First, to minimize ambiguity, it may make sense to distinguish
explicitly between two buffers: the send buffer (specified in the
MPI_Send or MPI_Bsend call) and the attached buffer (specified in some
MPI_Buffer_attach call).
Jovana Knezevic wrote:
On the other hand, a slight confusion when Buffered send is concerned remains:
In my understanding, MPI_SEND (standard, blocking) does not return
until the send operation it invoked has completed. Completion can mean
the message was copied into an MPI internal buffer, or it can mean the
sending and receiving processes synchronized on the message.
MPI_Send will return when it is safe to reuse the send buffer. No
guarantees about anything having to do with the receiver.
So, if we
decide to use buffered send (Bsend, so blocking), and we say "I want
to allocate a large enough buffer, I want my data to be copied into
the buffer then, because I do not want anyone else to decide if I am
going to syncronize completely my sends and receives on the message -
I know what I'm doing :-)!" then as soon as the data is copied to the
buffer, the call returns and the buffer can be reused.
MPI_Bsend will return when it is safe to reuse the send buffer. The
message data might simply have been copied to the local attached buffer.
Is the difference in comparison to Ibsend that with Ibsend the data
doesn't even have to be copied to the buffer when the call returns,
right.
or
something like that? Because otherwise, I still do not see the
difference: data copied into buffer-> call returns! Why wouldn't I
reuse my message-buffer then?!
