Fix support for async API on WebGL platforms

Author: gilzoide

Plugins/tools~/fix-library-path.sed

@@ -34,3 +34,6 @@ s/class SQLite3/partial class SQLite3/
 # Add [RequiredMember] attribute to ColumnInfo.Name property
 # This fixes managed code stripping removing its setter method
 s/Column ("name")/Column ("name"), UnityEngine.Scripting.RequiredMember/
+
+# Use main thread TaskScheduler in WebGL
+s/TaskScheduler\.Default/SQLiteAsyncExtensions.TaskScheduler/

README.md

@@ -114,3 +114,4 @@ Third-party code:
   This is be useful for libraries making raw queries.
 - `SQLite3.SetDirectory` is only defined in Windows platforms.
 - Adds a `[RequiredMember]` attribute to `ColumnInfo.Name` property, fixing errors on columns when managed code stripping is enabled.
+- Changes the `TaskScheduler` used by the async API on WebGL to one that executes tasks on Unity's main thread.

Runtime/SQLiteAsyncExtensions.cs

@@ -0,0 +1,23 @@
+using System.Threading.Tasks;
+using UnityEngine;
+
+namespace SQLite
+{
+    public static class SQLiteAsyncExtensions
+    {
+#if UNITY_WEBGL
+        // WebGL builds cannot use background threads, so use a
+        // TaskScheduler that executes tasks on Unity's main thread.
+        public static TaskScheduler TaskScheduler { get; private set; }
+
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]
+        private static void InitializeTaskScheduler()
+        {
+            TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext();
+        }
+#else
+        // On all other platforms, use the default TaskScheduler
+        public static TaskScheduler TaskScheduler => TaskScheduler.Default;
+#endif
+    }
+}

Runtime/SQLiteAsyncExtensions.cs.meta

@@ -215,7 +215,7 @@ public Task CloseAsync ()
 		{
 			return Task.Factory.StartNew (() => {
 				SQLiteConnectionPool.Shared.CloseConnection (_connectionString);
-			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, SQLiteAsyncExtensions.TaskScheduler);
 		}
 
 		Task<T> ReadAsync<T> (Func<SQLiteConnectionWithLock, T> read)
@@ -225,7 +225,7 @@ Task<T> ReadAsync<T> (Func<SQLiteConnectionWithLock, T> read)
 				using (conn.Lock ()) {
 					return read (conn);
 				}
-			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, SQLiteAsyncExtensions.TaskScheduler);
 		}
 
 		Task<T> WriteAsync<T> (Func<SQLiteConnectionWithLock, T> write)
@@ -235,7 +235,7 @@ Task<T> WriteAsync<T> (Func<SQLiteConnectionWithLock, T> write)
 				using (conn.Lock ()) {
 					return write (conn);
 				}
-			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, SQLiteAsyncExtensions.TaskScheduler);
 		}
 
 		Task<T> TransactAsync<T> (Func<SQLiteConnectionWithLock, T> transact)
@@ -247,7 +247,7 @@ Task<T> TransactAsync<T> (Func<SQLiteConnectionWithLock, T> transact)
 						return transact (conn);
 					}
 				}
-			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, SQLiteAsyncExtensions.TaskScheduler);
 		}
 
 		/// <summary>
@@ -1201,7 +1201,7 @@ Task<U> ReadAsync<U> (Func<SQLiteConnectionWithLock, U> read)
 				using (conn.Lock ()) {
 					return read (conn);
 				}
-			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, SQLiteAsyncExtensions.TaskScheduler);
 		}
 
 		Task<U> WriteAsync<U> (Func<SQLiteConnectionWithLock, U> write)
@@ -1211,7 +1211,7 @@ Task<U> WriteAsync<U> (Func<SQLiteConnectionWithLock, U> write)
 				using (conn.Lock ()) {
 					return write (conn);
 				}
-			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+			}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, SQLiteAsyncExtensions.TaskScheduler);
 		}
 
 		/// <summary>