Add META-INF/services metadata to support Kotlin coroutines Dispatchers.Main.

Author: EdgarTwigg

CHANGES.md

@@ -1,6 +1,8 @@
 # DurianSwt releases
 
 ## [Unreleased]
+### Added
+- Add `META-INF/services` metadata to support Kotlin coroutines `Dispatchers.Main`.
 
 ## [5.0.1] - 2025-01-26
 ### Changed

durian-swt/src/main/java/com/diffplug/durian/swt/coroutines/SwtMainDispatcherFactory.kt

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2020-2025 DiffPlug
+ *
+ * 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
+ *
+ *     https://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 com.diffplug.durian.swt.coroutines
+
+import com.diffplug.common.swt.SwtExec
+import kotlinx.coroutines.InternalCoroutinesApi
+import kotlinx.coroutines.MainCoroutineDispatcher
+import kotlinx.coroutines.internal.MainDispatcherFactory
+import org.eclipse.swt.widgets.Display
+
+/**
+ * Factory for creating SWT-based main coroutine dispatcher.
+ * 
+ * This factory integrates SWT's UI thread with Kotlin coroutines by providing
+ * the SWT Display thread as the main dispatcher. When this library is on the 
+ * classpath, coroutines launched on Dispatchers.Main will automatically execute
+ * on the SWT UI thread.
+ * 
+ * The factory uses [SwtExec.immediate] which provides optimal performance:
+ * - Executes immediately when already on the SWT thread
+ * - Uses Display.asyncExec for cross-thread dispatch
+ * 
+ * @see SwtExec.immediate
+ */
+@OptIn(InternalCoroutinesApi::class)
+class SwtMainDispatcherFactory : MainDispatcherFactory {
+    
+    /**
+     * Load order priority for this factory.
+     * Higher values have higher priority. Using a moderate value to allow
+     * other UI toolkit factories to potentially override if needed.
+     */
+    override val loadPriority: Int = 100
+    
+    /**
+     * Creates the main dispatcher if SWT Display is available.
+     * 
+     * @param allFactories All available main dispatcher factories (unused)
+     * @return SWT-based main dispatcher
+     * @throws IllegalStateException if SWT Display is not available
+     */
+    override fun createDispatcher(allFactories: List<MainDispatcherFactory>): MainCoroutineDispatcher {
+        try {
+            // Try to get the default Display - this will fail if SWT is not properly initialized
+            // or if we're in a headless environment
+            Display.getDefault()
+            
+            // If we got here successfully, SWT is available
+            // Return the dispatcher from SwtExec.immediate() which provides optimal thread handling
+            return SwtExec.immediate().rxExecutor.dispatcher as MainCoroutineDispatcher
+        } catch (e: Exception) {
+            // SWT Display is not available (headless environment, not initialized, etc.)
+            // Throw an exception as the interface no longer supports nullable returns
+            throw IllegalStateException("SWT Display is not available", e)
+        }
+    }
+    
+    /**
+     * Hint about the expected dispatcher type.
+     * Returns null since we throw an exception when SWT is not available.
+     */
+    override fun hintOnError(): String? = null
+}

durian-swt/src/main/resources/META-INF/services/kotlinx.coroutines.internal.MainDispatcherFactory

@@ -0,0 +1 @@
+com.diffplug.durian.swt.coroutines.SwtMainDispatcherFactory