infooverview.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

  \texttt{MPI_Info} provides a way to create a list of \texttt{(key,value)} pairs
  where the \texttt{key} and \texttt{value} are both strings.  Because many routines, both
  in the MPI implementation and in related APIs such as the BNR process
  management interface, require \texttt{MPI_Info} arguments, we define a simple 
  structure for each \texttt{MPI_Info} element.  Elements are allocated by the 
  generic object allocator; the head element is always empty (no \texttt{key}
  or \texttt{value} is defined on the head element).  
  
  The routines listed here assume that an info is just a linked list of 
  info items.  Another implementation would make \texttt{MPI_Info} an \texttt{MPID_List},
  and hang \texttt{MPID_Info} records off of the list.  For simplicity, we have 
  not abstracted the info data structures; routines that want to work
  with the linked list may do so directly.  Because the \texttt{MPI_Info} type is
  a handle and not a pointer, MPIU (utility) routines are provided to handle
  the allocation and deallocation of \texttt{MPID_Info} elements.

\subsection{Thread Safety}

  The info interface itself is not thread-robust.  In particular, the routines
  \texttt{MPI_INFO_GET_NKEYS} and \texttt{MPI_INFO_GET_NTHKEY} assume that no other 
  thread modifies the info key.  (If the info routines had the concept
  of a next value, they would not be thread safe.  As it stands, a user
  must be careful if several threads have access to the same info object.) 
  Further, \texttt{MPI_INFO_DUP}, while not 
  explicitly advising implementers to be careful of one thread modifying the
  \texttt{MPI_Info} structure while \texttt{MPI_INFO_DUP} is copying it, requires that the
  operation take place in a thread-safe manner.
  There isn\texttt{} much that we can do about these cases.  There are other cases
  that must be handled.  In particular, multiple threads are allowed to 
  update the same info value.  Thus, all of the update routines must be thread
  safe; the simple implementation used in the MPICH implementation uses locks.
  Note that the \texttt{MPI_Info_delete} call does not need a lock; the defintion of
  thread-safety means that any order of the calls functions correctly; since
  it invalid either to delete the same \texttt{MPI_Info} twice or to modify an
  \texttt{MPI_Info} that has been deleted, only one thread at a time can call 
  \texttt{MPI_Info_free} on any particular \texttt{MPI_Info} value.