Starboard Module Reference: atomic.h

  • This document details a set of atomic integer operations intended for lightweight synchronization or as components in more complex synchronization systems.

  • Direct use of these atomic operations is discouraged unless absolutely necessary for performance, due to their complexity and the detailed understanding of supported architectures required.

  • The document defines SbAtomic64 for 64-bit operations (available on 64-bit processors) and SbAtomicPtr for pointer-sized operations (either 32-bit or 64-bit).

  • Several functions are outlined, including variations of CompareAndSwap, Exchange, and Increment, with options for memory ordering like Acquire, Release, and Barrier semantics.

  • The functions are provided as low level, and are useful for implementing higher-level synchronization operations like spinlocks, mutexes and condition-variables.

Defines a set of atomic integer operations that can be used as lightweight synchronization or as building blocks for heavier synchronization primitives. Their use is very subtle and requires detailed understanding of the behavior of supported architectures, so their direct use is not recommended except when rigorously deemed absolutely necessary for performance reasons.

Typedefs

SbAtomic64

64-bit atomic operations (only available on 64-bit processors).

Definition

typedef int64_t SbAtomic64

SbAtomicPtr

Pointer-sized atomic operations. Forwards to either 32-bit or 64-bit functions as appropriate.

Definition

typedef SbAtomic32 SbAtomicPtr

Functions

SbAtomicAcquire_CompareAndSwap

These following lower-level operations are typically useful only to people implementing higher-level synchronization operations like spinlocks, mutexes, and condition-variables. They combine CompareAndSwap(), a load, or a store with appropriate memory-ordering instructions. "Acquire" operations ensure that no later memory access can be reordered ahead of the operation. "Release" operations ensure that no previous memory access can be reordered after the operation. "Barrier" operations have both "Acquire" and "Release" semantics. A SbAtomicMemoryBarrier() has "Barrier" semantics, but does no memory access.

Declaration

static SbAtomic32 SbAtomicAcquire_CompareAndSwap(volatile SbAtomic32 *ptr, SbAtomic32 old_value, SbAtomic32 new_value)

SbAtomicBarrier_Increment

Same as SbAtomicNoBarrier_Increment, but with a memory barrier.

Declaration

static SbAtomic32 SbAtomicBarrier_Increment(volatile SbAtomic32 *ptr, SbAtomic32 increment)

SbAtomicNoBarrier_CompareAndSwap

Atomically execute: result = ptr; if (ptr == old_value) *ptr = new_value; return result;

I.e., replace "ptr" with "new_value" if "ptr" used to be "old_value". Always return the old value of "*ptr"

This routine implies no memory barriers.

Declaration

static SbAtomic32 SbAtomicNoBarrier_CompareAndSwap(volatile SbAtomic32 *ptr, SbAtomic32 old_value, SbAtomic32 new_value)

SbAtomicNoBarrier_Exchange

Atomically store new_value into *ptr, returning the previous value held in *ptr. This routine implies no memory barriers.

Declaration

static SbAtomic32 SbAtomicNoBarrier_Exchange(volatile SbAtomic32 *ptr, SbAtomic32 new_value)

SbAtomicNoBarrier_Increment

Atomically increment *ptr by "increment". Returns the new value of *ptr with the increment applied. This routine implies no memory barriers.

Declaration

static SbAtomic32 SbAtomicNoBarrier_Increment(volatile SbAtomic32 *ptr, SbAtomic32 increment)

SbAtomicRelease_CompareAndSwap8

Overloaded functions for Atomic8.

Declaration

static SbAtomic8 SbAtomicRelease_CompareAndSwap8(volatile SbAtomic8 *ptr, SbAtomic8 old_value, SbAtomic8 new_value)