ae2cbbf851
While adding some code to clear the Next field when popping from a task stack for safety reasons, the clear was placed outside of a nil pointer check. As a result, (*internal/task.Stack).Pop panicked when the Stack is empty.
98 строки
1,9 КиБ
Go
98 строки
1,9 КиБ
Go
package task
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const asserts = false
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// Queue is a FIFO container of tasks.
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// The zero value is an empty queue.
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type Queue struct {
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head, tail *Task
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}
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// Push a task onto the queue.
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func (q *Queue) Push(t *Task) {
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if asserts && t.Next != nil {
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panic("runtime: pushing a task to a queue with a non-nil Next pointer")
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}
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if q.tail != nil {
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q.tail.Next = t
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}
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q.tail = t
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t.Next = nil
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if q.head == nil {
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q.head = t
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}
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}
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// Pop a task off of the queue.
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func (q *Queue) Pop() *Task {
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t := q.head
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if t == nil {
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return nil
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}
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q.head = t.Next
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if q.tail == t {
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q.tail = nil
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}
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t.Next = nil
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return t
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}
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// Append pops the contents of another queue and pushes them onto the end of this queue.
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func (q *Queue) Append(other *Queue) {
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if q.head == nil {
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q.head = other.head
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} else {
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q.tail.Next = other.head
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}
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q.tail = other.tail
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other.head, other.tail = nil, nil
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}
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// Stack is a LIFO container of tasks.
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// The zero value is an empty stack.
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// This is slightly cheaper than a queue, so it can be preferable when strict ordering is not necessary.
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type Stack struct {
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top *Task
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}
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// Push a task onto the stack.
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func (s *Stack) Push(t *Task) {
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if asserts && t.Next != nil {
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panic("runtime: pushing a task to a stack with a non-nil Next pointer")
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}
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s.top, t.Next = t, s.top
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}
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// Pop a task off of the stack.
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func (s *Stack) Pop() *Task {
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t := s.top
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if t != nil {
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s.top = t.Next
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t.Next = nil
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}
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return t
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}
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// tail follows the chain of tasks.
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// If t is nil, returns nil.
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// Otherwise, returns the task in the chain where the Next field is nil.
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func (t *Task) tail() *Task {
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if t == nil {
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return nil
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}
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for t.Next != nil {
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t = t.Next
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}
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return t
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}
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// Queue moves the contents of the stack into a queue.
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// Elements can be popped from the queue in the same order that they would be popped from the stack.
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func (s *Stack) Queue() Queue {
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head := s.top
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s.top = nil
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return Queue{
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head: head,
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tail: head.tail(),
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}
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}
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