Review: std.logger

Mon Jul 21 15:53:25 PDT 2014

On Sunday, 20 July 2014 at 16:15:53 UTC, linkrope wrote:
> Pros
> ----
> The lighning talk about the std.logger proposal at DConf 2014 
> had a positive impact.
> We were able to change the "Current D Use" entry of our company 
> from
>     "Uses D2 / Phobos, Tango (log, xml)"
> to
>     "Uses D2 / Phobos, Tango (xml)".
> (We got rid of tango.util.log; we still rely on the fast 
> tango.text.xml.)

I didn't expect to hear from you about this, after you did not 
reply to my email about this topic.

If xml is problem for you, where is the PR?

>
> Cons
> ----
> 1. I am not happy with the (reverse) hungarian-style naming
>
> At least in the code of our company, logging a formatted string 
> is the basic use case.
> The function for the basic use case should not require a suffix 
> letter.
> The consistency argument, that 'infof' is like 'writef', does 
> not fully apply:
> neither 'infoln' nor 'infofln' make sense.
> (In my opinion, "half consistent" is inconsistent.)

so we have gone full circle now ....

>
> Currently, suffix 'c' is used for conditional logging.
> But, how will future extensions like glog's LOG_EVERY_N or 
> LOG_FIRST_N be named?

That's an easy one.

```
auto a = LOG_FIRST_N(1337);

logc(a, "Hello world");

auto b = WHAT_EVERY_THE(....);
logc(b, "Hello world again");
```

> With suffix 'e'? Suffix 'f' is already assigned!

what is 'e'?

> The suffix letter sequence seems to be the road to confusion.
>
> I would prefer the explicit naming of the previous std.log 
> proposal:
>     log.when(condition)(...)
> However, there is only a small advantage over
>     if (condition) log(...)

...

>
> 2. No support for 24/7 (server) applications
>
> In my opinion, I really need logging for applications that 
> possibly run forever.
> With the FileLogger, the file will grow forever.
> That's why most other frameworks provide something like a 
> RollingFileLogger or some "logrotate-aware" FileLogger.
>
> By the way: Instead of what I really need, I get a NullLogger.
> I have no clue, why I never ever missed such an oddity.

That was a user request, through github. Where I asked you to 
submit PRs and issues.

Have you tried subclassing Logger? I asked for PRs in the email I 
wrote to you at least twice.

>
> 3. Implementation is hidden behind 'mixin' expressions
>
> When I tried to look at the implementation, I found long 
> sequences of lines like this:
>     mixin(buildLogFunction(true, false, false, LogLevel.info));
>
> Nowadays, this changed into:
>     mixin(freeLog.format(
>         "info", "info", "info", "info",
>         "info", "info", "info", "info",
>         "info", "info", "info", "info",
>         "info", "info", "info", "info"));
>
> This is much better, but I still think, it's a complicated 
> solution for a simple problem.
> And it would be a shame for D, if there is no simple solution.

Yes please, suggestions?

>
> Small stuff
> -----------
> 4. FileLogger needs flush
>
> It's annoying when the events that caused a crash have been 
> logged, but they never have been written to the file.

I will fix that in the next session.

>
> 5. Suspect use of '__gshared'
>
> The FileLogger has a field
>     private __gshared File file_;
>
> In this case, "__gshared is equivalent to static".
> This means that all FileLogger instances share the same file!

I missed that, thank you

>
> 6. Bad naming of "StdIOLogger"
>
> Like 'std.stdio.StdioException', the 'io' should be lower case.
> If the 'StdIOLogger' logs to 'stdout', 'StdoutLogger' would be 
> preferable.

easy fix

>
> 7. No need for StdIOLogger
>
> 'stdout' (and 'stderr') are Files, so a FileLogger should be 
> able to handle them.
> A second constructor should do the trick.

It is a special file, I wanted to have that clear. two different 
classes does the trick for me.

>
> 8. Log levels
>
> Many frameworks mix the types "log level" and "set of log 
> levels" (for filtering).
> While 'trace', ..., 'fatal' are log levels, 'all' and 'off' 
> (better: 'none'?) are sets of log levels.
> (I have no idea about the type of 'unspecific'.)
>
> A clean separation would avoid confusion:
> why is there 'info(...)' but not 'all(...)'?

unspecific is about to be removed, all and off are pretty easy to 
understand but than ....

>
> Also, it would be easier to log for example 'trace' and 'info' 
> to 'stdout'.

not if you want to have that logged somewhere else.

>
> 9. Bad naming of "std.logger"
>
> The focus of this proposal is on the log/logging API; the 
> loggers are only examples.
>
> The recommended use should be
>     import log = std.logger;

you got that wrong, you can do it like that, nobody will force 
you and properly people will do it different.
You can also create a module wide global logger and use that

Again, std.logger is not the solution that works for every 
special case anybody comes up with out of the box. It is a set of 
ideas that enable you to have the logging tailored to your needs 
easily. On top of that, it allows you very fast access to basic 
logging that can be extend later on easily and seamlessly.

>
> Then, the name "std.log" (of the previous proposal) would be 
> more appropriate.
>
> Counter Proposal
> ----------------
> As a consequence of these issues, I once decided to spend a 
> weekend to prepare a counter proposal:
>
> http://code.dlang.org/packages/log
>
> The design goal was simplicity. So:
> - conditional logging is not supported
> - no suffix letter sequences

So you deleted code and functionality, hm?

> - there is no NullLogger

Same point

> - there is no MultiLogger (this functionality is implicit)

It is not, you can't remove Loggers individual and you can't 
build trees.

> - there is no need to provide a name for a logger

Because, you have no MultiLogger

>
> I prefer 'alias' over 'mixin':
> 'info' is just an alias for 'log(arg)' as well as for 'log(fmt, 
> args)' at log level 'info'.
>
> Sets of log levels are implemented as (bit) sets of log levels.
> A helper function lets you select the traditional >= filtering:
>     LogLevel.info.orHigher

So I need nine LogLevels, how do I add one between info and warn?

>
> For convenience, 'stdoutLogger' and 'stderrLogger' are factory 
> functions that create 'FileLogger' instances.

Object.factory

>
> Of course, a RollingFileLogger as well a a "RotatingFileLogger" 
> (that reopens the log file on SIGHUP) are provided.

Subclassing Logger should get the job done in under 30 lines.

>
> By now, this simple solution is in use in tens of thousands 
> lines of commercial code.
> (Where it outperforms the previously used tango.util.log 
> implementation.)

So what are the numbers for std.logger and where is the benchmark 
file to test it?

 From the source it looks like you kept parts of the design of 
std.logger and pulled out everything you didn't agree with. Also 
you only have global logging, to cite Brian: "Why?"

You added the parts, that you described are missing in 
std.logger. Of course your counter proposal will meet your needs 
then. I mean what would be the point of coding it up anyway else?