He-Pin opened a new issue, #3225:
URL: https://github.com/apache/pekko/issues/3225
### Motivation
`FlowOps.delay` 的延迟精度硬编码为 10ms（`DelayPrecisionMS = 10`），实际延迟粒度还依赖
`scheduleOnce` 精度和上游发射时机，可能导致实际延迟与用户配置的 delay 值存在较大偏差。
### 当前代码行为
`Ops.scala` 中 Delay 阶段实现：
```scala
// Ops.scala:2025
private val DelayPrecisionMS = 10
// Ops.scala:2141
def nextElementWaitTime(): Long = ...
```
当 buffer 非空且下游 pull 时，计算 `waitTime`，仅在 `waitTime <= DelayPrecisionMS` 时立即
push。10ms 的硬编码精度意味着：
- 小于 10ms 的 delay 可能无法精确控制
- 实际精度依赖系统调度器（`scheduleOnce`）的精度
- 上游发射频率也会影响实际延迟
### 预期行为
延迟精度应可配置或自适应，至少文档应明确说明精度限制。
### 代码证据
-
`stream/src/main/scala/org/apache/pekko/stream/impl/fusing/Ops.scala:2023-2153`
— Delay 阶段完整实现
- `stream/src/main/scala/org/apache/pekko/stream/impl/fusing/Ops.scala:2025`
— `DelayPrecisionMS = 10` 硬编码
### 复现方式
```scala
val start = System.nanoTime()
Source(List(1, 2, 3))
.delay(50.millis, DelayOverflowStrategy.backpressure)
.map { elem =>
val elapsed = (System.nanoTime() - start) / 1e6
println(s"$elem at ${elapsed}ms")
elem
}
.runWith(Sink.ignore)
// 观察实际延迟是否与配置的 50ms 匹配
```
### 影响范围
- 模块：`pekko-stream`
- 影响需要精确延迟控制的流处理场景
- 限流、时间窗口等对延迟敏感的使用场景
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