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A separate deque with threads to be executed is maintained for each processor. To execute the next thread, the processor gets the first element from the deque (using the "remove first element" deque operation). If the current thread forks, it is put back to the front of the deque ("insert element at front") and a new thread is executed.
The operation of adding an element to the rear of the queue is known as enqueue, and the operation of removing an element from the front is known as dequeue. Other operations may also be allowed, often including a peek or front operation that returns the value of the next element to be dequeued without dequeuing it.
Input: A graph G and a starting vertex root of G. Output: Goal state.The parent links trace the shortest path back to root [9]. 1 procedure BFS(G, root) is 2 let Q be a queue 3 label root as explored 4 Q.enqueue(root) 5 while Q is not empty do 6 v := Q.dequeue() 7 if v is the goal then 8 return v 9 for all edges from v to w in G.adjacentEdges(v) do 10 if w is not labeled as explored then 11 ...
This makes the min-max heap a very useful data structure to implement a double-ended priority queue. Like binary min-heaps and max-heaps, min-max heaps support logarithmic insertion and deletion and can be built in linear time. [3] Min-max heaps are often represented implicitly in an array; [4] hence it's referred to as an implicit data structure.
Representation of a FIFO queue with enqueue and dequeue operations. Depending on the application, a FIFO could be implemented as a hardware shift register, or using different memory structures, typically a circular buffer or a kind of list. For information on the abstract data structure, see Queue (data structure).
procedure BFS(G, v) is create a queue Q enqueue v onto Q mark v while Q is not empty do w ← Q.dequeue() if w is what we are looking for then return w for all edges e in G.adjacentEdges(w) do x ← G.adjacentVertex(w, e) if x is not marked then mark x enqueue x onto Q return null
However, rather than defining the vertex to choose at each step in an imperative way as the one produced by the dequeue operation of a queue, one can define the same sequence of vertices declaratively by the properties of these vertices. That is, a standard breadth-first search is just the result of repeatedly applying this rule:
If its deque is empty, it starts work stealing, explained below. An instruction may cause a thread to die. The behavior in this case is the same as for an instruction that stalls. An instruction may enable another thread. The other thread is pushed onto the bottom of the deque, but the processor continues execution of its current thread.