Switch to rb_ary_new2 and rb_ary_push to prevent GC segfault on params

to user-defined function. The new test_function_gc_segfault is skipped
because you don't want to see segfault when running rake test. Unskip the
test and comment out rb_ary_push to see the test fail.

Author: Jim Flood

ext/sqlite3/database.c

@@ -359,17 +359,22 @@ static void set_sqlite3_func_result(sqlite3_context * ctx, VALUE result)
 static void rb_sqlite3_func(sqlite3_context * ctx, int argc, sqlite3_value **argv)
 {
   VALUE callable = (VALUE)sqlite3_user_data(ctx);
-  VALUE params[argc]; /* RB_GC_GUARD unreliable -- keep values safely on the stack */
+  VALUE * params = NULL;
+  VALUE guard = rb_ary_new2(argc); /* Prevent garbage collection of params during call. */
   VALUE result;
   int i;
 
   if (argc > 0) {
+    params = xcalloc((size_t)argc, sizeof(VALUE *));
     for(i = 0; i < argc; i++) {
-      params[i] = sqlite3val2rb(argv[i]);
+      VALUE param = sqlite3val2rb(argv[i]);
+      rb_ary_push(guard, param);
+      params[i] = param;
     }
   }
 
   result = rb_funcall2(callable, rb_intern("call"), argc, params);
+  xfree(params);
 
   set_sqlite3_func_result(ctx, result);
 }

test/test_database.rb

@@ -279,6 +279,15 @@ def test_function_return_types
       end
     end
 
+    def test_function_gc_segfault
+      skip("Segfault is unsettling to see when running rake test")
+      @db.create_function("bug", -1) { |func, *values| func.result = values.join }
+      # With a lot of data and a lot of threads, try to induce a GC segfault.
+      params = Array.new(127, "?" * 28000)
+      proc = Proc.new { db.execute("select bug(#{Array.new(params.length, "?").join(",")})", *params) }
+      Mutex.new.tap { |m| threads = (0..30).inject([]) { |a| a << Thread.new { m.synchronize { proc.call } } }.each { |thread| thread.join } }
+    end
+
     def test_function_return_type_round_trip
       [10, 2.2, nil, "foo", Blob.new("foo\0bar")].each do |thing|
         @db.define_function("hello") { |a| a }