Optimize the statement check for a non-discarded database

This also restores the ability (now tested!) to call Database#close
successfully and defer its cleanup until after Statements are closed,
which was the promise of #557 and sqlite3_close_v2.

Closes #564

ext/sqlite3/database.c

@@ -49,15 +49,16 @@ discard_db(sqlite3RubyPtr ctx)
     }
 
     ctx->db = NULL;
+    ctx->flags |= SQLITE3_RB_DATABASE_DISCARDED;
 }
 
 static void
 close_or_discard_db(sqlite3RubyPtr ctx)
 {
     if (ctx->db) {
-        int isReadonly = (ctx->flags & SQLITE_OPEN_READONLY);
+        int is_readonly = (ctx->flags & SQLITE3_RB_DATABASE_READONLY);
 
-        if (isReadonly || ctx->owner == getpid()) {
+        if (is_readonly || ctx->owner == getpid()) {
             // Ordinary close.
             sqlite3_close_v2(ctx->db);
             ctx->db = NULL;
@@ -153,7 +154,9 @@ rb_sqlite3_open_v2(VALUE self, VALUE file, VALUE mode, VALUE zvfs)
              );
 
     CHECK(ctx->db, status);
-    ctx->flags = flags;
+    if (flags & SQLITE_OPEN_READONLY) {
+        ctx->flags |= SQLITE3_RB_DATABASE_READONLY;
+    }
 
     return self;
 }
@@ -943,11 +946,10 @@ rb_sqlite3_open16(VALUE self, VALUE file)
 #endif
 #endif
 
-    status = sqlite3_open16(utf16_string_value_ptr(file), &ctx->db);
-
-    // these are the perm flags used implicitly by sqlite3_open16,
+    // sqlite3_open16 implicitly uses flags (SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE)
     // see https://www.sqlite.org/capi3ref.html#sqlite3_open
-    ctx->flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
+    // so we do not ever set SQLITE3_RB_DATABASE_READONLY in ctx->flags
+    status = sqlite3_open16(utf16_string_value_ptr(file), &ctx->db);
 
     CHECK(ctx->db, status)
 

ext/sqlite3/database.h

@@ -3,6 +3,10 @@
 
 #include <sqlite3_ruby.h>
 
+/* bits in the `flags` field */
+#define SQLITE3_RB_DATABASE_READONLY  0x01
+#define SQLITE3_RB_DATABASE_DISCARDED 0x02
+
 struct _sqlite3Ruby {
     sqlite3 *db;
     VALUE busy_handler;

ext/sqlite3/statement.c

@@ -1,22 +1,12 @@
 #include <sqlite3_ruby.h>
 
 #define REQUIRE_OPEN_STMT(_ctxt) \
-  if(!_ctxt->st) \
+  if (!_ctxt->st) \
     rb_raise(rb_path2class("SQLite3::Exception"), "cannot use a closed statement");
 
-static void
-require_open_db(VALUE stmt_rb)
-{
-    VALUE closed_p = rb_funcall(
-                         rb_iv_get(stmt_rb, "@connection"),
-                         rb_intern("closed?"), 0);
-
-    if (RTEST(closed_p)) {
-        rb_raise(rb_path2class("SQLite3::Exception"),
-                 "cannot use a statement associated with a closed database");
-    }
-}
-
+#define REQUIRE_LIVE_DB(_ctxt) \
+  if (_ctxt->db->flags & SQLITE3_RB_DATABASE_DISCARDED) \
+    rb_raise(rb_path2class("SQLite3::Exception"), "cannot use a statement associated with a discarded database");
 
 VALUE cSqlite3Statement;
 
@@ -71,6 +61,11 @@ prepare(VALUE self, VALUE db, VALUE sql)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
+    /* Dereferencing a pointer to the database struct will be faster than accessing it through the
+     * instance variable @connection. The struct pointer is guaranteed to be live because instance
+     * variable will keep it from being GCed. */
+    ctx->db = db_ctx;
+
 #ifdef HAVE_SQLITE3_PREPARE_V2
     status = sqlite3_prepare_v2(
 #else
@@ -135,7 +130,7 @@ step(VALUE self)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     if (ctx->done_p) { return Qnil; }
@@ -232,7 +227,7 @@ bind_param(VALUE self, VALUE key, VALUE value)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     switch (TYPE(key)) {
@@ -326,7 +321,7 @@ reset_bang(VALUE self)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     sqlite3_reset(ctx->st);
@@ -348,7 +343,7 @@ clear_bindings_bang(VALUE self)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     sqlite3_clear_bindings(ctx->st);
@@ -382,7 +377,7 @@ column_count(VALUE self)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     return INT2NUM(sqlite3_column_count(ctx->st));
@@ -415,7 +410,7 @@ column_name(VALUE self, VALUE index)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     name = sqlite3_column_name(ctx->st, (int)NUM2INT(index));
@@ -440,7 +435,7 @@ column_decltype(VALUE self, VALUE index)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     name = sqlite3_column_decltype(ctx->st, (int)NUM2INT(index));
@@ -459,7 +454,7 @@ bind_parameter_count(VALUE self)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     return INT2NUM(sqlite3_bind_parameter_count(ctx->st));
@@ -568,7 +563,7 @@ stats_as_hash(VALUE self)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     VALUE arg = rb_hash_new();
@@ -587,7 +582,7 @@ stat_for(VALUE self, VALUE key)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     if (SYMBOL_P(key)) {
@@ -609,7 +604,7 @@ memused(VALUE self)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     return INT2NUM(sqlite3_stmt_status(ctx->st, SQLITE_STMTSTATUS_MEMUSED, 0));
@@ -628,7 +623,7 @@ database_name(VALUE self, VALUE index)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     return SQLITE3_UTF8_STR_NEW2(
@@ -647,7 +642,7 @@ get_sql(VALUE self)
     sqlite3StmtRubyPtr ctx;
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     return rb_obj_freeze(SQLITE3_UTF8_STR_NEW2(sqlite3_sql(ctx->st)));
@@ -667,7 +662,7 @@ get_expanded_sql(VALUE self)
 
     TypedData_Get_Struct(self, sqlite3StmtRuby, &statement_type, ctx);
 
-    require_open_db(self);
+    REQUIRE_LIVE_DB(ctx);
     REQUIRE_OPEN_STMT(ctx);
 
     expanded_sql = sqlite3_expanded_sql(ctx->st);

ext/sqlite3/statement.h

@@ -5,6 +5,7 @@
 
 struct _sqlite3StmtRuby {
     sqlite3_stmt *st;
+    sqlite3Ruby *db;
     int done_p;
 };
 

test/test_discarding.rb

@@ -160,7 +160,7 @@ def test_a_discarded_connection_with_statements
         db.send(:discard)
 
         e = assert_raises(SQLite3::Exception) { stmt.execute }
-        assert_match(/cannot use a statement associated with a closed database/, e.message)
+        assert_match(/cannot use a statement associated with a discarded database/, e.message)
 
         assert_nothing_raised { stmt.close }
         assert_predicate(stmt, :closed?)

test/test_statement.rb

@@ -135,6 +135,13 @@ def test_new_closed_handle
       end
     end
 
+    def test_closed_db_behavior
+      @db.close
+      result = nil
+      assert_nothing_raised { result = @stmt.execute }
+      refute_nil result
+    end
+
     def test_new_with_remainder
       stmt = SQLite3::Statement.new(@db, "select 'foo';bar")
       assert_equal "bar", stmt.remainder