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<!-- $Id$ -->
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Author" CONTENT="James CE Johnson">
<TITLE>ACE Tutorial 021</TITLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
<CENTER><B><FONT SIZE=+2>ACE Tutorial 021</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Pooling your memories</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
Everything common the server & client is kept here. In
particular, the Constants class where we keep the names &
semaphore keys.
<p>
The Allocator class is just a thin wrapper around
ACE_Malloc<> that moves some of the details out of the
application logic.
<hr>
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#ifndef</font> <font color=purple>MPOOL_H</font>
<font color=blue>#define</font> <font color=purple>MPOOL_H</font>
<font color=red>// Everything else we need is in this one header</font>
<font color=blue>#include</font> "<A HREF="../../../ace/Malloc.h">ace/Malloc.h</A>"
<font color=blue>#if !defined</font> (<font color=purple>ACE_LACKS_SYSV_SHMEM</font>)
<font color=red>/*
With this we will abstract away some of the details of the memory
pool. Note that we don't treat this as a singleton because an
application may need more than one pool. Each would have a
different name and be used for different purposes.
*/</font>
class Allocator
{
public:
<font color=red>// The pool name will be used to create a unique semaphore to</font>
<font color=red>// keep this pool separate from others.</font>
Allocator (const char * _name = "<font color=green>MemoryPool</font>");
~Allocator (void);
typedef ACE_Malloc<ACE_MMAP_MEMORY_POOL, ACE_SV_Semaphore_Simple> pool_t;
<font color=red>// Provide an accessor to the pool. This will also allocate the</font>
<font color=red>// pool when first invoked.</font>
pool_t &pool (void);
protected:
<font color=red>// The name we gave to the pool</font>
char *name_;
pool_t *pool_;
};
<font color=red>/*
The client and server need to agree on a certain set of values. By
placing them in the Constants class we can eliminate a bit of confusion.
*/</font>
class Constants
{
public:
<font color=red>// The semaphore keys are needed for the two semaphores that</font>
<font color=red>// synch access to the shared memory area.</font>
static const int SEM_KEY_1;
static const int SEM_KEY_2;
<font color=red>// How big the pool will be and what we'll put into it. A real</font>
<font color=red>// app wouldn't need SHMDATA of course.</font>
static const int SHMSZ;
static const char *SHMDATA;
<font color=red>// The name assigned to the memory pool by the server is needed</font>
<font color=red>// by the client. Without it, the pool cannot be found.</font>
<font color=red>// Likewise, the name the server will bind() to the region of the</font>
<font color=red>// pool must be available to the client.</font>
static const char *PoolName;
static const char *RegionName;
};
<font color=blue>#endif</font> <font color=red>/* ACE_LACKS_SYSV_SHMEM */</font>
<font color=blue>#endif</font> <font color=red>/* MPOOL_H */</font>
</PRE>
<HR>
The really hard stuff is done by the ACE_Malloc<> template. This
template takes two parameters.<sup>*</sup> The first is a
memory pool class to use. ACE has several, I've choosen one
that uses a memory-mapped file. The second parameter is a lock
class of some sort. This is needed so that the ACE_Malloc<> can
protect its internal data. Note that you still have to
provide your own mutex around the data you put into the
malloc'd area.
<P>
* Actually, some implementations may require a different
number of parameters.
That's why ACE uses those funky macros. ACE_MMAP_MEMORY_POOL
for instance turns into ACE_MMAP_Memory_Pool on Linux but may
do other things on your platform.
<P><HR WIDTH="100%">
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