Re: test-memmem takes waaay too long

[Eric Blake]

Ralf Wildenhues <Ralf.Wildenhues <at> gmx.de> writes:

> 
> I suggest that either the testsuite test use some time limit (alarm?),
> or the configure test tries to expose the quadratic complexity, or the
> configure test assume `no' on systems where we know libc's memmem to be
> insufficient.

I'm still planning on asking the Austin group whether strstr must be async-safe 
or must have linear complexity, or whether this tradeoff between the two 
competing ideals should be left as a QoI issue for various implementations.  
Once I get an answer for that, we can extrapolate the same answer for memmem.  
In the meantime, I'm checking this in; test-memmem now fails instead of passing 
on glibc systems, but at least the failure is after 10 seconds rather than 
taking many minutes before passing.

Since the cross-compilation test already pessimistically assumes memmem has bad 
complexity, it is not that hard to alter the runtime test in memmem.m4 to use 
the same approach as test-memmem.c to flush out glibc and other systems with 
poor complexity.  However, I'm reluctant to change the actual memmem.m4 test to 
try to expose the quadratic speed until we get more feedback on whether we want 
to blindly favor complexity over async-safety, or whether people want two 
interfaces, such as memmem which guarantees async-safety, and memmem_fast which 
guarantees speed.

From: Eric Blake <address@hidden>
Date: Fri, 4 Jan 2008 15:19:34 -0700
Subject: [PATCH] Shorten duration of memmem test.

* tests/test-memmem.c (main): Use alarm to declare failure if test
is taking too long.
Reported by Ralf Wildenhues.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog           |   13 ++++++++++---
 tests/test-memmem.c |    6 +++++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 1bba774..f4a48b7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2008-01-04  Eric Blake  <address@hidden>
+
+       Shorten duration of memmem test.
+       * tests/test-memmem.c (main): Use alarm to declare failure if test
+       is taking too long.
+       Reported by Ralf Wildenhues.
+
 2007-12-21  Simon Josefsson  <address@hidden>
 
        * modules/relocatable-prog-wrapper (Depends-on): Add intprops and
@@ -37242,6 +37249,6 @@
        * m4/uintmax_t.m4: New file.
        * m4/Makefile.am (EXTRA_DIST): Add inttypes_h.m4 and uintmax_t.m4.
 
-Copyright (C) 1997-2007 Free Software Foundation, Inc.
+Copyright (C) 1997-2008 Free Software Foundation, Inc.
 Copying and distribution of this file, with or without modification,
 are permitted provided the copyright notice and this notice are preserved.
diff --git a/tests/test-memmem.c b/tests/test-memmem.c
index 50fdfb8..df3baef 100644
--- a/tests/test-memmem.c
+++ b/tests/test-memmem.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2004, 2007 Free Software Foundation
+ * Copyright (C) 2004, 2007, 2008 Free Software Foundation
  * Written by Bruno Haible and Eric Blake
  *
  * This program is free software: you can redistribute it and/or modify
@@ -21,6 +21,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #define ASSERT(expr) \
   do                                                                        \
@@ -36,6 +37,9 @@
 int
 main (int argc, char *argv[])
 {
+  /* Declare failure if test takes too long, by using default abort
+     caused by SIGALRM.  */
+  alarm (10);
   {
     const char input[] = "foo";
     const char *result = memmem (input, strlen (input), "", 0);
-- 
1.5.3.5