[PD-dev] Object crashes when trying to write to its outlet

[Christof Ressi]

I'm pretty sure it's because x_blksize is 0. (Internally, getbytes() 
always allocates at least 1 byte, which explains why you can 
successfully access the first sample.)

> In the new routine, I allocate memory likes this: 

In the new routine, you may only allocate the vectors that hold the 
input and output signals (t_sample **), as the number of channels won't 
change (well, unless you are creating a multi-channel object).

However, if you try to allocate buffers to cache the inputs, you can 
only do that in the "dsp" method, as this is the place where you know 
the actual blocksize.

I'm not really sure what you're trying to do. "x_in" and "x_out" are of 
type "t_sample **", so I would assume that they are supposed to hold the 
input/output signal vectors. However, then you allocate actual signal 
buffers for each channel which makes no sense to me. If you want to save 
the inputs, this would have to be *another* buffer. (Ideally, you would 
save all input signals in a single continuous buffer for better cache 
utilization.) There is (almost) never be a need to buffer the outputs*).

---

BTW, instead of posting code snippets, it would be more helpful to post 
(a link) to the whole source code, so we can get a better picture of 
what you're trying to do.

Christof

*) the only exception I can think of is when you use a library that uses 
a fixed floating point precision that does not match Pd's own precision. 
For example, I need to do this in my [vstplugin~] object, so it can use 
single-precision-only VST plugins in a double-precision Pd.

On 22.09.2023 12:32, Alexandros Drymonitis wrote:
> I'm trying to code an object with a variable number of inlets and 
> outlets, that's more complex than the one I posted a few days ago. 
> Writing to its input works fine, but when I try to write to its 
> output, Pd crashes. The culprit is when I try to access each 
> individual output.
>
> In the new routine, I allocate memory likes this:
>
> ```
> x->x_in = (t_sample **)getbytes(ninlets * sizeof(t_sample *));
> x->x_out = (t_sample **)getbytes(noutlets * sizeof(t_sample *));
> for (i = 0; i < ninlets; i++)
>     x->x_in[i] = (t_sample *)getbytes(x->x_blksize * sizeof(t_sample));
> for (i = 0; i < noutlets; i++)
>     x->x_out[i] = (t_sample *)getbytes(x->x_blksize * sizeof(t_sample));
> ```
>
> But Pd crashes when I try to access any output other that 
> x->x_out[0][0]. In a function that is called by the perform routine, I 
> do the following:
>
> ```
> for (i = 0; i < x->x_noutlets; i++) {
>     x->x_out[i][x->x_sample_index] = (t_sample)x->x_outvec[i];
> }
> ```
>
> and Pd crashes. Debugging with gdb pointed to this line. Changing the 
> code to x->x_out[0][0] does not crash Pd. I have also confirmed that 
> x->x_outvec[i] is not crashing Pd.
>
> Since memory for x->x_out has been allocated, and since I'm not trying 
> to access an element beyond this allocated memory (which is also 
> confirmed), why does Pd crash? Or am I doing something wrong in the 
> memory allocation part?
>
>
>
>
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