[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [imaging] IMAGING-154 remove Debug class

Hello Bruno.

On Sun, 12 Aug 2018 08:56:37 +0000 (UTC), Bruno P. Kinoshita wrote:
Hi all,

I commented on IMAGING-154, but copying the last comment here as it
contains the approach I would like to follow to fix the last change in
the project blocking
a 1.0 release:


So went ahead to re-design the Debug class, in a way users could
still enable/disable debugging, and also use a PrintStream so that
other thing rather than System.out could be used.

Then, realized removing System.out was the natural next step. But
alas, the library uses System.out for debugging, but sometimes it uses
it for writing to System.out in a "verbose mode". What is more
complicated, is that sometimes classes methods like `toString()` are
calling debug methods that receive a PrintStream already.

So I spent some more time quickly comparing what other libraries I've
seen being used / or used for image processing:

Turns out only very low level libraries, such as the JNI bridge for
OpenCV, im4java, and Java's ImageIO can do with just throwing

All other libraries have one way or another of logging. Be it with
JUL, SLF4J, custom loggers, or with the ol' System.out/err.

My preferred compromise for this ticket was to keep Debug, making
System.out possible but optional, and mark the class internal only.
Now my preferred solution is to keep the Debug internal, but add a
logger to it. And then also add logging to replace where System.out is
used for the "verbose" mode.

Any thoughts? Objections? If none, I will try to work on this issue
next weekend, making the Debug class internal only, and replacing
System.out by a logging utility. After that, we should be good to
start preparing the vote for 1.0.

* I know it's hard to get a consensus on having logging in Commons
components, as we have  normally low level libraries, where using
logging is not always practical.

There are Log4j2 experts reading here.  It would be interesting
to hear them about what is practical or not.  There are several
aspects to "practical": simplicity, flexibility, compatibility,
performance, ...
How does Log4j2 fare in these areas?
Is there a known (through experience) limit in where it should
be used?

But I would now argue that Java own
ImageIO is low level. But ImageJ2, Processing, OpenJPEG, and Commons
Imaging are located at a higher level, some times even using it for
basic image handling/parsing/reading.

As with many discussions on this list, conflicting arguments occur
because people lack common (!) definitions.
So one goes: "You cannot do <something> in a low-level component"
but does not define "low-level"...

* Feel free to cast a counter-argument for it, but please think
whether you'd still be -0, +0 for this change. We have delayed 1.0 for
a while, so if you have a strong opinion on not adding a logger,
please provide an alternative for IMAGING-154.

Otherwise we may fail
to prepare a 1.0 release yet again, and then somebody else may have to
work on it in a few months/years...

We are there because the project is too rigid about itself as
a whole (cf. for example the [RNG] thread about BC).
IMHO, it's not the always least common denominator that is the
best decision...
As you noticed, components most easily stall in their development
for lack of proper review, or risk acceptance (i.e. assume that
those who are closer to the code (at a given time) probably know
best... :-/

My opinion is that we can take the risk to introduce logging, and
if people complain somehow, take it back later.

one possible compromise for this,
might be i) make Debug internal,


[Hmm... Does "internal" mean that minor release can break BC
on such a class?]

ii) remove all System.out calls,

+1 or

[Depends on what "low-level" means here. "stdout"/"stderr" is
indeed used in low-level utilities but is the intent the same

which means removing the verbose flags, the checks, and calls to
System.out in there.

It would be a loss of potentially useful information (e.g. for



From: Bruno P. Kinoshita <brunodepaulak@xxxxxxxxxxxx.INVALID>
To: Commons Developers List <dev@xxxxxxxxxxxxxxxxxx>
Sent: Tuesday, 6 February 2018 11:30 PM
Subject: Re: [imaging] IMAGING-154 remove Debug class

Hi sebb,

Another aspect of debugging is ensuring that methods are small and

easily tested independently.
However this is difficult to do, and care must be taken to ensure that
the public API is not unnecessarily extended..

A very good point.

The parsers in commons-imaging expose some #dump... methods


While I can see that parsers may need to dump the data they are
holding in some structured way for inspecting, reporting, serializing,
etc, it looks like some other classes were affected by it too. For

A JPEG Segment has a #dump() method


which gets defined in each subclass of Segment. It can be confusing
to have a method such as #dump() in a Segment, from the point of view
of someone writing a photo editor for example. The user could use that to pass his/her own logger's PrintWriter, which would make removing or
changing logging in the future in commons-imaging.

If we keep the Debug class, and make it internal, there would still
be these methods to take care. And there are some methods where users
can provide a PrintWriter, while others instead use System.out



From: sebb <sebbaz@xxxxxxxxx>
To: Commons Developers List <dev@xxxxxxxxxxxxxxxxxx>; Bruno P.
Kinoshita <brunodepaulak@xxxxxxxxxxxx>
Sent: Tuesday, 6 February 2018 11:06 PM
Subject: Re: [imaging] IMAGING-154 remove Debug class

On 6 February 2018 at 09:52, Bruno P. Kinoshita
<brunodepaulak@xxxxxxxxxxxx.invalid> wrote:
Hi Jorg,

I'd be fine with that solution too. I think this one would cause the smaller change to the code as is.

I believe my preference is still to remove the Debug class. But between logging and making Debug internal only, I'd choose making it internal.


I think making it internal means it can still be dropped later.

Looking forward to hearing what others think about these options.

Another aspect of debugging is ensuring that methods are small and
easily tested independently.
However this is difficult to do, and care must be taken to ensure that
the public API is not unnecessarily extended..


From: Jörg Schaible <joerg.schaible@xxxxxxxxxxxxxxx>
To: dev@xxxxxxxxxxxxxxxxxx
Sent: Tuesday, 6 February 2018 9:24 PM
Subject: Re: [imaging] IMAGING-154 remove Debug class

Hi Bruno,

if it might also be helpful to our users, why not keep and provide it. As

I understand it, the Debug class is a tool helping in development to

analyze some behavior.

Nothing stops us from declaring this class internal (we might even put it

into a package "internal" or "debug") that might be changed without

further comment. Nobody may rely on it in production code, but during

development it might be helpful. With such an approach we might not have

a need to find a better interface to provide this functionality.

Just my 2¢,


Am Mon, 05 Feb 2018 12:20:58 +0000 schrieb Bruno P. Kinoshita:


If memory serves me well, some time ago we had a discussion around

sanselan & commons-imaging 1.0. One of the issues with commons-imaging

1.0 was the Debug class.


I finished the pull request, but Gilles raised an important point, about

discussing other alternatives first.

Initially I am against logging in low level libraries, especially

commons components. But some time ago I had to debug TIFF issues in

commons-imaging, and having the dump methods was a tremendous help.

The issue is that some imaging algorithms/processing have a lot of

variables that can be altered. And keeping an eye on all of them in the

debugger can be quite hard - though not impossible.

So all in all, now I am more confident to proceed without the Debug

class. But some users could have a hard time investigating possible

issues in the library without seeing what's going on within the library.

IMO, that could be solved with the logging/dump features... or through a

better design, especially around exception handling/throwing. The latter

is my preferred approach. Instead of logging, I prefer - whenever

possible - that low level libraries throw exceptions and let me handle

the logging.

So, any thoughts? :) I'm +1 to remove the Debug class, and +0 to a

logging added to commons-imaging.


To unsubscribe, e-mail: dev-unsubscribe@xxxxxxxxxxxxxxxxxx
For additional commands, e-mail: dev-help@xxxxxxxxxxxxxxxxxx