MPI_Ssend/MPI_Issend 是否使用系统缓冲区？
Does MPI_Ssend/MPI_Issend use a system buffer?
根据文档，MPI_Ssend 和 MPI_Issend 是阻塞和非阻塞发送操作，两者都是同步的。 MPI 规范说，当接收方开始接收消息时，同步 发送完成，之后可以安全地更新发送缓冲区：
The functions MPI_WAIT and MPI_TEST are used to complete a nonblocking
communication. The completion of a send operation indicates that the
sender is now free to update the locations in the send buffer (the
send operation itself leaves the content of the send buffer
unchanged). It does not indicate that the message has been received,
rather, it may have been buffered by the communication subsystem.
However, if a synchronous mode send was used, the completion of the
send operation indicates that a matching receive was initiated, and
that the message will eventually be received by this matching receive.
请记住，同步发送在刚开始接收时被认为已完成，我不确定以下内容：
- 有可能是在
MPI_Ssend或MPI_Issend发出发送完成信号的那一刻，只从发送缓冲区中读取了一部分数据？例如，前N个字节已发送和接收，而后M个字节仍在发送中。
- 在收到整个消息之前，调用者如何才能安全地修改数据？这是否意味着数据必须被复制到系统缓冲区？据我了解，MPI 标准允许使用系统缓冲区但并不要求它。此外，从 here 我读到
MPI_Issend() 不会 在本地缓冲数据。
MPI_Ssend()（或与 MPI_Issend() 相关的 MPI_Wait()）returns 当 :
- 接收方已开始接收消息
- 和发送缓冲区可以重复使用
如果消息被完全接收，或者 MPI 库在本地缓冲数据，则满足第二个条件。
我没有读到 MPI 标准禁止数据缓冲。
来自标准，MPI 3.1 chpt 3.4 第 37 页
A send that uses the synchronous mode can be started whether or not a matching
receive was posted. However, the send will complete successfully only if a matching receive is
posted, and the receive operation has started to receive the message sent by the synchronous
send. Thus, the completion of a synchronous send not only indicates that the send buffer
can be reused, but it also indicates that the receiver has reached a certain point in its
execution, namely that it has started executing the matching receive. If both sends and
receives are blocking operations then the use of the synchronous mode provides synchronous
communication semantics: a communication does not complete at either end before both
processes rendezvous at the communication. A send executed in this mode is non-local.
根据文档，MPI_Ssend 和 MPI_Issend 是阻塞和非阻塞发送操作，两者都是同步的。 MPI 规范说，当接收方开始接收消息时，同步 发送完成，之后可以安全地更新发送缓冲区：
The functions MPI_WAIT and MPI_TEST are used to complete a nonblocking communication. The completion of a send operation indicates that the sender is now free to update the locations in the send buffer (the send operation itself leaves the content of the send buffer unchanged). It does not indicate that the message has been received, rather, it may have been buffered by the communication subsystem. However, if a synchronous mode send was used, the completion of the send operation indicates that a matching receive was initiated, and that the message will eventually be received by this matching receive.
请记住，同步发送在刚开始接收时被认为已完成，我不确定以下内容：
- 有可能是在
MPI_Ssend或MPI_Issend发出发送完成信号的那一刻，只从发送缓冲区中读取了一部分数据？例如，前N个字节已发送和接收，而后M个字节仍在发送中。 - 在收到整个消息之前，调用者如何才能安全地修改数据？这是否意味着数据必须被复制到系统缓冲区？据我了解，MPI 标准允许使用系统缓冲区但并不要求它。此外，从 here 我读到
MPI_Issend()不会 在本地缓冲数据。
MPI_Ssend()（或与 MPI_Issend() 相关的 MPI_Wait()）returns 当 :
- 接收方已开始接收消息
- 和发送缓冲区可以重复使用
如果消息被完全接收，或者 MPI 库在本地缓冲数据，则满足第二个条件。
我没有读到 MPI 标准禁止数据缓冲。
来自标准，MPI 3.1 chpt 3.4 第 37 页
A send that uses the synchronous mode can be started whether or not a matching receive was posted. However, the send will complete successfully only if a matching receive is posted, and the receive operation has started to receive the message sent by the synchronous send. Thus, the completion of a synchronous send not only indicates that the send buffer can be reused, but it also indicates that the receiver has reached a certain point in its execution, namely that it has started executing the matching receive. If both sends and receives are blocking operations then the use of the synchronous mode provides synchronous communication semantics: a communication does not complete at either end before both processes rendezvous at the communication. A send executed in this mode is non-local.