zeus
52 lines
1.2 KiB
Swift
52 lines
1.2 KiB
Swift
import Dispatch
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/// A ReadWriteBox grants multiple readers and single-writer guarantees on a
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/// value. It is backed by a concurrent DispatchQueue.
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@propertyWrapper
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final class ReadWriteBox<T> {
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private var _wrappedValue: T
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private var queue: DispatchQueue
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var wrappedValue: T {
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get { read { $0 } }
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set { update { $0 = newValue } }
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}
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var projectedValue: ReadWriteBox<T> { self }
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init(wrappedValue: T) {
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_wrappedValue = wrappedValue
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queue = DispatchQueue(label: "GRDB.ReadWriteBox", attributes: [.concurrent])
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}
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func read<U>(_ block: (T) throws -> U) rethrows -> U {
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try queue.sync {
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try block(_wrappedValue)
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}
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}
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func update<U>(_ block: (inout T) throws -> U) rethrows -> U {
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try queue.sync(flags: [.barrier]) {
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try block(&_wrappedValue)
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}
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}
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}
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extension ReadWriteBox where T: Numeric {
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@discardableResult
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func increment() -> T {
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update { n in
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n += 1
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return n
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}
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}
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@discardableResult
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func decrement() -> T {
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update { n in
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n -= 1
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return n
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}
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}
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}
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