[Android] Create a LifecycleAwareScheduler class to replace the Handlers

[Nicolas Pomepuy]

vlc-android | branch: master | Nicolas Pomepuy <nicolas at videolabs.io> | Thu Jul 20 09:16:39 2023 +0200| [0cb23cbf90a8a76eaf070abc73aa7e62cf5fd744] | committer: Duncan McNamara

Create a LifecycleAwareScheduler class to replace the Handlers

> https://code.videolan.org/videolan/vlc-android/commit/0cb23cbf90a8a76eaf070abc73aa7e62cf5fd744
---

 .../videolan/vlc/util/LifecycleAwareScheduler.kt   | 142 +++++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/application/vlc-android/src/org/videolan/vlc/util/LifecycleAwareScheduler.kt b/application/vlc-android/src/org/videolan/vlc/util/LifecycleAwareScheduler.kt
new file mode 100644
index 0000000000..c0dd3d2b0f
--- /dev/null
+++ b/application/vlc-android/src/org/videolan/vlc/util/LifecycleAwareScheduler.kt
@@ -0,0 +1,142 @@
+/*
+ * ************************************************************************
+ *  LifecycleAwareScheduler.kt
+ * *************************************************************************
+ * Copyright © 2023 VLC authors and VideoLAN
+ * Author: Nicolas POMEPUY
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ * **************************************************************************
+ *
+ *
+ */
+
+package org.videolan.vlc.util
+
+import android.util.Log
+import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.lifecycleScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import org.videolan.vlc.BuildConfig
+import java.util.Timer
+import java.util.TimerTask
+import kotlin.concurrent.timerTask
+
+/**
+ * Callback for [LifecycleAwareScheduler].
+ * It will be used to listen to action trigger and cancellation
+ */
+interface SchedulerCallback : LifecycleOwner {
+    /**
+     * Called when the action should be performed.
+     * It's guaranteed to be ran on the main thread
+     *
+     * @param id the action id
+     */
+    fun onTaskTriggered(id: String)
+
+    /**
+     * (Optional) Called when the action is cancelled
+     *
+     * @param id the action id
+     */
+    fun onTaskCanceled(id: String) {}
+}
+
+/**
+ * Thread safe and lifecycle aware scheduler class.
+ * Its goal is to schedule tasks no matter what the thread it's launched in,
+ * cancel these tasks when the calling component is paused / destroyed
+ * and manage a task list
+ * This is a safer and easier to use replacement for Handler
+ *
+ * @property callback the listening [LifecycleOwner] to launch it
+ */
+class LifecycleAwareScheduler(private val callback: SchedulerCallback) : DefaultLifecycleObserver {
+
+    private val timer = Timer()
+    private val timeTasks = HashMap<String, TimerTask>()
+
+    init {
+        if (BuildConfig.DEBUG) Log.d("LifecycleAwareScheduler", "Creating LifecycleAwareScheduler for $callback")
+    }
+
+    /**
+     * Start an immediate action.
+     * Can be called in any thread
+     *
+     * @param id the action id
+     */
+    fun startAction(id: String) {
+        scheduleAction(id, 0L)
+    }
+
+    /**
+     * Schedule an action to be called in [delay]ms.
+     * Can be called in any thread
+     *
+     * @param id the action id
+     * @param delay the delay before the action is ran
+     */
+    fun scheduleAction(id: String, delay: Long) {
+        if (BuildConfig.DEBUG) Log.d("LifecycleAwareScheduler", "Scheduling action for $callback on thread ${Thread.currentThread()} with id $id")
+        callback.lifecycle.addObserver(this at LifecycleAwareScheduler)
+        if (timeTasks.keys.contains(id)) cancelAction(id)
+        timeTasks[id] = timerTask {
+            callback.lifecycleScope.launch(Dispatchers.Main) { callback.onTaskTriggered(id) }
+        }
+        timer.schedule(timeTasks[id], delay)
+    }
+
+    /**
+     * Cancel an existing action
+     *
+     * @param id the action id
+     * @return true if an action has been canceled, false otherwise
+     */
+    fun cancelAction(id: String): Boolean {
+        if (BuildConfig.DEBUG) Log.d("LifecycleAwareScheduler", "Canceling action for $callback on thread ${Thread.currentThread()} with id $id")
+        if (timeTasks.keys.contains(id)) {
+            timeTasks[id]?.cancel()
+            callback.onTaskCanceled(id)
+            timeTasks.remove(id)
+            return true
+        }
+        return false
+    }
+
+    /**
+     * Cancel the timer and off-hook from lifecycle callbacks
+     */
+    private fun discardTimer() {
+        timeTasks.forEach { callback.onTaskCanceled(it.key) }
+        timer.cancel()
+        callback.lifecycle.removeObserver(this)
+    }
+
+    override fun onPause(owner: LifecycleOwner) {
+        super.onPause(owner)
+        timeTasks.forEach {
+            it.value.cancel()
+            callback.onTaskCanceled(it.key)
+        }
+    }
+
+    override fun onDestroy(owner: LifecycleOwner) {
+        super.onDestroy(owner)
+        discardTimer()
+    }
+}
\ No newline at end of file