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Prevent installGlobalExecutor() from running more than once #152

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Jan 24, 2022
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Prevent installGlobalExecutor() from running more than once #152

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6 changes: 6 additions & 0 deletions Sources/JavaScriptEventLoop/JavaScriptEventLoop.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -48,11 +48,15 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
return eventLoop
}()

private static var didInstallGlobalExecutor = false

/// Set JavaScript event loop based executor to be the global executor
/// Note that this should be called before any of the jobs are created.
/// This installation step will be unnecessary after the custom-executor will be introduced officially.
/// See also: https://github.com/rjmccall/swift-evolution/blob/custom-executors/proposals/0000-custom-executors.md#the-default-global-concurrent-executor
public static func installGlobalExecutor() {
guard !didInstallGlobalExecutor else { return }

typealias swift_task_enqueueGlobal_hook_Fn = @convention(thin) (UnownedJob, swift_task_enqueueGlobal_original) -> Void
let swift_task_enqueueGlobal_hook_impl: swift_task_enqueueGlobal_hook_Fn = { job, original in
JavaScriptEventLoop.shared.enqueue(job)
Expand All @@ -70,6 +74,8 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
JavaScriptEventLoop.shared.enqueue(job)
}
swift_task_enqueueMainExecutor_hook = unsafeBitCast(swift_task_enqueueMainExecutor_hook_impl, to: UnsafeMutableRawPointer?.self)

didInstallGlobalExecutor = true
}

private func enqueue(_ job: UnownedJob, withDelay nanoseconds: UInt64) {
Expand Down