#20884: line buffering in sage-logger causes "hang" due to invisible prompt when
installing experimental packages
-------------------------------------+-------------------------------------
Reporter: mkoeppe | Owner:
Type: defect | Status: closed
Priority: critical | Milestone: sage-7.3
Component: build | Resolution: fixed
Keywords: | Merged in:
Authors: Erik Bray | Reviewers: Dima Pasechnik,
| Matthias Koeppe
Report Upstream: N/A | Work issues:
Branch: | Commit:
705573623266f1017aa4a433e816c0e878960836|
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Changes (by embray):
* commit: 705573623266f1017aa4a433e816c0e878960836 =>
Comment:
> How about simply changing the scripts to output a newline when prompting
the user for something, at least when the sage-logger is used?
Those scripts don't necessarily have any way to know that `sage-logger` is
being used, nor should they.
I think the test of just `cat`ting is not quite fair either. In a real
build the overhead of the commands being run far outweighs the overhead of
the logger. For example running `make patch` on current `develop` I got:
```
real 2m14.225s
user 0m29.614s
sys 1m2.397s
```
while on my branch:
```
real 2m18.844s
user 0m38.751s
sys 1m4.341s
```
So maybe possibly a little slower but hard to say from a single data
point.
There's no need to emphasize ''shell loop'' since it's using only shell
built-ins, or should be, so that shouldn't be a significant source of
overhead. Ultimately `sed` is looping over one character at a time too.
One thing that might speed this up a bit is to not `printf` for every
character, but at least buffer that.
Still, point partly taken. I might prefer to go with my earlier instinct
and just rewrite it in Python. I think using `sed` just to prepend to a
line also feels like a blunt instrument.
--
Ticket URL: <https://trac.sagemath.org/ticket/20884#comment:53>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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