Segment成员变量
long long m_index;
记录该segment的索引号。
int* volatile m_state;
状态数组，标识所对应的元素节点的状态，默认值为0，如果该元素节点添加了值，则标记为1。
T* volatile m_array;
队列元素存储空间的指针。
Segment* volatile m_next;
指向下一个segment的指针。
volatile long m_high;
标识在当前segment，元素最后添加的索引值，初始值为-1，如果该segment被填满了，则该值为SEGMENT_SIZE – 1。
volatile long m_low;
标识在当前segment，元素最后取出位置的索引值，初始值为0，如果该segment一个都没有取走元素，则该值为0。如果m_low >m_high,表示该segment为空。
Segment成员函数
void Grow(Segment* volatile* tail)
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void Grow(Segment* volatile* tail){ Segment* segment = new Segment(m_index + 1); m_next = segment; *tail = m_next;} |
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创建下一个segment，并将tail指针指向新创建的segment； |
bool TryAppend(T value, Segment* volatile * tail)
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bool TryAppend(T value, Segment* volatile * tail){ if (m_high >= SEGMENT_SIZE - 1) { return false; } int index = SEGMENT_SIZE; index = InterlockedIncrement(&m_high); if (index <= SEGMENT_SIZE - 1) { m_array[index] = value; m_state[index] = 1; } if (index == SEGMENT_SIZE - 1) { Grow(tail); } return (index <= SEGMENT_SIZE - 1);} |
往当前segment里面，增加一个元素，如果添加满了，就创建下一个segment。
bool TryPeek(T* result)
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bool TryPeek(T* result){ int low = GetLow(); if (low > GetHigh()) { return false; } DNetSpinWait wait; while (m_state[low] == 0) { wait.SpinOnce(); } *result = m_array[low]; return true;} |
如果segment为空，返回false，否则，返回low所在位置的值。
bool TryRemove(T* result, Segment* volatile * head)
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bool TryRemove(T* result, Segment* volatile * head){ DNetSpinWait wait; int low = GetLow(); for (int i = GetHigh(); low <= i; i = GetHigh()) { if (InterlockedCompareExchange(&m_low, low + 1, low) == low) { DNetSpinWait wait2; while (m_state[low] == 0) { wait2.SpinOnce(); } *result = m_array[low]; if ((low + 1) >= SEGMENT_SIZE) { wait2.Reset(); while (m_next == NULL) { wait2.SpinOnce(); } *head = m_next; } return true; } wait.SpinOnce(); low = GetLow(); } result = NULL; return false;} |
这是最复杂的一个方法。利用了InterlockedCompareExchange方法，该方法的解释：
LONG __cdecl InterlockedCompareExchange(
__inout LONG volatile* Destination,
__in LONG Exchange,
__in LONG Comparand
);
Parameters
Destination
A pointer to the destination value. The sign is ignored.
Exchange
The exchange value. The sign is ignored.
Comparand
The value to compare to Destination. The sign is ignored.
Return Value
The function returns the initial value of the Destination parameter.
通过自旋来保证线程同步。
int GetHigh()
{
return min(m_high, SEGMENT_SIZE - 1);
}
bool IsEmpty()
{
return m_low > m_high;
}
int GetLow()
{
return min(m_low, SEGMENT_SIZE);
}
Segment* GetNext()
{
return m_next;
}
long long GetIndex()
{
return m_index;
}