Merge pull request #744 from groue/dev/fix-741

Fix DatabaseMigrator deadlock with serial target queues
groue · Mar 29, 2020 · ba0c771 · ba0c771
2 parents e831c64 + 97a84c6
commit ba0c771
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diff --git a/GRDB/Migration/DatabaseMigrator.swift b/GRDB/Migration/DatabaseMigrator.swift
@@ -160,7 +160,9 @@ public struct DatabaseMigrator {
                         //
                         // Create a temporary witness database (on disk, just in case
                         // migrations would involve a lot of data).
-                        let witness = try DatabaseQueue(path: "", configuration: writer.configuration)
+                        var witnessConfiguration = writer.configuration
+                        witnessConfiguration.targetQueue = nil // Avoid deadlocks
+                        let witness = try DatabaseQueue(path: "", configuration: witnessConfiguration)
 
                         // Grab schema of migrated witness database
                         let witnessSchema: SchemaInfo = try witness.writeWithoutTransaction { db in

diff --git a/Tests/GRDBTests/DatabaseMigratorTests.swift b/Tests/GRDBTests/DatabaseMigratorTests.swift
@@ -553,6 +553,20 @@ class DatabaseMigratorTests : GRDBTestCase {
         try XCTAssertTrue(dbQueue.read(newMigrator.hasCompletedMigrations))
     }
 
+    // Regression test for https://github.com/groue/GRDB.swift/issues/741
+    func testEraseDatabaseOnSchemaChangeDoesNotDeadLock() throws {
+        dbConfiguration.targetQueue = DispatchQueue(label: "target")
+        let dbQueue = try makeDatabaseQueue()
+
+        var migrator = DatabaseMigrator()
+        migrator.eraseDatabaseOnSchemaChange = true
+        migrator.registerMigration("1", migrate: { _ in })
+        try migrator.migrate(dbQueue)
+
+        migrator.registerMigration("2", migrate: { _ in })
+        try migrator.migrate(dbQueue)
+    }
+
     func testEraseDatabaseOnSchemaChange() throws {
         // 1st version of the migrator
         var migrator1 = DatabaseMigrator()