Simplify PageHolder load Job (#9086)

Inline statusJob into loadJob, using supervisorScope to load the page
and track status changes in parallel.
- supervisorScope does not complete until both the child loadPage
  coroutine and statusFlow.collectLatest have completed.
- Cancelling supervisorScope cancels the child loadPage coroutine and
  statusFlow.collectLatest.
- Use supervisorScope instead of coroutineScope to let status
  collection continue if loadPage fails.

Inline progressJob into loadJob, using collectLatest's cancellation
to avoid cancelling the progressFlow collection explicitly.
- collectLatest cancels the previous action block when the flow
  emits a new value. This means the DOWNLOAD_IMAGE
  progressFlow.collectLatest gets automatically cancelled when
  statusFlow emits a new state.

Convert launchLoadJob to suspend function, move job launch to caller,
and rename as loadPageAndProcessStatus.

(cherry picked from commit 4635e58405eedce0b49fc69f7ccb190a7c600da9)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerPageHolder.kt

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerPageHolder.kt

@@ -20,18 +20,19 @@ import kotlinx.coroutines.MainScope
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.supervisorScope
 import logcat.LogPriority
 import rx.Observable
 import rx.Subscription
 import rx.android.schedulers.AndroidSchedulers
 import rx.schedulers.Schedulers
+import tachiyomi.core.util.lang.launchIO
 import tachiyomi.core.util.system.logcat
 import tachiyomi.decoder.ImageDecoder
 import java.io.BufferedInputStream
 import java.io.ByteArrayInputStream
 import java.io.InputStream
 import kotlin.math.max
-import kotlin.math.roundToInt
 
 /**
  * View of the ViewPager that contains a page of a chapter.
@@ -67,35 +68,15 @@ class PagerPageHolder(
     private val scope = MainScope()
 
     /**
-     * Job for loading the page.
+     * Job for loading the page and processing changes to the page's status.
      */
     private var loadJob: Job? = null
 
-    /**
-     * Job for status changes of the page.
-     */
-    private var statusJob: Job? = null
-
-    /**
-     * Job for progress changes of the page.
-     */
-    private var progressJob: Job? = null
-
     /**
      * Job for loading the page.
      */
     private var extraLoadJob: Job? = null
 
-    /**
-     * Job for status changes of the page.
-     */
-    private var extraStatusJob: Job? = null
-
-    /**
-     * Job for progress changes of the page.
-     */
-    private var extraProgressJob: Job? = null
-
     /**
      * Subscription used to read the header of the image. This is needed in order to instantiate
      * the appropiate image view depending if the image is animated (GIF).
@@ -104,7 +85,8 @@ class PagerPageHolder(
 
     init {
         addView(progressIndicator)
-        launchLoadJob()
+        loadJob = scope.launch { loadPageAndProcessStatus(1) }
+        extraLoadJob = scope.launch { loadPageAndProcessStatus(2) }
     }
 
     /**
@@ -113,132 +95,47 @@ class PagerPageHolder(
     @SuppressLint("ClickableViewAccessibility")
     override fun onDetachedFromWindow() {
         super.onDetachedFromWindow()
-        cancelProgressJob(1)
+        loadJob?.cancel()
-        cancelProgressJob(2)
+        loadJob = null
-        cancelLoadJob(1)
+        extraLoadJob?.cancel()
-        cancelLoadJob(2)
+        extraLoadJob = null
         unsubscribeReadImageHeader()
     }
 
