[gnome-sudoku/gnome-3-20] qqwing-wrapper: Seed RNG

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 30065efc87d381991f51c2a2d39b0ffb0b04425b
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Mon Jul 11 23:15:13 2016 -0500

    qqwing-wrapper: Seed RNG
    
    This is ugly. On the master branch, we will use std::once_flag, but for
    gnome-3-20 let's avoid adding a dependency on C++ 11.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=768345

 lib/qqwing-wrapper.cpp |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)
---
diff --git a/lib/qqwing-wrapper.cpp b/lib/qqwing-wrapper.cpp
index f6602b5..d0eb059 100644
--- a/lib/qqwing-wrapper.cpp
+++ b/lib/qqwing-wrapper.cpp
@@ -41,6 +41,17 @@ int* qqwing_generate_puzzle(int difficulty)
     const int BOARD_SIZE = 81;
     SudokuBoard board;
 
+    // Seed RNG exactly once.
+    static GMutex mutex;
+    static bool seeded = false;
+    g_mutex_lock(&mutex);
+    if (!seeded)
+    {
+        srand(time(nullptr));
+        seeded = true;
+    }
+    g_mutex_unlock(&mutex);
+
     board.setRecordHistory(true);
     board.setLogHistory(false);
     board.setPrintStyle(SudokuBoard::ONE_LINE);