Function

OSTestAndSet

Bit test and set operation, performed atomically with respect to all devices that participate in the coherency architecture of the platform.

Declaration

Boolean OSTestAndSet(UInt32 bit, volatile UInt8 *startAddress);

Parameters

bit

The bit number in the range 0 through 7.

startAddress

The address of the byte to update atomically.

Return Value

true if the bit was already set, false otherwise.

Discussion

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. Additionally, this function incorporates a memory barrier on systems with weakly-ordered memory architectures.

The OSTestAndSet function sets a single bit in a byte at a specified address. It returns true if the bit was already set, false otherwise.