fix issue #724 & #711 - two threads attempt to use the same database connection & prepared statements

Tests/FMDatabaseQueueTests.m

@@ -369,4 +369,24 @@ - (void)testClose
     }];
 }
 
+- (void)testResultSetDealloc
+{
+    [self.queue inDatabase:^(FMDatabase * _Nonnull db) {
+        [db executeUpdate:@"create table if not exists test (a text, b text, c text, d text)"];
+        for (int i = 0; i < 10; i++) {
+            [db executeUpdate:@"insert into test (a, b, c, d) values ('1', '1', '1','1')"];
+        }
+    }];
+
+    size_t ops = 10;
+
+    dispatch_queue_t dqueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
+
+    dispatch_apply(ops, dqueue, ^(size_t nby) {
+        [self.queue inDatabase:^(FMDatabase *db) {
+            [db executeQuery:@"select * from test"];
+        }];
+    });
+}
+
 @end

src/fmdb/FMDatabaseQueue.m

@@ -195,6 +195,7 @@ - (void)inDatabase:(__attribute__((noescape)) void (^)(FMDatabase *db))block {
 
         if ([db hasOpenResultSets]) {
             NSLog(@"Warning: there is at least one open result set around after performing [FMDatabaseQueue inDatabase:]");
+            [db closeOpenResultSets];
 
 #if defined(DEBUG) && DEBUG
             NSSet *openSetCopy = FMDBReturnAutoreleased([[db valueForKey:@"_openResultSets"] copy]);