Fabien Niñoles wrote:
Quote from http://msdn2.microsoft.com/en-us/library/s1sb61xd.aspx: "Assigning to a static local variable is not thread safe and is not recommended as a programming practice."
Although this isn't very concise wording (IIRC, the standard says that it should work for literals assigned to PODs) it seems clear that it won't work for non-PODs...
The example below the warning clearly show up what they mean, and it's really a concurrency situation where two threads access the same object.
I don't see how the quoted example has any bearing on MT issues. It is a single threaded program.
So, yes, this is a bad practice, and it is clearly not thread-safe, even for POD:
I should have been clearer. The standard sais that *initializing* a POD is not a problem because that is done before any threads have a chance to race against each other (typically when the binary is loaded into memory). In the example, the second assignment to the POD is indeed a problem because it must happen at runtime. What I meant with my original statement is the following: class NonPod { public: NonPod() { /* ... */ } }; class Whatever { public: static int & GetPodInstance() { static int podInstance = 42; return podInstance; } static NonPod & GetNonPodInstance() { static NonPod nonPodInstance; return nonPodInstance; } }; When multiple threads are present, there's no race condition when more than one of them call GetPodInstance(). Clearly there is one when they call GetNonPodInstance() because NonPod::NonPod() will non run before the first call... -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header.