160 lines
4.6 KiB
Go
160 lines
4.6 KiB
Go
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/*
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* Copyright (C) THL A29 Limited, a Tencent company. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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*/
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package lockfree
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import (
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"fmt"
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"runtime"
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"sync/atomic"
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"time"
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)
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// Producer 生产者
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// 核心方法是Write，通过调用Write方法可以将对象写入到队列中
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type Producer[T any] struct {
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seqer *sequencer
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rbuf *ringBuffer[T]
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blocks blockStrategy
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capacity uint64
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status int32
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}
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func newProducer[T any](seqer *sequencer, rbuf *ringBuffer[T], blocks blockStrategy) *Producer[T] {
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return &Producer[T]{
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seqer: seqer,
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rbuf: rbuf,
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blocks: blocks,
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capacity: rbuf.cap(),
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status: READY,
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}
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}
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func (q *Producer[T]) start() error {
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if atomic.CompareAndSwapInt32(&q.status, READY, RUNNING) {
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return nil
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}
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return fmt.Errorf(StartErrorFormat, "Producer")
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}
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// Write 对象写入核心逻辑
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// 首先会从序号产生器中获取一个序号，该序号由atomic自增，不会重复；
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// 然后通过&运算获取该序号应该放入的位置pos；
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// 通过循环的方式，判断对应pos位置是否可以写入内容，这个判断是通过available数组判断的；
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// 如果无法写入则持续循环等待，直到可以写入为止，此处基于一种思想即写入的实时性，写入操作不需要等太久，因此此处是没有阻塞的，
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// 仅仅通过调度让出的方式，进行一部分cpu让渡，防止持续占用cpu资源
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// 获取到写入资格后将内容写入到ringbuffer，同时更新available数组，并且调用release，以便于释放消费端的阻塞等待
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func (q *Producer[T]) Write(v T) error {
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if q.closed() {
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return ClosedError
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}
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next := q.seqer.wc.increment()
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for {
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// 判断是否可以写入
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r := atomic.LoadUint64(&q.seqer.rc) - 1
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if next <= r+q.capacity {
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// 可以写入数据，将数据写入到指定位置
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q.rbuf.write(next-1, v)
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// 释放，防止消费端阻塞
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q.blocks.release()
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return nil
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}
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runtime.Gosched()
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// 再次判断是否已关闭
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if q.closed() {
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return ClosedError
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}
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}
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}
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// WriteWindow 写入窗口
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// 描述当前可写入的状态，如果不能写入则返回零值，如果可以写入则返回写入窗口大小
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// 由于执行时不加锁，所以该结果是不可靠的，仅用于在并发环境很高的情况下，进行丢弃行为
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func (q *Producer[T]) WriteWindow() int {
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next := q.seqer.wc.atomicLoad() + 1
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r := atomic.LoadUint64(&q.seqer.rc)
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if next < r+q.capacity {
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return int(r + q.capacity - next)
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}
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return -int(next - (r + q.capacity))
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}
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// WriteTimeout 在写入的基础上设定一个时间，如果时间到了仍然没有写入则会放弃本次写入，返回写入的位置和false
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// 使用方需要调用 WriteByCursor 来继续写入该位置，因为位置已经被占用，是必须要写的，不能跳跃性写入
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// 在指定时间内写入成功会返回true
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// 三个返回项：写入位置、是否写入成功及是否有error
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func (q *Producer[T]) WriteTimeout(v T, timeout time.Duration) (uint64, bool, error) {
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if q.closed() {
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return 0, false, ClosedError
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}
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next := q.seqer.wc.increment()
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// 先尝试写数据 (failfast)
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ok := q.writeByCursor(v, next)
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if ok {
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return next, true, nil
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}
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// 创建定时器
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waiter := time.NewTimer(timeout)
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defer waiter.Stop()
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for {
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select {
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case <-waiter.C:
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// 超时触发，执行到此处表示未写入，返回对应结果即可
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return next, false, nil
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default:
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ok = q.writeByCursor(v, next)
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if ok {
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return next, true, nil
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}
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runtime.Gosched()
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}
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if q.closed() {
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return 0, false, ClosedError
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}
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}
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}
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// WriteByCursor 根据游标写入内容，wc是调用 WriteTimeout 方法返回false时对应的写入位置，
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// 该位置有严格的含义，不要随意填值，否则会造成整个队列异常
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// 函数返回值：是否写入成功和是否存在error，若返回false表示写入失败，可以继续调用重复写入
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func (q *Producer[T]) WriteByCursor(v T, wc uint64) (bool, error) {
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if q.closed() {
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return false, ClosedError
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}
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return q.writeByCursor(v, wc), nil
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}
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func (q *Producer[T]) writeByCursor(v T, wc uint64) bool {
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// 判断是否可以写入
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r := atomic.LoadUint64(&q.seqer.rc) - 1
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if wc <= r+q.capacity {
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// 可以写入数据，将数据写入到指定位置
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q.rbuf.write(wc-1, v)
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// 释放，防止消费端阻塞
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q.blocks.release()
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// 返回写入成功标识
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return true
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}
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return false
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}
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func (q *Producer[T]) close() error {
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if atomic.CompareAndSwapInt32(&q.status, RUNNING, READY) {
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return nil
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}
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return fmt.Errorf(CloseErrorFormat, "Producer")
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}
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func (q *Producer[T]) closed() bool {
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return atomic.LoadInt32(&q.status) == READY
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}
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