Bug 31693

Summary: isMainThread() on Chromium (Mac and Linux) is so slow it timeouts LayoutTests..
Product: WebKit Reporter: Dmitry Titov <dimich>
Component: Web Template FrameworkAssignee: Nobody <webkit-unassigned>
Status: RESOLVED FIXED    
Severity: Normal CC: ap, dglazkov, levin
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: PC   
OS: OS X 10.5   
Attachments:
Description Flags
Proposed patch. levin: review+, dimich: commit-queue-

Description Dmitry Titov 2009-11-19 15:17:12 PST 
http://trac.webkit.org/changeset/51158 added ASSERT(isMainThread()) to TreeShared methods. This practically didn't slow down debug build on Mac and Windows, but on Chromium some layout tests started to timeout. For example, editing/selection/extend-selection.html execution time grew 15 times (!). This test operates with selection and it does a lot of operations like Position::previous() that churns refcout on Nodes.

Turned out the isMainThread() on pthread-based Chromium (Mac and Linux) involves mapping through threadMap, which in turn takes 2 Mutexes to lock - in identifierByPthreadHandle() and in iterator code.
By comparing handle itself rather then mapped Id the time required by isMainThread() goes back to reasonable.

Patch is coming.
Comment 1 Dmitry Titov 2009-11-19 15:21:03 PST 
Created attachment 43530 [details]
Proposed patch.
Comment 2 Alexey Proskuryakov 2009-11-19 15:26:36 PST 
Comment on attachment 43530 [details]
Proposed patch.

I wonder why you chose to rename the variable to mainThreadHandle. Mac man page for pthread_self says "returns the thread ID of the calling thread". Of course, "identifier" is taken already, but it's not a handle either.
Comment 3 Dmitry Titov 2009-11-19 15:33:56 PST 
Landed: http://trac.webkit.org/changeset/51211