Fix image recycle racing

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

@@ -44,14 +44,7 @@ abstract class PageLoader(val gid: Long, var startPage: Int, val size: Int, val
             (OSUtils.appMaxMemory / 3 * 2).toInt()
         },
         sizeOf = { _, v -> v.allocationSize.toInt() },
-        onEntryRemoved = { k, o, n, _ ->
-            if (o.isRecyclable) {
-                n ?: notifyPageWait(k)
-                o.recycle()
-            } else {
-                o.isRecyclable = true
-            }
-        },
+        onEntryRemoved = { k, o, n, _ -> if (o.unpin()) n ?: notifyPageWait(k) },
     )
 
     fun decodePreloadRange(index: Int) = index - 3..index + 3

app/src/main/kotlin/com/hippo/ehviewer/image/Image.kt

@@ -50,10 +50,17 @@ import com.hippo.ehviewer.util.isAtLeastU
 import com.hippo.files.openFileDescriptor
 import com.hippo.files.toUri
 import java.nio.ByteBuffer
+import java.util.concurrent.atomic.AtomicInteger
 import okio.Path
 import splitties.init.appCtx
 
 class Image private constructor(image: CoilImage, private val src: ImageSource) {
+    val refcnt = AtomicInteger(1)
+
+    fun pin() = refcnt.updateAndGet { if (it != 0) it + 1 else 0 } != 0
+
+    fun unpin() = (refcnt.decrementAndGet() == 0).also { if (it) recycle() }
+
     val intrinsicSize = with(image) { IntSize(width, height) }
     val allocationSize = image.size
     val hasQrCode = when (image) {
@@ -66,11 +73,8 @@ class Image private constructor(image: CoilImage, private val src: ImageSource)
         else -> image
     }
 
-    var isRecyclable = true
-
-    @Synchronized
-    fun recycle() {
-        when (val image = innerImage ?: return) {
+    private fun recycle() {
+        when (val image = innerImage!!) {
             is DrawableImage -> src.close()
             is BitmapImage -> image.bitmap.recycle()
         }

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

@@ -11,15 +11,17 @@ import androidx.compose.material3.Button
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.ColorFilter
 import androidx.compose.ui.graphics.ColorMatrix
+import androidx.compose.ui.graphics.painter.Painter
 import androidx.compose.ui.layout.ContentScale
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.style.TextAlign
@@ -42,6 +44,7 @@ import com.hippo.ehviewer.gallery.statusObserved
 import com.hippo.ehviewer.image.Image
 import com.hippo.ehviewer.util.AdsPlaceholderFile
 import eu.kanade.tachiyomi.ui.reader.viewer.CombinedCircularProgressIndicator
+import kotlinx.coroutines.awaitCancellation
 import kotlinx.coroutines.flow.drop
 import moe.tarsin.kt.unreachable
 
@@ -74,32 +77,35 @@ fun PagerItem(
         }
         is PageStatus.Ready -> {
             val image = state.image
-            val painter = remember(image) { image.toPainter() }
-            val grayScale by Settings.grayScale.collectAsState()
-            val invert by Settings.invertedColors.collectAsState()
-            DisposableEffect(image) {
-                image.isRecyclable = false
-                onDispose {
-                    if (image.isRecyclable) {
-                        pageLoader.notifyPageWait(page.index)
-                        image.recycle()
-                    } else {
-                        image.isRecyclable = true
+            var painter by remember { mutableStateOf<Painter?>(null) }
+            LaunchedEffect(image) {
+                if (image.pin()) {
+                    painter = image.toPainter()
+                    try {
+                        awaitCancellation()
+                    } finally {
+                        if (image.unpin()) {
+                            pageLoader.notifyPageWait(page.index)
+                        }
                     }
                 }
             }
-            Image(
-                painter = painter,
-                contentDescription = null,
-                modifier = contentModifier.fillMaxSize(),
-                contentScale = contentScale,
-                colorFilter = when {
-                    grayScale && invert -> grayScaleAndInvertFilter
-                    grayScale -> grayScaleFilter
-                    invert -> invertFilter
-                    else -> null
-                },
-            )
+            painter?.let { painter ->
+                val grayScale by Settings.grayScale.collectAsState()
+                val invert by Settings.invertedColors.collectAsState()
+                Image(
+                    painter = painter,
+                    contentDescription = null,
+                    modifier = contentModifier.fillMaxSize(),
+                    contentScale = contentScale,
+                    colorFilter = when {
+                        grayScale && invert -> grayScaleAndInvertFilter
+                        grayScale -> grayScaleFilter
+                        invert -> invertFilter
+                        else -> null
+                    },
+                )
+            }
         }
         is PageStatus.Blocked -> {
             AdsPlaceholder(