Function

OSAddAtomic

32-bit add operation, performed atomically with respect to all devices that participate in the coherency architecture of the platform.

Declaration

SInt32 OSAddAtomic(SInt32 amount, volatile SInt32 *address);

Parameters

amount

The amount to add.

address

The 4-byte aligned address of the value to update atomically.

Return Value

The value before the addition

Discussion

The OSAddAtomic function adds the specified amount to the value at the specified address and returns the original value.

This function guarantees atomicity only with main system memory. It is specifically unsuitable for use on noncacheable memory such as that in devices; this function cannot guarantee atomicity, for example, on memory mapped from a PCI device. Previous incarnations of this function incorporated a memory barrier on systems with weakly-ordered memory architectures, but current versions contain no barriers.