What are atomic types in the C language?
Atomic types are those for which reading and writing are guaranteed to happen in a single instruction. More explanation from gnu.org:
24.4.7.2 Atomic Types
To avoid uncertainty about interrupting access to a variable, you can use a particular data type for which access is always atomic:
sig_atomic_t
. Reading and writing this data type is guaranteed to happen in a single instruction, so there’s no way for a handler to run “in the middle” of an access.The type
sig_atomic_t
is always an integer data type, but which one it is, and how many bits it contains, may vary from machine to machine.Data Type:
sig_atomic_t
This is an integer data type. Objects of this type are always accessed atomically.In practice, you can assume that
int
is atomic. You can also assume that pointer types are atomic; that is very convenient. Both of these assumptions are true on all of the machines that the GNU C Library supports and on all POSIX systems we know of.
For even more detail and some C11-specific stuff, check out CppReference.com (no affiliation).