Fix image download queue not respecting FIFO order

app/src/main/kotlin/com/hippo/ehviewer/spider/SpiderQueen.kt

@@ -504,7 +504,6 @@ class SpiderQueen private constructor(val galleryInfo: GalleryInfo) : CoroutineS
         private val showKeyLock = Mutex()
         private val mDownloadDelay = Settings.downloadDelay.milliseconds
         private val downloadTimeout = Settings.downloadTimeout.seconds
-        private val delayLock = Mutex()
         private var lastRequestTime = TimeSource.Monotonic.markNow()
         var isDownloadMode = false
             private set
@@ -541,13 +540,6 @@ class SpiderQueen private constructor(val galleryInfo: GalleryInfo) : CoroutineS
             if (currentJob?.isActive != true) {
                 mFetcherJobMap[index] = launch {
                     runCatching {
-                        if (!force && index in mSpiderDen) {
-                            return@runCatching updatePageState(index, STATE_FINISHED)
-                        }
-                        delayLock.withLock {
-                            delay(mDownloadDelay - lastRequestTime.elapsedNow())
-                            lastRequestTime = TimeSource.Monotonic.markNow()
-                        }
                         mSemaphore.withPermit {
                             doInJob(index, force, orgImg, skipHath)
                         }
@@ -584,7 +576,6 @@ class SpiderQueen private constructor(val galleryInfo: GalleryInfo) : CoroutineS
                     ?: getPTokenFromInternet(index)
                     ?: getPTokenFromMultiPageViewer(index)
             }
-            updatePageState(index, STATE_DOWNLOADING)
             val previousPToken: String?
             val pToken: String
             pTokenLock.withLock {
@@ -592,13 +583,20 @@ class SpiderQueen private constructor(val galleryInfo: GalleryInfo) : CoroutineS
                     if (mSpiderInfo.pTokenMap[index] == TOKEN_FAILED) {
                         mSpiderInfo.pTokenMap.remove(index)
                     }
+                } else if (index in mSpiderDen) {
+                    return updatePageState(index, STATE_FINISHED)
                 }
                 pToken = getPToken(index)
                     ?: return updatePageState(index, STATE_FAILED, PTOKEN_FAILED_MESSAGE).also {
                         mSpiderInfo.pTokenMap[index] = TOKEN_FAILED
                     }
                 previousPToken = getPToken(index - 1)
+
+                // The lock for delay should be acquired before anything else to maintain FIFO order
+                delay(mDownloadDelay - lastRequestTime.elapsedNow())
+                lastRequestTime = TimeSource.Monotonic.markNow()
             }
+            updatePageState(index, STATE_DOWNLOADING)
 
             var skipHathKey: String? = null
             var originImageUrl: String? = null