NAME

       sc::MemoryGrp - The MemoryGrp abstract class provides a way of accessing distributed
       memory in a parallel machine.

SYNOPSIS

       #include <memory.h>

       Inherits sc::DescribedClass.

       Inherited by sc::MsgMemoryGrp, and sc::ProcMemoryGrp.

   Public Member Functions
       MemoryGrp (const Ref< KeyVal > &)
       int me () const
           Returns who I am.
       int n () const
           Returns how many nodes there are.
       virtual void set_localsize (size_t)=0
           Set the size of locally held memory.
       size_t localsize ()
           Returns the amount of memory residing locally on me().
       virtual void * localdata ()=0
           Returns a pointer to the local data.
       distsize_t localoffset ()
           Returns the global offset to this node's memory.
       int size (int node)
           Returns the amount of memory residing on node.
       distsize_t offset (int node)
           Returns the global offset to node's memory.
       distsize_t totalsize ()
           Returns the sum of all memory allocated on all nodes.
       virtual void activate ()
           Activate is called before the memory is to be used.
       virtual void deactivate ()
           Deactivate is called after the memory has been used.
       virtual void * obtain_writeonly (distsize_t offset, int size)=0
           This gives write access to the memory location. No locking is done.
       virtual void * obtain_readwrite (distsize_t offset, int size)=0
           Only one thread can have an unreleased obtain_readwrite at a time.
       virtual void * obtain_readonly (distsize_t offset, int size)=0
           This gives read access to the memory location. No locking is done.
       virtual void release_readonly (void *data, distsize_t offset, int size)=0
           This is called when read access is no longer needed.
       virtual void release_writeonly (void *data, distsize_t offset, int size)=0
           This is called when write access is no longer needed.
       virtual void release_readwrite (void *data, distsize_t offset, int size)=0
           This is called when read/write access is no longer needed.
       virtual void sum_reduction (double *data, distsize_t doffset, int dsize)
       virtual void sum_reduction_on_node (double *data, size_t doffset, int dsize, int node=-1)
       virtual void sync ()=0
           Synchronizes all the nodes.
       virtual void * malloc_local (size_t nbyte)
           Allocate data that will be accessed locally only.
       virtual double * malloc_local_double (size_t ndouble)
       virtual void free_local (void *data)
           Free data that was allocated with malloc_local_double.
       virtual void free_local_double (double *data)
       virtual void catchup ()
           Processes outstanding requests.
       virtual void print (std::ostream &o=ExEnv::out0()) const
           Prints out information about the object.

   Static Public Member Functions
       static MemoryGrp * initial_memorygrp (int &argc, char **argv)
           Create a memory group.
       static MemoryGrp * initial_memorygrp ()
       static void set_default_memorygrp (const Ref< MemoryGrp > &)
           The default memory group contains the primary memory group to be used by an
           application.
       static MemoryGrp * get_default_memorygrp ()
           Returns the default memory group.

   Protected Member Functions
       void obtain_local_lock (size_t start, size_t fence)
       void release_local_lock (size_t start, size_t fence)

   Protected Attributes
       int me_
       int n_
       distsize_t * offsets_
       int debug_

Detailed Description

       The MemoryGrp abstract class provides a way of accessing distributed memory in a parallel
       machine.

       Several specializations are available. For one processor, ProcMemoryGrp provides a simple
       stub implementation. Parallel specializations include ShmMemoryGrp, MTMPIMemoryGrp, and
       ARMCIMemoryGrp. The particular specializations that work depend highly on the target
       hardware and software environment.

Member Function Documentation

   virtual void sc::MemoryGrp::catchup () [virtual]
       Processes outstanding requests. Some memory group implementations don't have access to
       real shared memory or even active messages. Instead, requests are processed whenever
       certain memory group routines are called. This can cause large latencies and buffer
       overflows. If this is a problem, then the catchup member can be called to process all
       outstanding requests.

   static MemoryGrp* sc::MemoryGrp::get_default_memorygrp () [static]
       Returns the default memory group. If the default memory group has not yet been set, then
       one is created. The particular specialization used is determined by configuration options
       and which specializations are being used for MessageGrp and ThreadGrp.

   static MemoryGrp* sc::MemoryGrp::initial_memorygrp (int & argc, char ** argv) [static]
       Create a memory group. This routine looks for a -memorygrp argument, and then the
       environmental variable MEMORYGRP to decide which specialization of MemoryGrp would be
       appropriate. The argument to -memorygrp or the value of the environmental variable should
       be either string for a ParsedKeyVal constructor or a classname. The default ThreadGrp and
       MessageGrp objects should be initialized before this is called.

       References initial_memorygrp().

       Referenced by initial_memorygrp().

   virtual void* sc::MemoryGrp::malloc_local (size_t nbyte) [virtual]
       Allocate data that will be accessed locally only. Using this for data that will be used
       for global operation can improve efficiency. Data allocated in this way must be freed with
       free_local_double.

       Reimplemented in sc::ARMCIMemoryGrp.

   virtual void* sc::MemoryGrp::obtain_readwrite (distsize_t offset, int size) [pure virtual]
       Only one thread can have an unreleased obtain_readwrite at a time. The actual memory
       region locked can be larger than that requested. If the memory region is already locked
       this will block. For this reason, data should be held as read/write for as short a time as
       possible.

       Implemented in sc::ActiveMsgMemoryGrp, sc::ShmMemoryGrp, sc::RDMAMemoryGrp, and
       sc::ProcMemoryGrp.

   virtual void sc::MemoryGrp::release_readwrite (void * data, distsize_t offset, int size) [pure
       virtual]
       This is called when read/write access is no longer needed. The memory will be unlocked.

       Implemented in sc::ActiveMsgMemoryGrp, sc::ShmMemoryGrp, sc::RDMAMemoryGrp, and
       sc::ProcMemoryGrp.

   virtual void sc::MemoryGrp::set_localsize (size_t) [pure virtual]
       Set the size of locally held memory. When memory is accessed using a global offset
       counting starts at node 0 and proceeds up to node n() - 1.

       Implemented in sc::ActiveMsgMemoryGrp, sc::ShmMemoryGrp, sc::ARMCIMemoryGrp,
       sc::ProcMemoryGrp, sc::RDMAMemoryGrp, and sc::MsgMemoryGrp.

   virtual void sc::MemoryGrp::sync () [pure virtual]
       Synchronizes all the nodes. This is useful after remote memory writes to be certain that
       all of the writes have completed and the data can be accessed locally, for example.

       Implemented in sc::MTMPIMemoryGrp, sc::ARMCIMemoryGrp, sc::ProcMemoryGrp, and
       sc::MsgMemoryGrp.

Author

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