shibd commented on PR #955:
URL: https://github.com/apache/pulsar-client-go/pull/955#issuecomment-1449284692
> > This semaphore can only support acquire or release 1 signal.
>
> Yes. But we can adopt a similar way to handle this case.
>
> For example, if we add a `ch chan bool` field to `memoryLimitController`,
we can implement blocking `ReserveMemory` method like:
>
> ```go
> func (m *memoryLimitController) ReserveMemory(ctx context.Context, size
int64) bool {
> // NOTE: maybe we need to check if m.currentUsage > m.limit first
> currentUsage := atomic.AddInt64(&m.currentUsage, size)
> for currentUsage > m.limit {
> select {
> case <-m.ch:
> currentUsage = atomic.LoadInt64(&m.currentUsage)
> case <-ctx.Done(): // NOTE: Not sure if we need to reset
some fields here
> return false
> }
> }
> return true
> }
>
> func (m *memoryLimitController) ReleaseMemory(size int64) {
> newUsage := atomic.AddInt64(&m.currentUsage, -size)
> // newUsage+size > m.limit means m was blocked in ReserveMemory
method
> if newUsage+size > m.limit && newUsage <= m.limit {
> m.ch <- true
> }
> }
> ```
>
> The code above is not verified yet. But with the channel the code looks
more simple and clear.
This implementation has a problem, and the `broadcasting` cannot be
implemented using channels.
For example:
1. `currentUsage` = 100, `limit` = 100
2. goroutine `1` call `ReseveMemory(10)`, it will blocked.
3. goroutine `2` call `ReseveMemory(10)`, it will blocked.
4. goroutine `3` call `ReleaseMemory(20)`, it only wake one goroutine(1 or
2). The expectation is that both are woken up and return true.
// NOTE: maybe we need to check if m.currentUsage > m.limit first
Like this note. If we want to handle this case, we may need to introduce a
variable `waitNum`. So I feel like it's complicated to implement
`mem_controller_limit`, and it's better to introduce `channel_cond`.
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