mpiu_object_add_ref.tex

来自「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」· TEX 代码 · 共 50 行

\startmanpage
\mantitle{MPIU{\tt \char`\_}Object{\tt \char`\_}add{\tt \char`\_}ref}{tex}{10/7/2002}
\manname{MPIU{\tt \char`\_}Object{\tt \char`\_}add{\tt \char`\_}ref}
--- Increment the reference count for an MPI object 
\subhead{Synopsis}
\startvb\begin{verbatim}
void MPIU_Object_add_ref( MPIU_Object_head *ptr )

\end{verbatim}
\endvb

\subhead{Input Parameter}
\startarg{ptr }{Pointer to the object.
}
\par
\subhead{Notes}
In an unthreaded implementation, this function will usually be implemented
as a single-statement macro.  In an {\tt MPI{\tt \char`\_}THREAD{\tt \char`\_}MULTIPLE} implementation,
this routine must implement an atomic increment operation, using, for
example, a lock on datatypes or special assembly code such as
\begin{verbatim}
   try-again:
      load-link          refcount-address to r2
      add                1 to r2
      store-conditional  r2 to refcount-address
      if failed branch to try-again:
\end{verbatim}

on RISC architectures or
\begin{verbatim}
   lock
   inc                   refcount-address or
\end{verbatim}

on IA32; "lock" is a special opcode prefix that forces atomicity.  This
is not a separate instruction; however, the GNU assembler expects opcode
prefixes on a separate line.
\par
\subhead{Module}
MPID{\tt \char`\_}CORE
\par
\subhead{Question}
This accesses the {\tt ref{\tt \char`\_}count} member of all MPID objects.  Currently,
that member is typed as {\tt volatile int}.  However, for a purely polling,
thread-funnelled application, the {\tt volatile} is unnecessary.  Should
MPID objects use a {\tt typedef} for the {\tt ref{\tt \char`\_}count} that can be defined
as {\tt volatile} only when needed?  For now, the answer is no; there isn't
enough to be gained in that case.
\endmanpage