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125 lines (104 loc) · 4.23 KB
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// This file contains the job queue implementation for JavaScriptEventLoop.
// It manages job insertion and execution based on priority, ensuring thread safety and performance.
import _CJavaScriptEventLoop
import os.lock
/// Represents the state of the job queue.
@available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
struct QueueState: Sendable {
/// The head of the job queue.
fileprivate var headJob: UnownedJob? = nil
/// Indicates if the queue is actively processing jobs.
fileprivate var isSpinning: Bool = false
}
@available(macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0, *)
extension JavaScriptEventLoop {
/// A lock to synchronize queue access using `os_unfair_lock` for lightweight thread safety.
private static var queueLock = os_unfair_lock_s()
/// Inserts a job into the queue and ensures jobs are processed.
/// - Parameter job: The job to add to the queue.
func insertJobQueue(job newJob: UnownedJob) {
os_unfair_lock_lock(&JavaScriptEventLoop.queueLock)
defer { os_unfair_lock_unlock(&JavaScriptEventLoop.queueLock) }
insertJob(newJob)
if !queueState.isSpinning {
queueState.isSpinning = true
JavaScriptEventLoop.shared.queueMicrotask {
self.runAllJobs()
}
}
}
/// Inserts a job into the queue at the correct priority position.
/// - Parameter job: The job to insert into the queue.
private func insertJob(_ newJob: UnownedJob) {
var current = queueState.headJob
var previous: UnownedJob? = nil
while let cur = current, cur.rawPriority >= newJob.rawPriority {
previous = cur
current = cur.nextInQueue().pointee
}
newJob.nextInQueue().pointee = current
if let prev = previous {
prev.nextInQueue().pointee = newJob
} else {
queueState.headJob = newJob
}
}
/// Processes all jobs in the queue until it is empty.
func runAllJobs() {
assert(queueState.isSpinning, "runAllJobs called while queueState.isSpinning is false.")
while let job = claimNextFromQueue() {
executeJob(job)
}
queueState.isSpinning = false
}
/// Executes a specific job.
/// - Parameter job: The job to execute.
private func executeJob(_ job: UnownedJob) {
#if compiler(>=5.9)
job.runSynchronously(on: self.asUnownedSerialExecutor())
#else
job._runSynchronously(on: self.asUnownedSerialExecutor())
#endif
}
/// Removes and returns the next job from the queue.
/// - Returns: The next job in the queue, or `nil` if the queue is empty.
func claimNextFromQueue() -> UnownedJob? {
os_unfair_lock_lock(&JavaScriptEventLoop.queueLock)
defer { os_unfair_lock_unlock(&JavaScriptEventLoop.queueLock) }
guard let job = queueState.headJob else { return nil }
queueState.headJob = job.nextInQueue().pointee
return job
}
}
@available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
fileprivate extension UnownedJob {
/// Converts the job to its internal implementation.
/// - Returns: A raw pointer to the job's internal structure.
private func asImpl() -> UnsafeMutablePointer<_CJavaScriptEventLoop.Job> {
unsafeBitCast(self, to: UnsafeMutablePointer<_CJavaScriptEventLoop.Job>.self)
}
/// The job's priority flags.
var flags: JobFlags {
JobFlags(bits: asImpl().pointee.Flags)
}
/// The raw priority value of the job.
var rawPriority: UInt32 {
flags.priority
}
/// Retrieves a pointer to the next job in the queue.
/// - Returns: A pointer to the next job, or `nil` if there are no further jobs.
func nextInQueue() -> UnsafeMutablePointer<UnownedJob?> {
withUnsafeMutablePointer(to: &asImpl().pointee.SchedulerPrivate.0) { rawNextJobPtr in
UnsafeMutableRawPointer(rawNextJobPtr).bindMemory(to: UnownedJob?.self, capacity: 1)
}
}
}
/// Represents job flags including priority.
fileprivate struct JobFlags {
/// The raw bit representation of the flags.
var bits: UInt32 = 0
/// Extracts the priority value from the flags.
var priority: UInt32 {
(bits & 0xFF00) >> 8
}
}