From 785903ae6d157ebda824e4e841f1f63aa93f9208 Mon Sep 17 00:00:00 2001
From: Maas-Maarten Zeeman <mmzeeman@xs4all.nl>
Date: Wed, 22 Feb 2017 22:03:26 +0100
Subject: [PATCH] Keep a reference to the connection before the prepare
 statement is put on the command queue.

This should fix a race condition when a prepare is called right before the
db connection is garbage collected.
---
 c_src/esqlite3_nif.c | 15 ++++++++++-----
 src/esqlite3.erl     |  4 ++--
 src/esqlite3_nif.erl |  4 ++--
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/c_src/esqlite3_nif.c b/c_src/esqlite3_nif.c
index 3b46fdb..f836cef 100644
--- a/c_src/esqlite3_nif.c
+++ b/c_src/esqlite3_nif.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2011, 2012, 2013 Maas-Maarten Zeeman
+ * Copyright 2011 - 2017 Maas-Maarten Zeeman
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -346,12 +346,12 @@ do_prepare(ErlNifEnv *env, esqlite_connection *conn, const ERL_NIF_TERM arg)
 	    return make_error_tuple(env, "no_memory");
 
     rc = sqlite3_prepare_v2(conn->db, (char *) bin.data, bin.size, &(stmt->statement), &tail);
-    if(rc != SQLITE_OK)
-	    return make_sqlite3_error_tuple(env, rc, conn->db);
+    if(rc != SQLITE_OK) {
+        enif_release_resource(conn);
+        return make_sqlite3_error_tuple(env, rc, conn->db);
+    }
 
-    enif_keep_resource(conn);
     stmt->connection = conn;
-
     esqlite_stmt = enif_make_resource(env, stmt);
     enif_release_resource(stmt);
 
@@ -871,6 +871,11 @@ esqlite_prepare(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
     if(!cmd) 
 	    return make_error_tuple(env, "command_create_failed");
 
+    /* Keep a reference to the connection to prevent it from being taken down
+     * while the prepare statement is waiting on the queue.
+     */
+    enif_keep_resource(conn);
+
     cmd->type = cmd_prepare;
     cmd->ref = enif_make_copy(cmd->env, argv[1]);
     cmd->pid = pid;
diff --git a/src/esqlite3.erl b/src/esqlite3.erl
index caffdd0..3f5b1b2 100644
--- a/src/esqlite3.erl
+++ b/src/esqlite3.erl
@@ -1,9 +1,9 @@
 %% @author Maas-Maarten Zeeman <mmzeeman@xs4all.nl>
-%% @copyright 2011, 2012, 2013 Maas-Maarten Zeeman
+%% @copyright 2011 - 2017 Maas-Maarten Zeeman
 
 %% @doc Erlang API for sqlite3 databases
 
-%% Copyright 2011, 2012 Maas-Maarten Zeeman
+%% Copyright 2011 - 2017 Maas-Maarten Zeeman
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
diff --git a/src/esqlite3_nif.erl b/src/esqlite3_nif.erl
index ca1bad5..1cbd0b6 100644
--- a/src/esqlite3_nif.erl
+++ b/src/esqlite3_nif.erl
@@ -1,9 +1,9 @@
 %% @author Maas-Maarten Zeeman <mmzeeman@xs4all.nl>
-%% @copyright 2011, 2012, 2013 Maas-Maarten Zeeman
+%% @copyright 2011 - 2017 Maas-Maarten Zeeman
 
 %% @doc Low level erlang API for sqlite3 databases
 
-%% Copyright 2011, 2012, 2013, 2014 Maas-Maarten Zeeman
+%% Copyright 2011 - 2017 Maas-Maarten Zeeman
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.