Unique ID with ::InterlockedIncrement (VC++)

Using VC++, to get a unique ID that counts upwards, I was wondering whether this is legal in a multi-threaded application?

uint32_t GetNewId() { return ::InterlockedIncrement(&lastId); }

Basically, I am wondering whether InterlockedIncrement just protects the increment, or whether the return value i开发者_运维问答s also guarded against race conditions?

Yes, that is legal - the access which consists of

• read, then
• increment, then
• write, then
• return the incremented value to the caller

will be atomic. Just don't forget that it's 32 bit and can overflow.

Function results are returned in registers and/or stack. Each thread has a separate stack and register set so, yes, this is safe. The InterlockedIncrement will do what it does an its returned value is then no different to any other function result - your function can be interruted and reentered from another thread and will return the correct result for both.

Rgds, Martin

The best way to check is to go to the source.

This function is atomic with respect to calls to other interlocked functions.