mpid_segment_pack.tex

刚才是说明 现在是安装程序在 LINUX环境下进行编程的MPICH安装文件

\startmanpage
\mantitle{MPID{\tt \char`\_}Segment{\tt \char`\_}pack}{tex}{10/7/2002}
\manname{MPID{\tt \char`\_}Segment{\tt \char`\_}pack}
--- Pack up the designated buffer with a range of bytes. 
\subhead{Synopsis}
\startvb\begin{verbatim}
void *MPID_Segment_pack( MPID_Segment *segment, int *first, int *last, 
                       void *send_buffer ) 

\end{verbatim}
\endvb

\subhead{Input Parameters}
\startarg{segment }{Segment descriptor (initialized with {\tt MPID{\tt \char`\_}Segment{\tt \char`\_}init{\tt \char`\_}pack})
}
\startarg{send{\tt \char`\_}buffer }{Pointer to buffer to place data in.  May be {\tt NULL}, in which 
case {\tt MPID{\tt \char`\_}Segment{\tt \char`\_}pack} uses an internal buffer (and returns it).
}
\par
\subhead{Inout Parameters}
\startarg{first }{Pointer to first byte index to be packed (on input) or actually
packed (on output)
}
\startarg{last }{Pointer to last byte index to be packed (on input) or actually
packed (on output)
}
\par
\subhead{Return value}
Pointer to memory containing packed data.
\par
\subhead{Notes}
\par
Providing a send buffer allows implementations to make use of double
buffering without requiring that the segment code keep track of multiple
buffers.
\par
The values of {\tt first} and {\tt last} that are returned must satisfy the
following restrictions:
\startarg{1 }{(last-first) on output must be less than or equal to (last-first) on 
input.
}
\startarg{2 }{(last+1) on output must have the property that when used as first on a 
subsequent input, the value is unchanged.
}
\startarg{3 }{If first is zero on input, then first must be 0 on output.
}
\par
In addition, the {\em change} in first should be as small as possible.
For example, moving first so as to align the first byte on a word or
cache-line boundary (subject to the 3 requirements above) is allowed
(and is the reason to make first an in/out parameter).  However, as
rule three requires, if first is zero on input, no change to first is
allowed even for alignment purposes.  However, it is permissible to require
that the buffers satisfy language- or processor-specified alignment rules.
\par
\subhead{Module}
Segment
\par
\subhead{Questions}
If {\tt MPID{\tt \char`\_}Segment{\tt \char`\_}pack} returns an internal buffer, who is responsible for
freeing it?  It can't be a single static buffer because that isn't
thread-safe.  Is it freed as part of {\tt MPID{\tt \char`\_}Segment{\tt \char`\_}free}?
\par
If a send buffer is going to be provided, do we want to tell
{\tt MPID{\tt \char`\_}Segment{\tt \char`\_}init{\tt \char`\_}pack} so that no internal buffer is allocated?
\par
Should we return the number of bytes packed in a variable, just
to simplify the use of the result (which, after all, is a pointer {\em and
}a length)?
\endmanpage