Thread safe is a flag which is put on memory object saying this can be accessed by more than one thread at a time. I would suggest you read below blog for the explanation
Why CMEMTHREAD Wait Type Occurs?
Quoting
MEMOBJ acts like a HEAP in SQL Server engine, so SQL
Server calls CreateMemoryObject function instead of HeapCreate, which is managed by SQL Server Memory Manager. CMEMOBJ is
responsible to handle any kind of activity in SQL Server such as Alloc, Free, ReAlloc, Size and Validate.
Remember that CMEMOBJ is also not thread safe, therefore only one thread can access it at same time, it is similar to HEAP_NO_SERIALIZE in
Windows.
CMEMTHREAD acts like a serializer around CMEMOBJ, the SQL
Server creates a memory object with a thread safe flag and CreateMemoryObject will return a pointer to CMEMTHREAD instead
of the CMEMOBJ. By overriding some underling Windows methods, SQL Server is able to share a memory object among any thread and make it thread safe object.
Cheers,
Shashank
Please mark this reply as answer if it solved your issue or vote as helpful if it helped so that other forum members can benefit from it
My TechNet Wiki Articles
MVP
what's actually CMEMTHREAD
