doc: logging, clarify 'none level and the level ordering (#2407)

add the `'none` log level to the intro paragraph,
 declare `'none` the level of "least detail",
 and change prose to say "subscribes to current level and lower"

+2 small rewordings
This commit is contained in:
Ben Greenman 2018-12-04 16:03:38 -05:00 committed by GitHub
parent 8043768b4c
commit cbaa1b99d9
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23

View File

@ -9,19 +9,19 @@ A @deftech{logger} accepts events that contain information to be
logged for interested parties. A @deftech{log receiver} represents an
interested party that receives logged events asynchronously. Each
event has a topic and level of detail, and a @tech{log receiver} subscribes to
logging events at a certain level of detail (and higher) for a specific topic or for all topics. The
levels, in increasing order of detail, are @racket['fatal],
logging events at a certain level of detail (and lower) for a specific topic or for all topics. The
levels, in increasing order of detail, are @racket['none], @racket['fatal],
@racket['error], @racket['warning], @racket['info], and
@racket['debug].
To help organize logged events, a @tech{logger} can have a default topic and/or
a parent logger. Every event reported to a logger is also propagated to
its parent (if any), while the event message is prefixed with the logger's topic (if
a parent logger. Every event reported to a logger is propagated to
its parent (if any), and the event message is prefixed with the logger's topic (if
any) if the message doesn't already have a topic. Furthermore, events that are propagated
from a logger to its parent can be filtered by level and topic.
On start-up, Racket creates an initial logger that is used to
record events from the core run-time system. For example, an
record events from the core run-time system. For example, a
@racket['debug] event is reported for each garbage collection (see
@secref["gc-model"]). For this initial logger, two log receivers are
also created: one that writes events to the process's original error
@ -39,8 +39,9 @@ through environment variables:
The environment variable's value can be a @nonterm{level}:
@litchar{none}, @litchar{fatal}, @litchar{error},
@litchar{warning}, @litchar{info}, or @litchar{debug}; all
events the corresponding level of higher are printed. After an
@litchar{warning}, @litchar{info}, or @litchar{debug} (from low detail
to high detail); all
events at the corresponding level of detail or lower are printed. After an
initial @nonterm{level}, the value can contain
whitespace-separated specifications of the form
@nonterm{level}@litchar["@"]@nonterm{topic}, which prints