+#include <assert.h>
+
+#ifdef HAVE_BACKTRACE
+#include <execinfo.h>
+#include <stdio.h>
+#include <stdlib.h>
+#endif
+
+static void xcb_xlib_printbt(void)
+{
+#ifdef HAVE_BACKTRACE
+ void *array[20];
+ int size;
+ char **strings;
+ int i;
+
+ size = backtrace(array, 20);
+ strings = backtrace_symbols(array, size);
+
+ fprintf(stderr, "Locking assertion failure. Backtrace:\n");
+
+ for (i = 0; i < size; ++i)
+ fprintf(stderr, "#%i %s\n", i, strings[i]);
+
+ free(strings);
+#endif
+}
+
+#ifndef NDEBUG
+#define xcb_assert(c,x) do { if (!(x)) { xcb_xlib_printbt(); if (!(c)->xlib.sloppy_lock) assert(x); } } while(0)
+#else
+#define xcb_assert(c,x)
+#endif
+
+unsigned int xcb_get_request_sent(xcb_connection_t *c)
+{
+ if(c->has_error)
+ return 0;
+ return c->out.request;
+}
+
+void xcb_xlib_lock(xcb_connection_t *c)