On 09/26/2015 01:11 PM, Gilles wrote:
On Sat, 26 Sep 2015 09:53:30 +0200, Thomas Neidhart wrote:
On 09/26/2015 02:33 AM, Gilles wrote:
On Fri, 25 Sep 2015 16:52:26 -0700, Hasan Diwan wrote:
On 25 September 2015 at 16:47, Gilles
<gil...@harfang.homelinux.org>
wrote:
On Fri, 25 Sep 2015 17:30:33 +0200, Thomas Neidhart wrote:
On Fri, Sep 25, 2015 at 5:09 PM, Gilles
<gil...@harfang.homelinux.org>
wrote:
On Fri, 25 Sep 2015 07:28:48 -0700, Phil Steitz wrote:
On 9/25/15 7:03 AM, Gilles wrote:
On Fri, 25 Sep 2015 15:54:14 +0200, Thomas Neidhart
wrote:
Hi Ole,
for a start, I think you are asking the wrong
question.
First of all we need to agree that we want to add some
kind of
logging
facility to CM.
If the outcome is positive, there are a handful of
alternatives,
some of
them more viable than slf4j in the context of CM (e.g.
JUL or
commons-logging).
Could someone summarize why those alternatives were
deemed
"more
viable"?
btw. the same discussion has been done for other
commons
components as
well, and the result usually was: do not add logging
What was the rationale?
Look at the archives. We have discussed this multiple
times
in the
past in [math] and each time came to the conclusion that
Thomas
succinctly states above. What has changed now?
We also discussed several times to stick with Java 5.
Fortunately, that has changed. [Although sticking with
Java 7 is
still
a bad decision IMHO.]
As for logging, IIRC, the sole argument was "no
dependency"
because
(IIRC) of the potential "JAR hell".
that's not correct. The decision to not include any
dependencies has
nothing to do with "JAR hell".
Although I can't find it now, I'm pretty sure that I more
than once
got such an answer.
In order to prevent JAR hell, commons components strictly
stick
to the
"Versioning guidelines" [1]
I can't see how it relates.
But if you mean that no JAR hell can emerge from using a
logging
framework,
then that's good news.
The no-dependency rule is more related to the proposal of
the
component,
see [2]
Thanks for the reminder; in that document, we read:
(1) Scope of the Package
[...]
5. Limited dependencies. No external dependencies beyond
Commons
components and the JDK
So we are fine if use "Log4j 2" as kindly offered by Gary.
log4j is not a commons component btw.
Too bad for me. :-/
Case resolved, then, by the argument of authority?
I just pointed out that log4j is not a commons component and did
not
imply anything else.
"Commons" is OK but not another Apache project, by virtue of a
document that still refers to "JDK 1.2", "CVS", "Bugzilla" (not
to
mention that the "scope" of CM currently goes well beyond "the
most
common practical problems not immediately available in the Java
programming language")...
What's the _technical_ rationale for accepting this dependency
and
not accepting that dependency?
I have not seen a single example of a useful logging message
that
could
be added to commons-math, but we are already discussing which
framework
to use.
If it is not useful to you, why would you conclude that it is
not
useful to others?
At the cost of repeating myself, once more, the use-case is not
primarily about debugging CM, but sometimes one could need to
assess
how a "non-obvious" CM algorithm responds to an application's
request.
I've clearly expressed that use-case in a previous message.
Another example: I have a class that wraps a CM root solver; it
is
stuffed with log statements because the message contained in
the
"NoBracketingException" was utterly insufficient (and plainly
misleading due the default formatting of numbers) to figure out
why
certain calls succeeded and others not.
It's a problem (or a limitation) in the application, but in the
absence of other clues, tracing the solver could help figure
out a
workaround.
The alternative to the "logging" approach, would have been to
include
a precondition check before calling the solver, that would in
effect
duplicate the bracketing check done inside the solver. Given
the vast
amount of cases where the code ran smoothly, this is clearly a
sub-optimal solution as compared to turning logging on and
rerun the
case that led to a crash.
What can I say more about the usefulness (for a "low-tech"
person
like me) than the intro here:
http://logging.apache.org/log4j/2.x/manual/index.html
?
The examples with println debugging are not valid imho,
because how do
you know in advance what you will need to log in order to
successfully
debug some piece of code and such low-level information should
not be
captured in logs anyway.
Why are there several log levels? Low-level info can be routed
to
"DEBUG" or "TRACE".
As Ole put it quite eloquently, logging is a safety net that we
hope
we'll never need, until we do.
Each layer of an application has its own notion of what is the
appropriate log level. What is "INFO" for some low-level
library
will very probably not be so for most applications that use the
library.
Setting levels per package or class takes care of that: it's
the
library's *user* who chooses what is useful in the current
situation,
not the library's developer.
In the context of that asynchronous collaboration, the role of
the
library's developer is to carefully choose what *could* be
interesting, if the need should arise.
So, can we eventually discuss the _technical_ arguments against
logging inside CM, rather than personal opinion?
again, what I want to see is an example what *should* be logged
in the
case of an algorithm. Take the LevenbergMarquardtOptimizer as an
example:
* what did you log using System.out.println()?
* the algo computes a lot of internal data, which of these is
interesting for debugging problems or for general logging?
* there are various branches the algo can take, are just some
interesting to log, or all of them?
the use-cases presented so far were mainly about debugging
specific
problems, and I am *strongly* against adding logging information
just
for this purpose as you are clearly facing a dilemma here:
you have to log *everything* an algo does as otherwise you might
miss
the part that creates problems
but logging everything is not useful for a standard user of the
library
so it contradicts the original proposal to include logging
Again, CM is not an application where you need to log what it is
doing,
but a bunch of algorithms and utility methods to perform certain
calculations. I fail to see the need to add logging. What could
be
useful, and we had requests like that in the past, is to observe
the
state of a certain algorithm and to decide how to proceed in
certain
cases.
That is useful for users.
Another useful addition would be to add more aggressive
assertions. If
one user encounters a problem, he/she could run the application
with
assertions enabled and spot potential problems e.g. due to wrong
input.
Logging is a solution for a non existing problem imho.
Logging will not avoid the need to debug CM in case of problems
imho.
