp;header, 1, dt_header, MPI_COMM_WORLD);
 MPI_Unpack(buffer, sizeof(buffer), &amp;position, example, 1, dt_vector, MPI_COMM_WORLD);

 printf("x = %d, y = %d\n", header.x, header.y);
 for (int index = 0; index &lt; ARRAY_SIZE(example); index++) {
 printf("%f ", example[index]);
 }
 printf("\n");
}

int main(void) {
 int world_size;
 int world_rank;

 MPI_Init(NULL, NULL);
 MPI_Comm_size(MPI_COMM_WORLD, &amp;world_size);
 MPI_Comm_rank(MPI_COMM_WORLD, &amp;world_rank);

 MPI_Type_contiguous(2, MPI_INT, &amp;dt_header);
 MPI_Type_commit(&amp;dt_header);
 MPI_Type_contiguous(4, MPI_FLOAT, &amp;dt_vector);
 MPI_Type_commit(&amp;dt_vector);

 if (0 == world_rank) {
 recvmsg();
 }
 else {
 sendmsg();
 }

 MPI_Finalize();

 return 0;
}
</code></pre>

Output

<pre><code>x = 1, y = 2
1.000000 2.000000 3.000000 4.000000 
</code></pre>

This is really just proof-of-concept code. Hopefully, it will help you find the solution you are looking for.

Note

This code does no error checking and should not be used in a production environment.

I have n <code>workers</code>, 1 <code>master</code> (rank 0) and need to send messages via MPI from the n <code>workers</code> to the <code>master</code>. The message format is a variable length vector (<code>float *dta</code>) and constant size header <code>struct { int32_t x, int32_t y } dtaHdr</code>.

The master just loops through the incoming results and processes them. It is important for it to be able to associate which <code>dtaHdr</code>goes with which <code>dta</code>. 

I know how to:

<ol>
<li>Create <code>MPI_Datatype</code> for the constant sized <code>dtaHdr</code> and send it via P2P <code>MPI_Send</code>/<code>MPI_Recv</code>.</li>
<li>Send a variable length vector of any datatype (e.g. <code>MPI_Float</code>) via P2P <code>MPI_Send</code>/<code>MPI_Recv</code>.</li>
</ol>

The issue is I have no idea how to combine these two approaches. 

I know that I could:

<ul>
<li>Send header first and then the data second in two separate messages.

<ul>
<li>That has the problem of reordering &amp; interleaving of messages. I need a reliable, easy, and scalable way to associate the header and its data on <code>master</code>. With two messages I can't see a way how to always &amp; simply get both a header and data for incoming message on the master. I.e. two <code>worker</code>s could send hdr &amp; data messages to <code>master</code> &amp; they could become interleaved. (I'm not sure what the guarantees for ordering are TBH, even after reading MPI specification).</li>
</ul></li>
<li>Encode both the header and the data to a <code>MPI_Byte</code> array and send it esseentially as a binary blob. 

<ul>
<li>Sounds really dirty &amp; breaks some guarantees.</li>
</ul></li>
</ul>

My question is: how do I MPI-idiomatically send one identifiable logical message that contains both a constant sized header of one type and a variable sized vector of some second type.

Send variable length vector with constant header in one message

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有n个workers，1个master (秩0)，需要通过MPI从n个workers发送消息到master。消息格式是可变长度向量(float *dta)和恒定大小的报头struct { int32_t x, int32_t y } dtaHdr。主节点只是遍历传入的结果并对其进行处理。对于它来说，能够将哪个dtaH...

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