680402 - Hang on certain site

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect)

Description

[Alice0775 White]

Attachment: WinDbg log

Build Identifier:
http://hg.mozilla.org/mozilla-central/rev/f69a10f23bf3
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:9.0a1) Gecko/20110818 Firefox/9.0a1 ID:20110818030747

Browser hang




Reproducible: Always

Steps to Reproduce:
1. Open Firefox with clean profile
2. Open Page ( http://www.openspc2.org/JavaScript/benchmark/addText2/index.html )
3. 


Actual Results:
  Browser hang

Expected Results:
  Display page in about 3sec on 2.5GHz C2Q

Regression window(cached m-c hourly),
Works:
http://hg.mozilla.org/mozilla-central/rev/b2aeaf724c8d
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b8pre) Gecko/20101208 Firefox/4.0b8pre ID:20101208215553
Hang:
http://hg.mozilla.org/mozilla-central/rev/0567fd4cf088
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b8pre) Gecko/20101208 Firefox/4.0b8pre ID:20101208230203
Pushlog:
http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=b2aeaf724c8d&tochange=0567fd4cf088

In local built(m-c repository)
built from 4861b72cc66d : hang
built from 0bd4cd152565 : fast

Triggered by:
4861b72cc66d	Jonathan Kew — bug 553981 - handle Hangul Jamo sequences and other special cases when marking clusters. r=karlt a=roc

Comment 1

[Alice0775 White]

Attachment: hang testcase.html

Comment 2

[Alice0775 White]

Attachment: not hang testcase.html

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: patch, v1 - avoid calling SanitizeGlyphRuns repeatedly during textrun construction with multiple scripts

The pathological behavior here arises when we try to construct a single textrun that has many separate script runs within it. The code ends up calling SanitizeGlyphRuns each time it appends a new glyph run, and that iterates over all the existing runs, which means we get behavior that is of the order of O(n^2) where n is the number of distinct glyph runs in the complete textrun, or something horrible like that. The testcase here is a worst-case scenario because it has mixed scripts repeated over and over within a single string for which we construct a giant textrun.

This patch should solve the problem by just calling SanitizeGlyphRuns once at the end of textrun construction, instead of repeating it for each added piece.

Comment 4

[Jonathan Kew [:jfkthame]]

Tryserver builds with this patch available at https://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/[e-mail]-df8cd5194cfd/.

Comment 5

[Alice0775 White]

The tryserver built is improved performance remarkably. (I expect early check-in!)

Comment 6

[Jonathan Kew [:jfkthame]]

jdaggett, review ping? This is a simple fix for a bad regression....

Comment 7

[John Daggett (:jtd)]

Comment on attachment 554556 [details] [diff] [review]
patch, v1 - avoid calling SanitizeGlyphRuns repeatedly during textrun construction with multiple scripts

Looks fine, but I think you should add a comment noting the details in comment 3 so that we remember what to avoid when restructuring code in the future.

Comment 8

[Jonathan Kew [:jfkthame]]

Pushed to inbound, with extra comments:
http://hg.mozilla.org/integration/mozilla-inbound/rev/153a1de6cd67

Comment 9

[Ed Morley [:emorley]]

http://hg.mozilla.org/mozilla-central/rev/153a1de6cd67