use /dev/urandom to generate seed if none is provided

1 files changed, 33 insertions, 4 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 020f46b..67d92e2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,5 +1,9 @@
+#include <array>
 #include <chrono>
 #include <cstdint>
+#include <cstring>
+#include <errno.h>
+#include <fstream>
 #include <print>
 #include <random>
 #include <string>
@@ -18,6 +22,25 @@ void parse_int(std::string_view arg, std::uint64_t &i) {
   }
 }
 
+std::uint64_t random_u64() {
+  std::ifstream ifstream{"/dev/random", std::ios::binary};
+
+  if (!ifstream.is_open()) {
+    throw std::runtime_error(
+        std::format("failed to open /dev/random: {}", std::strerror(errno)));
+  }
+
+  std::array<char, 8> buff;
+
+  ifstream.read(buff.data(), 8);
+
+  std::uint64_t i;
+
+  std::memcpy(&i, buff.data(), 8);
+
+  return i;
+}
+
 int main(int argc, char **argv) {
   if (argc < 3) {
     std::println(stderr, "usage: bench <database> <limit> [seed]");
@@ -27,6 +50,8 @@ int main(int argc, char **argv) {
   auto *path = argv[1];
   auto *limit = argv[2];
 
+  std::println(stderr, "starting benchmark");
+
   std::uint64_t seed;
   if (argc > 3) {
     try {
@@ -36,12 +61,15 @@ int main(int argc, char **argv) {
       return 1;
     }
   } else {
-    seed = std::chrono::system_clock::now().time_since_epoch().count();
+    try {
+      seed = random_u64();
+    } catch (std::exception &e) {
+      std::println(stderr, "{}", e.what());
+      return 1;
+    }
   }
 
-  std::default_random_engine rng{seed};
-
-  std::println(stderr, "starting benchmark");
+  std::println(stderr, "using random seed: {}", seed);
 
   boost::sqlite::connection connection{path};
 
@@ -54,6 +82,7 @@ int main(int argc, char **argv) {
     keys.push_back(key);
   }
 
+  std::default_random_engine rng{seed};
   std::shuffle(keys.begin(), keys.end(), rng);
 
   std::println(stderr, "slurped {} keys into memory", keys.size());