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livetrax/libs/appleutility/CoreAudio/PublicUtility/CAAtomicStack.h

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C++

/*
File: CAAtomicStack.h
Abstract: Part of CoreAudio Utility Classes
Version: 1.1
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*/
#ifndef __CAAtomicStack_h__
#define __CAAtomicStack_h__
#if !defined(__COREAUDIO_USE_FLAT_INCLUDES__)
#include <libkern/OSAtomic.h>
#else
#include <CAAtomic.h>
#endif
#if MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_4
#include <CoreServices/CoreServices.h>
#endif
// linked list LIFO or FIFO (pop_all_reversed) stack, elements are pushed and popped atomically
// class T must implement T *& next().
template <class T>
class TAtomicStack {
public:
TAtomicStack() : mHead(NULL) { }
// non-atomic routines, for use when initializing/deinitializing, operate NON-atomically
void push_NA(T *item)
{
item->next() = mHead;
mHead = item;
}
T * pop_NA()
{
T *result = mHead;
if (result)
mHead = result->next();
return result;
}
bool empty() const { return mHead == NULL; }
T * head() { return mHead; }
// atomic routines
void push_atomic(T *item)
{
T *head_;
do {
head_ = mHead;
item->next() = head_;
} while (!compare_and_swap(head_, item, &mHead));
}
void push_multiple_atomic(T *item)
// pushes entire linked list headed by item
{
T *head_, *p = item, *tail;
// find the last one -- when done, it will be linked to head
do {
tail = p;
p = p->next();
} while (p);
do {
head_ = mHead;
tail->next() = head_;
} while (!compare_and_swap(head_, item, &mHead));
}
T * pop_atomic_single_reader()
// this may only be used when only one thread may potentially pop from the stack.
// if multiple threads may pop, this suffers from the ABA problem.
// <rdar://problem/4606346> TAtomicStack suffers from the ABA problem
{
T *result;
do {
if ((result = mHead) == NULL)
break;
} while (!compare_and_swap(result, result->next(), &mHead));
return result;
}
T * pop_atomic()
// This is inefficient for large linked lists.
// prefer pop_all() to a series of calls to pop_atomic.
// push_multiple_atomic has to traverse the entire list.
{
T *result = pop_all();
if (result) {
T *next = result->next();
if (next)
// push all the remaining items back onto the stack
push_multiple_atomic(next);
}
return result;
}
T * pop_all()
{
T *result;
do {
if ((result = mHead) == NULL)
break;
} while (!compare_and_swap(result, NULL, &mHead));
return result;
}
T* pop_all_reversed()
{
TAtomicStack<T> reversed;
T *p = pop_all(), *next;
while (p != NULL) {
next = p->next();
reversed.push_NA(p);
p = next;
}
return reversed.mHead;
}
static bool compare_and_swap(T *oldvalue, T *newvalue, T **pvalue)
{
#if TARGET_OS_MAC
#if __LP64__
return ::OSAtomicCompareAndSwap64Barrier(int64_t(oldvalue), int64_t(newvalue), (int64_t *)pvalue);
#elif MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
return ::OSAtomicCompareAndSwap32Barrier(int32_t(oldvalue), int32_t(newvalue), (int32_t *)pvalue);
#else
return ::CompareAndSwap(UInt32(oldvalue), UInt32(newvalue), (UInt32 *)pvalue);
#endif
#else
//return ::CompareAndSwap(UInt32(oldvalue), UInt32(newvalue), (UInt32 *)pvalue);
return CAAtomicCompareAndSwap32Barrier(SInt32(oldvalue), SInt32(newvalue), (SInt32*)pvalue);
#endif
}
protected:
T * mHead;
};
#if ((MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_5) && !TARGET_OS_WIN32)
#include <libkern/OSAtomic.h>
class CAAtomicStack {
public:
CAAtomicStack(size_t nextPtrOffset) : mNextPtrOffset(nextPtrOffset) {
/*OSQueueHead h = OS_ATOMIC_QUEUE_INIT; mHead = h;*/
mHead.opaque1 = 0; mHead.opaque2 = 0;
}
// a subset of the above
void push_atomic(void *p) { OSAtomicEnqueue(&mHead, p, mNextPtrOffset); }
void push_NA(void *p) { push_atomic(p); }
void * pop_atomic() { return OSAtomicDequeue(&mHead, mNextPtrOffset); }
void * pop_atomic_single_reader() { return pop_atomic(); }
void * pop_NA() { return pop_atomic(); }
private:
OSQueueHead mHead;
size_t mNextPtrOffset;
};
// a more efficient subset of TAtomicStack using OSQueue.
template <class T>
class TAtomicStack2 {
public:
TAtomicStack2() {
/*OSQueueHead h = OS_ATOMIC_QUEUE_INIT; mHead = h;*/
mHead.opaque1 = 0; mHead.opaque2 = 0;
mNextPtrOffset = -1;
}
void push_atomic(T *item) {
if (mNextPtrOffset < 0) {
T **pnext = &item->next(); // hack around offsetof not working with C++
mNextPtrOffset = (Byte *)pnext - (Byte *)item;
}
OSAtomicEnqueue(&mHead, item, mNextPtrOffset);
}
void push_NA(T *item) { push_atomic(item); }
T * pop_atomic() { return (T *)OSAtomicDequeue(&mHead, mNextPtrOffset); }
T * pop_atomic_single_reader() { return pop_atomic(); }
T * pop_NA() { return pop_atomic(); }
// caution: do not try to implement pop_all_reversed here. the writer could add new elements
// while the reader is trying to pop old ones!
private:
OSQueueHead mHead;
ssize_t mNextPtrOffset;
};
#else
#define TAtomicStack2 TAtomicStack
#endif // MAC_OS_X_VERSION_MAX_ALLOWED && !TARGET_OS_WIN32
#endif // __CAAtomicStack_h__