// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Tries to extract the top object of the stack.
// If the stack is empty, the method returns nullptr.
T* Pop() {
T* node;
int waitCount = 0; // Used for back off.
time_ = ThreadUtils::GetSystemTime();
while(true) {
HeadType oldHead = Memory::ReadValue(&head_);
node = oldHead.GetFirst();
if(node == nullptr) {
return nullptr; // The stack is empty;
}
// Is 'head' still the same?
if(oldHead == Memory::ReadValue(&head_)) {
HeadType newHead = HeadType(oldHead.GetCount() - 1, node->Next);
if(CompareExchange(oldHead, newHead)) {
return node; // The head was successfully updated.
}
}
if((++waitCount % 50) == 0) {
// Give threads with a lower priority a chance to run.
ThreadUtils::SwitchToThread();
}
else {
// Backoff.
for(int i = 0; i < waitCount; i++) {
ThreadUtils::Wait();
}
}
}
}
U32 Interlocked::Add(U32 * addr, U32 value)
{
volatile U32 addrValue,sum;
do
{
addrValue = *addr;
sum = addrValue + value;
if(CompareExchange(addr,sum,addrValue) == addrValue)
return sum;
}while(true);
}
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Tries to insert an object in the stack.
// If the maximum number of objects is reached, the object
// isn't inserted anymore and the method returns the address of the object.
// If the object could be inserted, the method returns nullptr.
T* Push(T* node) {
int waitCount = 0; // Used for back off.
time_ = ThreadUtils::GetSystemTime();
while(true) {
HeadType oldHead = Memory::ReadValue(&head_);
if(oldHead.GetCount() >= maxObjects_) {
return node; // The stack has reached the maximum number of objects.
}
// Set the new head of the stack and update the oldest location.
HeadType newHead = HeadType(oldHead.GetCount() + 1, node);
// Is 'head' still the same?
if(oldHead == Memory::ReadValue(&head_)) {
// Link the node to the current head of the stack.
node->Next = oldHead.GetFirst();
if(CompareExchange(oldHead, newHead)) {
T* temp = newHead.GetFirst();
temp->Next = temp->Next;
return nullptr; // The head was successfully updated.
}
}
if((++waitCount % 50) == 0) {
// Give threads with a lower priority a chance to run.
ThreadUtils::SwitchToThread();
}
else {
// Back off.
for(int i = 0; i < waitCount; i++) {
ThreadUtils::Wait();
}
}
}
}
