atomicops_internals_arm_gcc.h

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// Protocol Buffers - Google's data interchange format
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// This file is an internal atomic implementation, use atomicops.h instead.
//
// LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears.

#ifndef GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_ARM_GCC_H_
#define GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_ARM_GCC_H_

namespace google {
namespace protobuf {
namespace internal {

// 0xffff0fc0 is the hard coded address of a function provided by
// the kernel which implements an atomic compare-exchange. On older
// ARM architecture revisions (pre-v6) this may be implemented using
// a syscall. This address is stable, and in active use (hard coded)
// by at least glibc-2.7 and the Android C library.
typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value,
 Atomic32 new_value,
 volatile Atomic32* ptr);
LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg __attribute__((weak)) =
 (LinuxKernelCmpxchgFunc) 0xffff0fc0;

typedef void (*LinuxKernelMemoryBarrierFunc)(void);
LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
 (LinuxKernelMemoryBarrierFunc) 0xffff0fa0;


inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
 Atomic32 old_value,
 Atomic32 new_value) {
 Atomic32 prev_value = *ptr;
 do {
 if (!pLinuxKernelCmpxchg(old_value, new_value,
 const_cast<Atomic32*>(ptr))) {
 return old_value;
 }
 prev_value = *ptr;
 } while (prev_value == old_value);
 return prev_value;
}

inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
 Atomic32 new_value) {
 Atomic32 old_value;
 do {
 old_value = *ptr;
 } while (pLinuxKernelCmpxchg(old_value, new_value,
 const_cast<Atomic32*>(ptr)));
 return old_value;
}

inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
 Atomic32 increment) {
 return Barrier_AtomicIncrement(ptr, increment);
}

inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
 Atomic32 increment) {
 for (;;) {
 // Atomic exchange the old value with an incremented one.
 Atomic32 old_value = *ptr;
 Atomic32 new_value = old_value + increment;
 if (pLinuxKernelCmpxchg(old_value, new_value,
 const_cast<Atomic32*>(ptr)) == 0) {
 // The exchange took place as expected.
 return new_value;
 }
 // Otherwise, *ptr changed mid-loop and we need to retry.
 }
}

inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
 Atomic32 old_value,
 Atomic32 new_value) {
 return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
}

inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
 Atomic32 old_value,
 Atomic32 new_value) {
 return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
}

inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
 *ptr = value;
}

inline void MemoryBarrier() {
 pLinuxKernelMemoryBarrier();
}

inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
 *ptr = value;
 MemoryBarrier();
}

inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
 MemoryBarrier();
 *ptr = value;
}

inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
 return *ptr;
}

inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
 Atomic32 value = *ptr;
 MemoryBarrier();
 return value;
}

inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
 MemoryBarrier();
 return *ptr;
}

} // namespace internal
} // namespace protobuf
} // namespace google

#endif // GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_ARM_GCC_H_