From e1b63d7dec0e5d34940fe275a80c8d88b3e3247e Mon Sep 17 00:00:00 2001
From: topjohnwu <topjohnwu@gmail.com>
Date: Tue, 16 Nov 2021 03:20:07 -0800
Subject: [PATCH] Initialize mt19937 statically in function

This reduces startup time
---
 native/jni/utils/misc.cpp | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/native/jni/utils/misc.cpp b/native/jni/utils/misc.cpp
index 4911b2d74..505c44042 100644
--- a/native/jni/utils/misc.cpp
+++ b/native/jni/utils/misc.cpp
@@ -33,21 +33,17 @@ int fork_no_orphan() {
     return 0;
 }
 
-constexpr char ALPHANUM[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
-static bool seeded = false;
-static std::mt19937 gen;
-static std::uniform_int_distribution<int> dist(0, sizeof(ALPHANUM) - 2);
 int gen_rand_str(char *buf, int len, bool varlen) {
-    if (!seeded) {
+    constexpr char ALPHANUM[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+    static std::mt19937 gen([]{
         if (access("/dev/urandom", F_OK) != 0)
             mknod("/dev/urandom", 0600 | S_IFCHR, makedev(1, 9));
         int fd = xopen("/dev/urandom", O_RDONLY | O_CLOEXEC);
         unsigned seed;
         xxread(fd, &seed, sizeof(seed));
-        gen.seed(seed);
-        close(fd);
-        seeded = true;
-    }
+        return seed;
+    }());
+    std::uniform_int_distribution<int> dist(0, sizeof(ALPHANUM) - 2);
     if (varlen) {
         std::uniform_int_distribution<int> len_dist(len / 2, len);
         len = len_dist(gen);