Thread-safe, platform-agnostic randomizer.

Some places in mert use srandom()/random(), but these are POSIX-specific.
The standard alternative, srand()/rand(), is not thread-safe.  This module
wraps srand()/rand() in mutexes (very short-lived, so should not cost much)
so that it relies on just Boost and the C standard library, not on a Unix-like
environment.

This may reduce the width of the random numbers on some platforms: it goes
from "long int" to just "int".  If that is a problem, we may have to use
Boost's randomizer utilities, or eventually, the C++ ones.

1 files changed, 39 insertions, 0 deletions

diff --git a/util/random_test.cc b/util/random_test.cc
new file mode 100644
index 000000000..d1c555a0c
--- /dev/null
+++ b/util/random_test.cc
@@ -0,0 +1,39 @@
+#include "util/random.hh"
+
+#define BOOST_TEST_MODULE RandomTest
+#include <boost/test/unit_test.hpp>
+
+namespace util
+{
+namespace
+{
+
+BOOST_AUTO_TEST_CASE(returns_different_consecutive_numbers)
+{
+  rand_int_init(99);
+  const int first = rand_int(), second = rand_int(), third = rand_int();
+  // Sometimes you'll get the same number twice in a row, but generally the
+  // randomizer returns different numbers.
+  BOOST_CHECK(second != first || third != first);
+}
+
+BOOST_AUTO_TEST_CASE(returns_different_numbers_for_different_seeds)
+{
+  rand_int_init(1);
+  const int one1 = rand_int(), one2 = rand_int();
+  rand_int_init(2);
+  const int two1 = rand_int(), two2 = rand_int();
+  BOOST_CHECK(two1 != one1 || two2 != two1);
+}
+
+BOOST_AUTO_TEST_CASE(returns_same_sequence_for_same_seed)
+{
+  rand_int_init(1);
+  const int first = rand_int();
+  rand_int_init(1);
+  const int second = rand_int();
+  BOOST_CHECK_EQUAL(first, second);
+}
+
+} // namespace
+} // namespace util