Bug 107577

Summary: Prevent race condition during Worker shutdown
Product: WebKit Reporter: Joshua Bell <jsbell>
Component: New BugsAssignee: Joshua Bell <jsbell>
Severity: Normal CC: benjamin, dimich, levin+threading, ojan.autocc, webkit.review.bot
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
Description Flags
Patch none

Description Joshua Bell 2013-01-22 12:06:31 PST
Prevent race condition during Worker shutdown
Comment 1 Joshua Bell 2013-01-22 12:14:46 PST
Created attachment 184031 [details]
Comment 2 Darin Adler 2013-01-22 14:31:38 PST
Comment on attachment 184031 [details]

View in context: https://bugs.webkit.org/attachment.cgi?id=184031&action=review

Patch looks fine, but there are a few stylistic issues worth fixing. review- to fix those

No need to have me be the one who reviews next time around.

> Source/WTF/ChangeLog:14
> +        (MessageQueue):
> +        (WTF):
> +        (WTF::::appendAndKill):

All three of these lines look bogus. Please fix them if the script generates something that looks like nonsense. Per-function comments are even better.

> Source/WebCore/ChangeLog:19
> +        (WorkerRunLoop):

Please remove this bogus line.

> Source/WebCore/workers/WorkerRunLoop.h:64
> +        void postTask(PassOwnPtr<ScriptExecutionContext::Task>, bool terminate = false);
> +        void postTaskForMode(PassOwnPtr<ScriptExecutionContext::Task>, const String& mode, bool terminate = false);

I’m not sure that a boolean or enum here is superior to a separate postTaskAndTerminate function. It seems that a separate function will work just fine:

    void postTaskAndTerminate(PassOwnPtr<ScriptExecutionContext::Task> task)
        m_messageQueue.appendAndKill(Task::create(task, defaultMode().isolatedCopy()));

No reason to touch these existing functions at all.

> Source/WebCore/workers/WorkerThread.cpp:275
> +        const bool terminate = true;
> +        m_runLoop.postTask(WorkerThreadShutdownStartTask::create(), terminate);

This named boolean argument idiom is not what we use for things like this in WebKit; it’s too easy for it to be wrong or get out of sync with the function we are calling. Instead we use enums, which is a perfect fit here. We can and should define an enum in WorkerRunLoop.h.
Comment 3 Joshua Bell 2013-01-22 14:46:17 PST
Thanks, darin@. Seemingly contradictory advice...

(In reply to comment #2)
> No reason to touch these existing functions at all.


> We can and should define an enum in WorkerRunLoop.h.

.. but I went with adding postTaskAndTerminate() since that seems the clearest.
Comment 4 Joshua Bell 2013-01-22 14:50:00 PST
Created attachment 184052 [details]
Comment 5 Joshua Bell 2013-01-22 15:35:46 PST
r+ anyone?
Comment 6 WebKit Review Bot 2013-01-22 15:47:14 PST
Comment on attachment 184052 [details]

Clearing flags on attachment: 184052

Committed r140483: <http://trac.webkit.org/changeset/140483>
Comment 7 WebKit Review Bot 2013-01-22 15:47:17 PST
All reviewed patches have been landed.  Closing bug.