Cypress CSC-1200T Betriebsanweisung Seite 72

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72 Cray T3E User’s Guide
7.4.1 Using the SHMEM routines
SHMEM routines can be divided into a few basic categories according
to their respective tasks. The point-to-point communication routines
transfer data between two PEs, whereas collective routines involve data
transfer between several PEs. Reduction routines are used to find out
certain properties of data stored in the memories of a group of PEs.
Synchronization routines give the programmer a possibility to control
the order of calls to other SHMEM routines. Finally, there are some
cache management routines for taking care of data coherence.
7.4.2 Data addresses
Data objects are passed by address to SHMEM routines. This means that
the address of the remote data object must be known to the PE calling a
SHMEM routine. This is typically realized by having a corresponding data
object in the local memory. The data objects are then called symmetric.
The following data objects are symmetric on the T3E:
Fortran data objects in common blocks or with the SAVE attribute
Fortran arrays allocated with shpalloc
Fortran stack variables declared with a !dir$ symmetric direc-
tive.
non-stack C and C++ variables
C and C++ data allocated by shmalloc
C and C++ stack variables declared with a #pragma symmetric
directive
There is also another possibility besides having symmetric data objects
on different PEs, namely passing the address of a remote data object to
the calling PE before the actual call to a SHMEM routine is carried out.
In this case the remote data object is called asymmetric accessible.The
following data objects are asymmetric accessible on the T3E:
C and C++ data allocated by malloc and C++ data allocated by the
new operator
C and C++ variables with the automatic or register storage class
Fortran arrays allocated with hpalloc
Fortran PE-private data objects on the stack.
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