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I know that bit-field are compiler dependant, but I haven’t find documentation about thread safety on bit-field with the latest g++ and Visual C++ 2010.
Does the operations on a bit-field member are atomic ?
“Thread safe” is unfortunately a very overloaded term in programming.
If you mean atomic access to bit-fields, the answer is no (at least on all processors I’m aware of). You have atomic access to 32bit memory locations on 32bit machines, but that only means you’ll read or write a whole 32 bit value. This does not mean another thread won’t do the same thing. If you’re looking to stop that you likely want synchronization.
If you mean synchronized access to bit-fields, the answer is also no, unless you wrap your access in a higher level synchronization primitive (which are often built on atomic operations).
In short, the compiler does not provide atomic or synchronized access to bit fields without extra work on your part.
Does that help?
Edit: Dr. Dan Grossman has two nice lectures on atomicity and synchronization I found on UOregon’s CS department page.