     /**
-     * Starts loading the page and processing changes to the page's status.
+     * Loads the page and processes changes to the page's status.
      *
-     * @see processStatus
+     * Returns immediately if the page has no PageLoader.
+     * Otherwise, this function does not return. It will continue to process status changes until
+     * the Job is cancelled.
      */
-    private fun launchLoadJob() {
+    private suspend fun loadPageAndProcessStatus(pageIndex: Int) {
-        loadJob?.cancel()
-        statusJob?.cancel()
-
-        val loader = page.chapter.pageLoader ?: return
-        loadJob = scope.launch {
-            loader.loadPage(page)
-        }
-        statusJob = scope.launch {
-            page.statusFlow.collectLatest { processStatus(it) }
-        }
-
         // SY -->
-        val extraPage = extraPage ?: return
+        val page = if (pageIndex == 1) page else extraPage
-        val loader2 = extraPage.chapter.pageLoader ?: return
+        page ?: return
-        extraLoadJob = scope.launch {
-            loader2.loadPage(extraPage)
-        }
-        extraStatusJob = scope.launch {
-            extraPage.statusFlow.collectLatest { processStatus2(it) }
-        }
         // SY <--
-    }
+        val loader = page.chapter.pageLoader ?: return
-
+        supervisorScope {
-    private fun launchProgressJob() {
+            launchIO {
-        progressJob?.cancel()
+                loader.loadPage(page)
-        progressJob = scope.launch {
-            page.progressFlow.collectLatest { value -> progressIndicator.setProgress(value) }
-        }
-    }
-
-    private fun launchProgressJob2() {
-        extraProgressJob?.cancel()
-        val extraPage = extraPage ?: return
-        extraProgressJob = scope.launch {
-            extraPage.progressFlow.collectLatest { value -> progressIndicator.setProgress(((page.progressFlow.value + value) / 2 * 0.95f).roundToInt()) }
-        }
-    }
-
-    /**
-     * Called when the status of the page changes.
-     *
-     * @param status the new status of the page.
-     */
-    private fun processStatus(status: Page.State) {
-        when (status) {
-            Page.State.QUEUE -> setQueued()
-            Page.State.LOAD_PAGE -> setLoading()
-            Page.State.DOWNLOAD_IMAGE -> {
-                launchProgressJob()
-                setDownloading()
             }
-            Page.State.READY -> {
+            page.statusFlow.collectLatest { state ->
-                if (extraPage?.status == Page.State.READY || extraPage == null) {
+                when (state) {
-                    setImage()
+                    Page.State.QUEUE -> setQueued()
+                    Page.State.LOAD_PAGE -> setLoading()
+                    Page.State.DOWNLOAD_IMAGE -> {
+                        setDownloading()
+                        page.progressFlow.collectLatest { value ->
+                            progressIndicator.setProgress(value)
+                        }
+                    }
+                    Page.State.READY -> setImage()
+                    Page.State.ERROR -> setError()
                 }
-                cancelProgressJob(1)
-            }
-            Page.State.ERROR -> {
-                setError()
-                cancelProgressJob(1)
             }
         }
     }
 
-    /**
-     * Called when the status of the page changes.
-     *
-     * @param status the new status of the page.
-     */
-    private fun processStatus2(status: Page.State) {
-        when (status) {
-            Page.State.QUEUE -> setQueued()
-            Page.State.LOAD_PAGE -> setLoading()
-            Page.State.DOWNLOAD_IMAGE -> {
-                launchProgressJob2()
-                setDownloading()
-            }
-            Page.State.READY -> {
-                if (page.status == Page.State.READY) {
-                    setImage()
-                }
-                cancelProgressJob(2)
-            }
-            Page.State.ERROR -> {
-                setError()
-                cancelProgressJob(2)
-            }
-        }
-    }
-
-    /**
-     * Cancels loading the page and processing changes to the page's status.
-     */
-    private fun cancelLoadJob(page: Int) {
-        if (page == 1) {
-            loadJob?.cancel()
-            loadJob = null
-            statusJob?.cancel()
-            statusJob = null
-        } else if (page == 2) {
-            extraLoadJob?.cancel()
-            extraLoadJob = null
-            extraStatusJob?.cancel()
-            extraStatusJob = null
-        }
-    }
-
-    private fun cancelProgressJob(page: Int) {
-        val job = if (page == 1) progressJob else extraProgressJob
-        job?.cancel()
-        if (page == 1) progressJob = null else extraProgressJob = null
-    }
-
     /**
      * Unsubscribes from the read image header subscription.
      */

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/webtoon/WebtoonPageHolder.kt

@@ -24,10 +24,12 @@ import kotlinx.coroutines.Job
 import kotlinx.coroutines.MainScope
 import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.supervisorScope
 import rx.Observable
 import rx.Subscription
 import rx.android.schedulers.AndroidSchedulers
 import rx.schedulers.Schedulers
+import tachiyomi.core.util.lang.launchIO
 import java.io.BufferedInputStream
 import java.io.InputStream
 
