taskgroup: add an explicit Throttle type #6
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This generalizes the functionality of the Group.Limit method, which has been rewritten to use the new Throttle type internally. A caller wishing to share capacity among multiple Groups can explicitly construct a throttle and use its Limit method to produce start functions for each Group separately.
creachadair
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| // Enter blocks until a slot is available in t, then returns a [Leaver] that | ||
| // the caller must execute to return the slot when it is no longer in use. | ||
| func (t Throttle) Enter() Leaver { |
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This signature almost looks like context.WithCancel... I don't know if there's anything in that, just noticed and wondering if there's some opportunity to move the two closer together. Probably not, but sharing in case it causes any flash of insight.
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It kind of does, but I'm not sure I see the rhyme: WithCancel returns the new context and the CancelFunc, on the principle you ought to be using both. But here you kind of already have to have the Throttle in-hand. Am I missing something?
| if n <= 0 { | ||
| return Throttle{} | ||
| } | ||
| return Throttle{adm: make(chan struct{}, n)} |
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Extremely mild thought: for large limiters, a mutex+cond+uint may be more efficient? More irritating to program, but it's all hidden away neatly, so maybe?...
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I did some testing on it some while back (before I started using this pattern), and it's actually not—I think the compiler may have some special cases for channel-of-zero-width-values or something.
This generalizes the functionality of the Group.Limit method, which has been
rewritten to use the new Throttle type internally. A caller wishing to share
capacity among multiple Groups can explicitly construct a throttle and use its
Limit method to produce start functions for each Group separately.