atomic_fetch_sub(), atomic_fetch_sub

Atomically subtract the value of an atomic object (C11)

Synopsis:

#include <stdatomic.h>

C atomic_fetch_sub( volatile A *obj,
                    M amount );

C atomic_fetch_sub_explicit( volatile A *obj,
                             M amount,
                             memory_order order );

Arguments:

obj: A pointer to the atomic object (see the atomic_* types) whose value you want to subtract from.
amount: The value you want to subtract from the object. “M” is either the non-atomic type corresponding to A if A is an atomic integer type, or ptrdiff_t if A is an atomic pointer type.
order: (atomic_fetch_sub_explicit() only) The memory_order to use for the operation.

Library:

If the atomic function is lock-free (see atomic_is_lock_free()), no extra library is required.
If the function isn't lock-free, you need to link against libatomic. Use the -l atomic option to qcc to link against this library.

Description:

The atomic_fetch_sub() and atomic_fetch_sub_explicit() functions are generic functions that atomically subtract the given value from the given atomic object. The atomic_fetch_sub() function orders memory access according to memory_order_seq_cst; atomic_fetch_sub_explicit() orders them as specified by order.

Returns:

The previous value of the atomic object. The “C” represents the non-atomic data type that corresponds to the atomic object.

Classification:

C11

Safety:
Cancellation point	No
Interrupt handler	Read the Caveats
Signal handler	Read the Caveats
Thread	Yes

Caveats:

If this function is lock-free (see atomic_is_lock_free()), it's safe to call it from an ISR or signal handler.

atomic_fetch_sub(), atomic_fetch_sub_explicit()