On Sat, 26 Sep 2015 10:02:12 -0700, Phil Steitz wrote:
On 9/26/15 9:42 AM, Gilles wrote:
On Sat, 26 Sep 2015 09:03:06 -0700, Phil Steitz wrote:
On 9/26/15 4:56 AM, Thomas Neidhart wrote:
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.
+1
The other thing I would add is that the one place where it does
make
sense to dump text is in exception error messages, which is a place
where I think we could really improve things. Fortunately, that is
fairly easily done.
I have seen nothing in this thread to convince me that adding
logging in [math] will be net positive for either those of us who
maintain the component or for users. If we are not providing clear
exception error messages and/or APIs (with complete documentation)
so that users can understand what they need to debug their
applications, then we should focus on solving those problems.
Phil
First, you carefully do not reply to any of the concrete arguments
given in this thread, second you give a conclusion to an issue not
reported in this thread: exceptions and logging do not provide the
same service.
I am sorry, Gilles, but amidst all of the verbiage, I have not seen
any concrete arguments showing any specific and compelling use case
There were at least 3 specific examples of real cases (a bug in CM,
a way to help debug an application using CM, a tool to help refactor
an overly convoluted code in CM).
Then Ole also gave quite a few others in a very constructive post
that took the time to reply point-by-point to your objections.
Faced with some reluctance (which is by itself acceptable), we try to
make our points more specific by expanding that which we otherwise
think is obvious; but that is called "verbiage".
I have not seen any technical argument against logging.
See below for non-technical opinions that are at 180 degrees of
your views on the subject.
If you could accept that in this area also, it may be possible
that no hard rules are needed.
showing the need for logging. Somewhere above there is a reference
to not being able to figure things out based on exception messages,
so I mentioned that improving them could help.
That was part of the second example, saying that even the most
excruciatingly precise error message would not have helped.
Context is what mattered more.
At least, I'd wish that people sharing their own opinion (it's
nothing more since _zero_ technical argument against logging have
been put forth) stop taking the collective "users" on their side.
As for *actual* users/maintainers, Ole and I have a need, while
Thomas and you haven't. Those are all the facts that exist until
now.
I guess I am dense, but I still don't understand the need. Can you
try to give a specific use case that says more than "I don't want to
run a debugger and I need to see what the variables are?"
This is actually one of the points! Aren't we in good company
with this quote (found at our fellow Apache Log4J people's site):
-----
As Brian W. Kernighan and Rob Pike put it in their truly excellent book
"The Practice of Programming":
As personal choice, we tend not to use debuggers beyond getting a stack
trace or the value of a variable or two. One reason is that it is easy
to get lost in details of complicated data structures and control flow;
we find stepping through a program less productive than thinking harder
and adding output statements and self-checking code at critical places.
Clicking over statements takes longer than scanning the output of
judiciously-placed displays. It takes less time to decide where to put
print statements than to single-step to the critical section of code,
even assuming we know where that is. More important, debugging
statements stay with the program; debugging sessions are transient.
-----
The following is also a nice reading for another opinion on logging:
http://vasir.net/blog/development/how-logging-made-me-a-better-developer
And... I don't want to run a debugger. :-!
Gilles
Phil
In such a situation, what do we do as a project; maintain the status
quo, or try for a change?
On numerous occasions over the years, the status quo was enforced;
and I don't see that it benefited the project in terms of new
contributors.
So I'm +1 for trying to change, for a change.
Gilles
Thomas
My long-standing mentioning of slf4j was only because of its
"weightlessness" (thanks to the no-op implementation of its
API).
If "Log4j 2" has followed this path, good for everyone.
No objection, then?
I'm still not clear what log4j 2 adds -- most Apache java
projects
seem to
use log4j 1.2, seems to work well. -- H
I can only answer about "slf4j" where the "f" stands for
facade: it's
"only"
an API, with bridges to several logging frameworks (log4j,
logback,
etc.).
The separation of concerns (API vs one of several
implementations to
choose from)
allows the top-level application to uniformly configure
logging or to
disable it
completely (if choosing the "no-op" implementation).
That is virtually true for all logging frameworks, including
log4j,
slf4j, commons-logging.
Has it always been true?
I'm certainly no expert; I only try to stay clear of tools
about which
people complain a lot. A few years ago, that was the case of
jcl and
jul as compared to slf4j.
Gilles
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