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I think that because your chunk size is constant, the memory manager
just returns previous blocks to you. So fragmentation does not
occur.<br>
<br>
On 24/09/2010 01:52, Ross Levis wrote:
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<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">Just wanted
some opinions on how bad a practice this is!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">I have written
a media player which uses a DLL to decode audio files.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">The DLL opens
an MP3 file for example, and sends back decoded raw audio,
usually in chunks of
4608 bytes (~20ms), but could be a different size.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">I need to
buffer this audio data for around 5 seconds (1 MB).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">Rather than
writing a complicated circular buffer which feeds in one end
and is taken from
the other, I decided to simply allocate memory for each new
chunk and store a
link from one memory location to the next. The oldest
buffer is read and
memory released.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">So there is roughly
1 new memory space being allocated and 1 being destroyed
every 20ms or so, with
around 200 chunks being stored at any one time.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">I’m using
D7 with the FastMM4 memory manager.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">It is working
very well with very little CPU usage at all, which I was
surprised at. I’ve
always been under the impression that allocating memory is a
slow process.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 12pt; color:
rgb(31, 73, 125);">Thoughts?<o:p></o:p></span></p>
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Regards<br>
<br>
<b>Rohit Gupta</b><br>
B.E. Elec., M.E., Mem IEEE, Member IET<br>
Technical Manager<br>
Computer Fanatics Ltd<br>
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