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| /* | ||
| © 2023-present Harald Rudell <[email protected]> (https://haraldrudell.github.io/haraldrudell/) | ||
| All rights reserved | ||
| */ | ||
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| package parl | ||
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| // AwaitableCh is a channel whose only allowed operation is channel receive | ||
| // - AwaitableCh implements a semaphore | ||
| // - AwaitableCh transfers no data, instead channel close is the significant event | ||
| type AwaitableCh <-chan struct{} |
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| @@ -0,0 +1,61 @@ | ||
| /* | ||
| © 2023-present Harald Rudell <[email protected]> (https://haraldrudell.github.io/haraldrudell/) | ||
| All rights reserved | ||
| */ | ||
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| package parl | ||
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| import "sync/atomic" | ||
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| // Awaitable is a semaphore that allows any number of threads to inspect | ||
| // and await an event | ||
| // - one-to-many, happens-before | ||
| // - the synchronization mechanic is closing channel, allowing threads to await | ||
| // multiple events | ||
| // - status can be inspected in a thread-safe manner: isClosed, isAboutToClose | ||
| // allows for race-free consumers | ||
| // - Close is idempotent, panic-free | ||
| // - if atomic.Pointer[Awaitable] is used for retrieval, a cyclic semaphore is achieved | ||
| type Awaitable struct { | ||
| isClosed atomic.Bool | ||
| ch chan struct{} | ||
| } | ||
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| // NewAwaitable returns a one-to-many sempahore | ||
| func NewAwaitable() (awaitable *Awaitable) { | ||
| return &Awaitable{ch: make(chan struct{})} | ||
| } | ||
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| // Ch returns an awaitable channel. Thread-safe | ||
| func (a *Awaitable) Ch() (ch AwaitableCh) { | ||
| return a.ch | ||
| } | ||
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| // isClosed inspects whether the awaitable has been triggered | ||
| // - isClosed indicates that the channel is closed | ||
| // - isAboutToClose indicates that Close has been invoked, | ||
| // but that channel close may still be in progress | ||
| // - the two values are requried to attain race-free consumers | ||
| // - if isClosed is true, isAboutToClose is also true | ||
| // - Thread-safe | ||
| func (a *Awaitable) IsClosed() (isClosed, isAboutToClose bool) { | ||
| select { | ||
| case <-a.ch: | ||
| isClosed = true | ||
| default: | ||
| } | ||
| isAboutToClose = a.isClosed.Load() | ||
| return | ||
| } | ||
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| // Close triggers awaitable by closing the channel | ||
| // - upon return, the channel is guarantee to be closed | ||
| // - idempotent, panic-free, thread-safe | ||
| func (a *Awaitable) Close() (wasClosed bool) { | ||
| if wasClosed = !a.isClosed.CompareAndSwap(false, true); wasClosed { | ||
| <-a.ch // wait to make certain the channel is closed | ||
| return // already closed return | ||
| } | ||
| close(a.ch) | ||
| return // didClose return | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,88 @@ | ||
| /* | ||
| © 2023-present Harald Rudell <[email protected]> (https://haraldrudell.github.io/haraldrudell/) | ||
| All rights reserved | ||
| */ | ||
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| package parl | ||
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| import "sync/atomic" | ||
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| const ( | ||
| CyclicAwaitableClosed = true | ||
| ) | ||
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| // CyclicAwaitable is an awaitable that can be re-initialized | ||
| // - one-to-many, happens-before | ||
| // - the synchronization mechanic is closing channel, allowing threads to await | ||
| // multiple events | ||
| // - status can be inspected in a thread-safe manner: isClosed, isAboutToClose | ||
| // allows for race-free consumers | ||
| // - Close is idempotent, panic-free | ||
| // - if atomic.Pointer[Awaitable] is used for retrieval, a cyclic semaphore is achieved | ||
| type CyclicAwaitable struct { | ||
| p atomic.Pointer[Awaitable] | ||
| } | ||
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| // NewCyclicAwaitable returns an awaitable that can be re-initialized | ||
| // - Init must be invoked prior to use | ||
| func NewCyclicAwaitable() (awaitable *CyclicAwaitable) { | ||
| return &CyclicAwaitable{} | ||
| } | ||
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| // Init sets the initial state of the awaitable | ||
| // - default is not triggered | ||
| // - if argument [task.CyclicAwaitableClosed], initial state | ||
| // is triggered | ||
| func (a *CyclicAwaitable) Init(initiallyClosed ...bool) (a2 *CyclicAwaitable) { | ||
| a2 = a | ||
| var shouldBeClosed = len(initiallyClosed) > 0 && initiallyClosed[0] | ||
| var awaitable = NewAwaitable() | ||
| if shouldBeClosed { | ||
| awaitable.Close() | ||
| } | ||
| a.p.Store(awaitable) | ||
| return | ||
| } | ||
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| // Ch returns an awaitable channel. Thread-safe | ||
| func (a *CyclicAwaitable) Ch() (ch AwaitableCh) { | ||
| return a.p.Load().Ch() | ||
| } | ||
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| // isClosed inspects whether the awaitable has been triggered | ||
| // - isClosed indicates that the channel is closed | ||
| // - isAboutToClose indicates that Close has been invoked, | ||
| // but that channel close may still be in progress | ||
| // - the two values are requried to attain race-free consumers | ||
| // - if isClosed is true, isAboutToClose is also true | ||
| // - Thread-safe | ||
| func (a *CyclicAwaitable) IsClosed() (isClosed, isAboutToClose bool) { | ||
| return a.p.Load().IsClosed() | ||
| } | ||
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| // Close triggers awaitable by closing the channel | ||
| // - upon return, the channel is guarantee to be closed | ||
| // - idempotent, panic-free, thread-safe | ||
| func (a *CyclicAwaitable) Close() (wasClosed bool) { | ||
| return a.p.Load().Close() | ||
| } | ||
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| // Open rearms the awaitable for another cycle | ||
| // - upon return, the channel is guarantee to be open | ||
| // - idempotent, panic-free, thread-safe | ||
| func (a *CyclicAwaitable) Open() (didOpen bool) { | ||
| var openp *Awaitable | ||
| for { | ||
| var ap = a.p.Load() | ||
| var isClosed, _ = ap.IsClosed() | ||
| if !isClosed { | ||
| return // was open return | ||
| } | ||
| if openp == nil { | ||
| openp = NewAwaitable() | ||
| } | ||
| if didOpen = a.p.CompareAndSwap(ap, openp); didOpen { | ||
| return // did open the channel return | ||
| } | ||
| } | ||
| } |
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