Add stats counters for number of zero reallocs

test/unit/zero_reallocs.c

@@ -0,0 +1,40 @@
+#include "test/jemalloc_test.h"
+
+static size_t
+zero_reallocs() {
+	if (!config_stats) {
+		return 0;
+	}
+	size_t count = 12345;
+	size_t sz = sizeof(count);
+
+	assert_d_eq(mallctl("stats.zero_reallocs", (void *)&count, &sz,
+	    NULL, 0), 0, "Unexpected mallctl failure");
+	return count;
+}
+
+TEST_BEGIN(test_zero_reallocs) {
+	test_skip_if(!config_stats);
+
+	for (size_t i = 0; i < 100; ++i) {
+		void *ptr = mallocx(i * i + 1, 0);
+		assert_ptr_not_null(ptr, "Unexpected mallocx error");
+		size_t count = zero_reallocs();
+		assert_zu_eq(i, count, "Incorrect zero realloc count");
+		ptr = realloc(ptr, 0);
+		assert_ptr_null(ptr, "Realloc didn't free");
+		count = zero_reallocs();
+		assert_zu_eq(i + 1, count, "Realloc didn't adjust count");
+	}
+}
+TEST_END
+
+int
+main(void) {
+	/*
+	 * We expect explicit counts; reentrant tests run multiple times, so
+	 * counts leak across runs.
+	 */
+	return test_no_reentrancy(
+	    test_zero_reallocs);
+}

test/unit/zero_reallocs.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+export MALLOC_CONF="zero_realloc:free"