On Jan 25, 2015, at 1:26 PM, "Alan W. Irwin" <[email protected]> wrote:
> On 2015-01-24 22:34-0500 Jim Dishaw wrote:
>
>> Also, I would like to rewrite plAlloc2dGrid to use only one alloc
> because the multiple alloc algorithm that is currently used is
> unnecessary, slower, and on some OSes results in a fragmented heap. Also, by
> using one alloc call, plFree2dGrid needs only one free.
>
> I think not. I am pretty sure from code comments I have read in the
> past, the point of the two-dimensional mallocs (and frees) is to make
> dealing with dynamical two-dimensional arrays exactly the same as
> static two-dimensional arrays. That is a big benefit of the current
> code I would not want to give up.
>
The behavior of the two dimensional arrays would be exactly the same. Instead
of doing a malloc for the row pointers and then a series of mallocs for each
row, one malloc call is made for all the required space. I use this technique
all the time and here is some example code:
void one_allocate(float ***array, int m, int n)
{
void *mem;
float **ptr;
int i;
// Allocate one chunk of memory to store the array data
mem = malloc(
// Allocate for the row pointer
sizeof(float *) * m
// Allocate for the rows
+ sizeof(float) * m * n);
// Assign top of the memory chunk to
ptr = (float **)mem;
// Advance the memory pointer past the row pointer
mem = (void *)((float **)mem + m);
// Point each row pointer to a chunk of memory
// for storing one rows worth of data
for(i = 0; i < m; i++) {
ptr[i] = (float *)mem;
mem = (void *)((float *)mem + n);
}
(*array) = ptr;
}
I ran a benchmark and the one_allocate approach was almost 17 times faster (I
allocated and freed a 20 x 20 array).
>> [From a separate post] Does anyone build plplot with BUFFERED_FILE turned on
>
> I have looked through the entire source tree with the following
> command for mentions of BUFFERED_FILE.
>
> software@raven> find -type f |grep -v .git |xargs grep -l BUFFERED_FILE
> ./src/plcore.c
> ./src/plbuf.c
> ./include/plstrm.h
>
> And if you drop the -l option so you see all the instances, it is
> clear the BUFFERED_FILE macro is only used and not actually set.
> Actually there is substantial danger of a name clash here so
> "BUFFERED_FILE" could be set in some system header somewhere. So at
> minimum you should change this to PL_BUFFERED_FILE. However, I agree
> with your conclusion that this is just code clutter since it is
> definitely not set in our current CMake-based build system (in place
> for almost a decade now) and likely not set in our previous build
> system either. So I think (unless someone steps forward now to say
> this is experimental code they meant to get back to working on some
> day) you should go ahead and completely remove the code (from all 3
> files above) that would be compiled if BUFFERED_FILE was ever #defined
> or specified as a compiler option.
>
I added the BUFFERED_FILE ifdef blocks to turnoff the original temporary file
buffers when I implemented memory buffers. I did not want to delete the
original code in case the memory buffers was a horrible idea or if someone had
a low memory machine. I don't think anyone uses it because, as you pointed
out, it is not in the documentation.
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