require et random_device for cons token test

[Jonathan Wakely]

On 24/03/21 03:53 -0300, Alexandre Oliva wrote:
>
>On target systems that don't support any random_device, not even the
>default one,

It should be impossible to have no random_device. As a fallback a
pseudo random number generator should be used.

>other random_device constructor tests are disabled by
>dg-require-effective-target random_device.  The token.cc also
>exercises the default constructor, in a way that doesn't expect an
>exception to be raised, but it's not guarded by the same requirement.
>
>Other potentially-raising ctors in token.cc expect exceptions and
>handle them, but the ("default")-constructed one does not, so the
>program terminates and the test fails without exercising the other
>constructor variants.

Why does the "default" token cause an exception?

>This patch arranges to disable the test altogether when the
>random_device feature is not available.  A reasonable alternative
>would be to install a std::runtime_error handler around the test01
>body, so that we exercise at least the exception raising, but then
>test03 would have to be relaxed, since without even "default", it
>likely wouldn't meet the tested requirement there.
>
>Regstrapped on x86_64-linux-gnu and cross-tested for x86_64-vx7r2 along
>with other patches, mostly for the testsuite.  Ok to install?

No, that would disable the test for Windows, where it works OK.

The 'random_device' effective-target is poorly named, it checks
whether the _GLIBCXX_USE_RANDOM_TR1 macro is defined, which is even
more poorly named. That macro is defined when /dev/random and
/dev/urandom are available. But we support std::random_device without
those files (e.g. on Windows).

If the default constructor throws then that suggests your target is
misconfigured. Why isn't the mt19937 PRNG being used?


>for  libstdc++-v3/ChangeLog
>
>	* testsuite/26_numerics/random/random_device/cons/token.cc:
>	Require effective target feature random_device.
>---
> .../26_numerics/random/random_device/cons/token.cc |    1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc b/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc
>index defb8d58c586a..105ae0ba87743 100644
>--- a/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc
>+++ b/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc
>@@ -1,4 +1,5 @@
> // { dg-do run { target c++11 } }
>+// { dg-require-effective-target random_device }
> // { dg-require-cstdint "" }
> //
> // 2008-11-24  Edward M. Smith-Rowland <3dw4rd@verizon.net>
>
>
>-- 
>Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
>   Free Software Activist         GNU Toolchain Engineer
>        Vim, Vi, Voltei pro Emacs -- GNUlius Caesar
>