Fix off-screen fetcher jobs blocking decode queue

app/src/main/kotlin/com/hippo/ehviewer/gallery/ArchivePageLoader.kt

@@ -143,6 +143,10 @@ class ArchivePageLoader(
     override val isReady: Boolean
         get() = size != 0
 
+    override fun onCancelRequest(index: Int) {
+        jobs[index]?.cancel()
+    }
+
     override val title by lazy {
         FileUtils.getNameFromFilename(file.name)!!
     }

app/src/main/kotlin/com/hippo/ehviewer/gallery/EhPageLoader.kt

@@ -66,6 +66,10 @@ class EhPageLoader(private val mGalleryInfo: GalleryInfo, startPage: Int) :
     override val isReady: Boolean
         get() = ::mSpiderQueen.isInitialized && mSpiderQueen.isReady
 
+    override fun onCancelRequest(index: Int) {
+        mSpiderQueen.cancelRequest(index)
+    }
+
     override fun onGetPages(pages: Int) {}
 
     override fun onGet509(index: Int) {}

app/src/main/kotlin/com/hippo/ehviewer/gallery/PageLoader.kt

@@ -109,6 +109,12 @@ abstract class PageLoader {
 
     protected abstract fun onForceRequest(index: Int, orgImg: Boolean)
 
+    fun cancelRequest(index: Int) {
+        onCancelRequest(index)
+    }
+
+    protected abstract fun onCancelRequest(index: Int)
+
     fun notifyPageWait(index: Int) {
         pages[index].reset()
     }

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

@@ -281,6 +281,10 @@ class SpiderQueen private constructor(val galleryInfo: GalleryInfo) : CoroutineS
         }
     }
 
+    fun cancelRequest(index: Int) {
+        mWorkerScope.cancelDecode(index)
+    }
+
     fun preloadPages(pages: List<Int>, pair: Pair<Int, Int>) {
         mWorkerScope.updateRAList(pages, pair)
     }
@@ -503,6 +507,10 @@ class SpiderQueen private constructor(val galleryInfo: GalleryInfo) : CoroutineS
         var isDownloadMode = false
             private set
 
+        fun cancelDecode(index: Int) {
+            decoder.cancel(index)
+        }
+
         @Synchronized
         fun enterDownloadMode() {
             if (isDownloadMode) return

app/src/main/kotlin/com/hippo/ehviewer/ui/reader/PagerItem.kt

@@ -61,6 +61,11 @@ fun PagerItem(
             }
         }
     }
+    DisposableEffect(Unit) {
+        onDispose {
+            pageLoader.cancelRequest(page.index)
+        }
+    }
     val defaultError = stringResource(id = R.string.decode_image_error)
     when (val state = page.statusObserved) {
         is PageStatus.Queued, is PageStatus.Loading -> {