Race Condition

[ForbesLindesay]

I've found what I think is a race condition in less. Unfortunately the minimum example I can come up with involves 5 files. With the lessc command line it then outputs one of two different things at random. If you add the sync-imports flag, the problem is mitigated.

Inputs

index.less

@import "indirect-a.less";
@import "indirect-b.less";

body {
  color: @color;
}

indirect-a.less

@import "variables.less";
@import "override.less";

indirect-b.less

@import "variables.less";

variables.less

@color: red;

override.less

@color: black;

Command

lessc index.less

Output

One of the following two options is output at random:

Aprox 95% of the time:

body {
  color: #000000;
}

Aprox 5% of the time:

body {
  color: #ff0000;
}

This occurs with the latest version in npm and with the version currently in the GitHub repo.

[lukeapage]

cool many thanks for the repro case, I'll take a look

[lukeapage]

I've changed import-once to work out duplicates in a consistent way rather than relying on always taking the first file load that returns

[ForbesLindesay]

Thanks

[pmonegan]

Because I haven't tried it yet, the fixed outcome should be red?
On Feb 27, 2014 12:14 AM, "Luke Page" [email protected] wrote:

I've changed import-once to work out duplicates in a consistent way rather
than relying on always taking the first file load that returns

Reply to this email directly or view it on GitHubhttps://github.com//issues/1898#issuecomment-36213828
.

[seven-phases-max]

@pmonegan
Nope, it's actually black. The tricky part is that by default the @import directive implies once option, so the last occurrence of variables.less (set in indirect-b.less) is not expanded hence the latest definition is @color: black; (because the last imported file is override.less).

It will become red if you explicitly specify multiple flag for either indirect-b.less or for variables.less inside it, e.g.:

@import "indirect-a.less";
@import (multiple) "indirect-b.less";

body {
  color: @color;
}

[pmonegan]

Is this based only on node.js non - blocking, or as well in browser.
On Feb 28, 2014 12:22 PM, "Max Mikhailov" [email protected] wrote:

@pmonegan https://github.com/pmonegan
Nope, it's actually black. The tricky part is that by default the @importdirective implies
once http://lesscss.org/features/#import-options-once option, so the
last occurrence of "variables.less" (set in "indirect-b.less") is not
expanded hence the latest definition is @color: black; (because the last
imported file is "override.less").

Reply to this email directly or view it on GitHubhttps://github.com//issues/1898#issuecomment-36379075
.

[seven-phases-max]

I did not test in a browser, but it should be the same (and should not be affected by blocking/non-blocking stuff, unless there're some other hidden bugs of course).

[pmonegan]

Ok. I'll let you know if you haven't tested it by then.
On Feb 28, 2014 12:31 PM, "Max Mikhailov" [email protected] wrote:

I did not test in a browser, but it should be the same (and not depend on
blocking/non-blocking, unless there're some other hidden bugs).

Reply to this email directly or view it on GitHubhttps://github.com//issues/1898#issuecomment-36379973
.

[lukeapage]

It doesn't block loading files it just changes when it decides on the
duplicate.

[pmonegan]

Currently out of 100 browser refresh tests (FF, IE11) , @import is doing
what it's supposed to do. Same code returned @color: black each time.

On Fri, Feb 28, 2014 at 12:38 PM, Luke Page [email protected]:

It doesn't block loading files it just changes when it decides on the
duplicate.

Reply to this email directly or view it on GitHubhttps://github.com//issues/1898#issuecomment-36380649
.