Should getWorkLoop be thread-safe?

• Subject: Should getWorkLoop be thread-safe?
• From: Howard Gayle <email@hidden>
• Date: Thu, 03 Aug 2006 10:10:36 -0400
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Apple's "I/O Kit Fundamentals" guide
http://developer.apple.com/documentation/DeviceDrivers/Conceptual/IOKitFundamentals/index.html
has an example under
   Handling Events > Work Loops > Listing 7-1
of overriding getWorkLoop().  The example tries to make
getWorkLoop() thread-safe.  I have some concerns about the
example code, but does getWorkLoop() really need to be
thread-safe?  I couldn't find any real code that worries about
this.  The code in AppleRAIDSet.cpp in AppleRAID is pretty
typical:
   IOWorkLoop * AppleRAIDSet::getWorkLoop(void)
   {
       // Create a WorkLoop if it has not already been done.
       if (arSetWorkLoop == 0) {
           arSetWorkLoop = IOWorkLoop::workLoop();
       }

       return arSetWorkLoop;
   }

Is there a race condition where two different threads could call
getWorkLoop(), resulting in the unwanted creation of two
different IOWorkLoop objects?
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