added new event dispatcher

src/dorkbox/network/connection/EventDispatcher.kt

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2023 dorkbox, llc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package dorkbox.network.connection
+
+import dorkbox.network.Configuration
+import dorkbox.util.NamedThreadFactory
+import kotlinx.atomicfu.atomic
+import kotlinx.coroutines.CoroutineName
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.asCoroutineDispatcher
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.launch
+import java.util.concurrent.*
+
+class EventDispatcher {
+    companion object {
+        // It CANNOT be the default dispatch because there will be thread starvation
+        // NOTE: THIS CANNOT CHANGE!! IT WILL BREAK EVERYTHING
+        private val defaultEventDispatcher = Executors.newSingleThreadExecutor(
+            NamedThreadFactory("Event Dispatcher", Configuration.networkThreadGroup, Thread.NORM_PRIORITY, true)
+        )
+
+        private val asDispatcher = defaultEventDispatcher.asCoroutineDispatcher()
+
+        private val instances = atomic(0)
+    }
+
+    @Volatile
+    private var dispatchThreadId = 0L
+
+    @Volatile
+    private var forceLaunch = false
+
+
+    val wasForced: Boolean
+        get() = forceLaunch
+
+
+    private val eventDispatch = CoroutineScope(asDispatcher + CoroutineName("asdfasdfasdfasdf"))
+
+    val isActive: Boolean
+        get() = eventDispatch.isActive
+
+    val isCurrent: Boolean
+        get() = dispatchThreadId == Thread.currentThread().id
+
+    init {
+        instances.getAndIncrement()
+        eventDispatch.launch {
+            dispatchThreadId = Thread.currentThread().id
+        }
+    }
+
+
+    /**
+     * When this method is called, it can be called from different 'threads'
+     *  - from a different thread
+     *  - from a different coroutine
+     *  - from the "same" coroutine
+     *
+     *  When it is from the same coroutine or from *something* whose thread originated from us, we DO NOT want to re-dispatch the event,
+     *  we want to immediately execute it (via runBlocking)
+     */
+    fun launch(function: suspend () -> Unit): Job {
+        return if (dispatchThreadId == Thread.currentThread().id) {
+            kotlinx.coroutines.runBlocking {
+                function()
+            }
+            // this job cannot be cancelled, because it will have already run by now
+            Job()
+        } else {
+            eventDispatch.launch {
+                function()
+            }
+        }
+    }
+
+    /**
+     * Force launching the function on the event dispatch. This is for the RARE occasion that we want to make sure (that when running inside
+     * our current dispatch) to FINISH running the current logic before executing the NEW logic...
+     */
+    fun forceLaunch(function: suspend () -> Unit): Job {
+        forceLaunch = true
+        return eventDispatch.launch {
+            function()
+            forceLaunch = false
+        }
+    }
+
+    fun cancel(cause: String) {
+        // because we have a SHARED thread executor-as-a-coroutine-dispatcher, if we CANCEL on one instance, it will cancel ALL instances.
+        val count = instances.decrementAndGet()
+        if (count == 0) {
+            eventDispatch.cancel(cause)
+        }
+    }
+
+    fun runBlocking(function: suspend () -> Unit) {
+        kotlinx.coroutines.runBlocking {
+            function()
+        }
+    }
+}