@@ -77,16 +79,6 @@ class WebtoonPageHolder(
      */
     private var loadJob: Job? = null
 
-    /**
-     * Job for status changes of the page.
-     */
-    private var statusJob: Job? = null
-
-    /**
-     * Job for progress changes of the page.
-     */
-    private var progressJob: Job? = null
-
     /**
      * Subscription used to read the header of the image. This is needed in order to instantiate
      * the appropriate image view depending if the image is animated (GIF).
@@ -106,7 +98,8 @@ class WebtoonPageHolder(
      */
     fun bind(page: ReaderPage) {
         this.page = page
-        launchLoadJob()
+        loadJob?.cancel()
+        loadJob = scope.launch { loadPageAndProcessStatus() }
         refreshLayoutParams()
     }
 
@@ -126,8 +119,8 @@ class WebtoonPageHolder(
      * Called when the view is recycled and added to the view pool.
      */
     override fun recycle() {
-        cancelLoadJob()
+        loadJob?.cancel()
-        cancelProgressJob()
+        loadJob = null
         unsubscribeReadImageHeader()
 
         removeErrorLayout()
@@ -136,78 +129,36 @@ class WebtoonPageHolder(
     }
 
     /**
-     * Starts loading the page and processing changes to the page's status.
+     * Loads the page and processes changes to the page's status.
      *
-     * @see processStatus
+     * Returns immediately if there is no page or the page has no PageLoader.
+     * Otherwise, this function does not return. It will continue to process status changes until
+     * the Job is cancelled.
      */
-    private fun launchLoadJob() {
+    private suspend fun loadPageAndProcessStatus() {
-        cancelLoadJob()
-
         val page = page ?: return
         val loader = page.chapter.pageLoader ?: return
-        loadJob = scope.launch {
+        supervisorScope {
-            loader.loadPage(page)
+            launchIO {
-        }
+                loader.loadPage(page)
-        statusJob = scope.launch {
-            page.statusFlow.collectLatest { processStatus(it) }
-        }
-    }
-
-    /**
-     * Observes the progress of the page and updates view.
-     */
-    private fun launchProgressJob() {
-        cancelProgressJob()
-
-        val page = page ?: return
-
-        progressJob = scope.launch {
-            page.progressFlow.collectLatest { value -> progressIndicator.setProgress(value) }
-        }
-    }
-
-    /**
-     * Called when the status of the page changes.
-     *
-     * @param status the new status of the page.
-     */
-    private fun processStatus(status: Page.State) {
-        when (status) {
-            Page.State.QUEUE -> setQueued()
-            Page.State.LOAD_PAGE -> setLoading()
-            Page.State.DOWNLOAD_IMAGE -> {
-                launchProgressJob()
-                setDownloading()
             }
-            Page.State.READY -> {
+            page.statusFlow.collectLatest { state ->
-                setImage()
+                when (state) {
-                cancelProgressJob()
+                    Page.State.QUEUE -> setQueued()
-            }
+                    Page.State.LOAD_PAGE -> setLoading()
-            Page.State.ERROR -> {
+                    Page.State.DOWNLOAD_IMAGE -> {
-                setError()
+                        setDownloading()
-                cancelProgressJob()
+                        page.progressFlow.collectLatest { value ->
+                            progressIndicator.setProgress(value)
+                        }
+                    }
+                    Page.State.READY -> setImage()
+                    Page.State.ERROR -> setError()
+                }
             }
         }
     }
 
-    /**
-     * Cancels loading the page and processing changes to the page's status.
-     */
-    private fun cancelLoadJob() {
-        loadJob?.cancel()
-        loadJob = null
-        statusJob?.cancel()
-        statusJob = null
-    }
-
-    /**
-     * Unsubscribes from the progress subscription.
-     */
-    private fun cancelProgressJob() {
-        progressJob?.cancel()
-        progressJob = null
-    }
-
     /**
      * Unsubscribes from the read image header subscription.
      */