50 lines
1.5 KiB
TypeScript
50 lines
1.5 KiB
TypeScript
const DEFAULT_MAX_CONCURRENT_IMAGE_JOBS = 1
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const MAX_ALLOWED_IMAGE_JOBS = 2
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function readMaxConcurrentImageJobs(): number {
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const configured = Number.parseInt(process.env.IMAGE_PROCESSING_MAX_CONCURRENT || '', 10)
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if (!Number.isFinite(configured)) {
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return DEFAULT_MAX_CONCURRENT_IMAGE_JOBS
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}
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return Math.max(1, Math.min(MAX_ALLOWED_IMAGE_JOBS, configured))
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}
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const maxConcurrentImageJobs = readMaxConcurrentImageJobs()
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let activeImageJobs = 0
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const waitingImageJobs: Array<() => void> = []
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async function acquireImageProcessingSlot(): Promise<void> {
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if (activeImageJobs < maxConcurrentImageJobs) {
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activeImageJobs += 1
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return
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}
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await new Promise<void>((resolve) => waitingImageJobs.push(resolve))
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}
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function releaseImageProcessingSlot(): void {
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const next = waitingImageJobs.shift()
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if (next) {
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// 将当前占用的名额直接交给队首等待者。这里不能先减 active 再让等待者加回，
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// 否则两者之间的新请求可能抢到这个瞬时空位，突破配置的并发上限。
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next()
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return
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}
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activeImageJobs = Math.max(0, activeImageJobs - 1)
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}
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/**
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* 跨请求限制 Sharp 任务数。单个请求内串行并不能阻止多个请求同时解码大图，
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* 所以白底图、预览图和长图处理都必须共用这个进程级门闩。
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*/
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export async function withImageProcessingSlot<T>(task: () => Promise<T>): Promise<T> {
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await acquireImageProcessingSlot()
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try {
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return await task()
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} finally {
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releaseImageProcessingSlot()
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}
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}
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