nghttpx: Use std::shared_ptr to share cached time

To ensure that cached time buffer is not altered while referencing it,
we rely on inerlocking in std::shared_ptr to acheive this.

src/shrpx.cc

@@ -276,16 +276,9 @@ void reopen_log_signal_cb(evutil_socket_t sig, short events, void *arg)
 } // namespace
 
 namespace {
-char time_cache_buf[2][64];
-size_t time_cache_buf_idx = 0;
-} // namespace
-
-namespace {
-const char* cache_time(size_t idx)
+std::unique_ptr<std::string> generate_time()
 {
-  auto buf = time_cache_buf[idx];
-
-  buf[0] = '\0';
+  char buf[32];
 
   // Format data like this:
   // 03/Jul/2014:00:19:38 +0900
@@ -293,24 +286,21 @@ const char* cache_time(size_t idx)
   auto now = time(nullptr);
 
   if(localtime_r(&now, &tms) == nullptr) {
-    return buf;
+    return util::make_unique<std::string>("");
   }
 
-  if(strftime(buf, sizeof(time_cache_buf[0]), "%d/%b/%Y:%T %z", &tms) == 0) {
-    buf[0] = '\0';
-
-    return buf;
+  if(strftime(buf, sizeof(buf), "%d/%b/%Y:%T %z", &tms) == 0) {
+    return util::make_unique<std::string>("");
   }
 
-  return buf;
+  return util::make_unique<std::string>(buf);
 }
 } // namespace
 
 namespace {
 void refresh_cb(evutil_socket_t sig, short events, void *arg)
 {
-  time_cache_buf_idx ^= 1;
-  mod_config()->cached_time = cache_time(time_cache_buf_idx);
+  mod_config()->cached_time = generate_time();
 }
 } // namespace
 
@@ -569,8 +559,7 @@ void fill_default_config()
     (mod_config()->http2_option, 1);
 
   mod_config()->tls_proto_mask = 0;
-  mod_config()->cached_time.store(cache_time(time_cache_buf_idx),
-                                  std::memory_order_release);
+  mod_config()->cached_time = generate_time();
 }
 } // namespace
 

src/shrpx_config.h

@@ -153,6 +153,7 @@ struct Config {
   std::vector<AltSvc> altsvcs;
   std::vector<std::pair<std::string, std::string>> add_response_headers;
   std::vector<unsigned char> alpn_prefs;
+  std::shared_ptr<std::string> cached_time;
   sockaddr_union downstream_addr;
   // binary form of http proxy host and port
   sockaddr_union downstream_http_proxy_addr;
@@ -200,7 +201,6 @@ struct Config {
   FILE *http2_upstream_dump_request_header;
   FILE *http2_upstream_dump_response_header;
   nghttp2_option *http2_option;
-  std::atomic<const char*> cached_time;
   size_t downstream_addrlen;
   size_t num_worker;
   size_t http2_max_concurrent_streams;

src/shrpx_log.cc

@@ -117,9 +117,11 @@ Log::~Log()
   char buf[4096];
   auto tty = worker_config.errorlog_tty;
 
+  auto cached_time = get_config()->cached_time;
+
   rv = snprintf(buf, sizeof(buf),
                 "%s PID%d [%s%s%s] %s\n    %s(%s:%d)%s\n",
-                get_config()->cached_time.load(std::memory_order_acquire),
+                cached_time->c_str(),
                 getpid(),
                 tty ? SEVERITY_COLOR[severity_] : "",
                 SEVERITY_STR[severity_],
@@ -181,9 +183,11 @@ void upstream_accesslog(const std::string& client_ip, unsigned int status_code,
   static const char fmt[] =
     "%s - - [%s] \"%s %s HTTP/%u.%u\" %u %lld \"-\" \"%s\"\n";
 
+  auto cached_time = get_config()->cached_time;
+
   rv = snprintf(buf, sizeof(buf), fmt,
                 client_ip.c_str(),
-                get_config()->cached_time.load(std::memory_order_acquire),
+                cached_time->c_str(),
                 method,
                 path,
                 major,