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# sc::MemoryGrp Class Reference

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

`#include <memory.h>`

Inheritance diagram for sc::MemoryGrp:

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Collaboration diagram for sc::MemoryGrp:

[legend]
List of all members.

## Public Methods

| MemoryGrp ()
| MemoryGrp (const Ref< KeyVal > &)
virtual | ~MemoryGrp ()
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. More...
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. More...
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. More...
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. More...
virtual void * | malloc_local (size_t nbyte)
| Allocate data that will be accessed locally only. More...
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. More...
virtual void | print (std::ostream &o=ExEnv::out0()) const
| Prints out information about the object.

## Static Public Methods

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

## Protected Methods

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.

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.

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.

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.

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.

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.

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::ARMCIMemoryGrp.

The documentation for this class was generated from the following file:

- memory.h