c++ - Static and global variable in memory

Question

1. Are static variables stored on the stack itself similar to globals? If so, how are they protected to allow for only local class access?

2. In a multi threaded context, is the fear that this memory can be directly accessed by other threads/ kernel? or why cant we use static/global in multi process/ thread enviornment?

Answer 1

Static variables have static storage duration, so they're not normally placed on the stack. The only "protection" for them is that their name has local visibility at compile time. Passing the address of a static variable gives access it it.

Using static/globals in a multithreaded situation has the problem that if one thread modifies a the variable at the same time as another attempts to read it (just for one example) what gets read may be bad data.