Add cross-platform randomizer module.

The code uses two mechanisms for generating random numbers: srand()/rand(),
which is not thread-safe, and srandom()/random(), which is POSIX-specific.

Here I add a util/random.cc module that centralizes these calls, and unifies
some common usage patterns.  If the implementation is not good enough, we can
now change it in a single place.

To keep things simple, this uses the portable srand()/rand() but protects them
with a lock to avoid concurrency problems.

The hard part was to keep the regression tests passing: they rely on fixed
sequences of random numbers, so a small code change could break them very
thoroughly.  Util::rand(), for wide types like size_t, calls std::rand() not
once but twice.  This behaviour was generalized into utils::wide_rand() and
friends.

1 files changed, 3 insertions, 2 deletions

diff --git a/mert/kbmira.cpp b/mert/kbmira.cpp
index 5a119e875..092176984 100644
--- a/mert/kbmira.cpp
+++ b/mert/kbmira.cpp
@@ -40,6 +40,7 @@ de recherches du Canada
 #include <boost/scoped_ptr.hpp>
 
 #include "util/exception.hh"
+#include "util/random.hh"
 
 #include "BleuScorer.h"
 #include "HopeFearDecoder.h"
@@ -122,10 +123,10 @@ int main(int argc, char** argv)
 
   if (vm.count("random-seed")) {
     cerr << "Initialising random seed to " << seed << endl;
-    srand(seed);
+    util::rand_init(seed);
   } else {
     cerr << "Initialising random seed from system clock" << endl;
-    srand(time(NULL));
+    util::rand_init();
   }
 
   // Initialize weights