Add voluntary spin lock for logging to reduce conflicts with stderr.

tdutils/td/utils/AsyncFileLog.cpp

@@ -40,7 +40,6 @@ Status AsyncFileLog::init(string path, int64 rotate_threshold, bool redirect_std
   logging_thread_ = td::thread(
       [queue = queue_.get(), fd = std::move(fd), path = path_, size, rotate_threshold, redirect_stderr]() mutable {
         auto after_rotation = [&] {
-          ScopedDisableLog disable_log;  // to ensure that nothing will be printed to the closed log
           fd.close();
           auto r_fd = FileFd::open(path, FileFd::Create | FileFd::Write | FileFd::Append);
           if (r_fd.is_error()) {
@@ -61,6 +60,12 @@ Status AsyncFileLog::init(string path, int64 rotate_threshold, bool redirect_std
             after_rotation();
           }
           while (!slice.empty()) {
+            if (redirect_stderr) {
+              auto &guard = get_log_guard();
+              while (guard.load() != 0) {
+                // spin
+              }
+            }
             auto r_size = fd.write(slice);
             if (r_size.is_error()) {
               process_fatal_error(PSLICE() << r_size.error() << " in " << __FILE__ << " at " << __LINE__ << '\n');

tdutils/td/utils/FileLog.cpp

@@ -82,6 +82,12 @@ void FileLog::do_append(int log_level, CSlice slice) {
     do_after_rotation();
   }
   while (!slice.empty()) {
+    if (redirect_stderr_) {
+      auto &guard = get_log_guard();
+      while (guard.load() != 0) {
+        // spin
+      }
+    }
     auto r_size = fd_.write(slice);
     if (r_size.is_error()) {
       process_fatal_error(PSLICE() << r_size.error() << " in " << __FILE__ << " at " << __LINE__ << '\n');

tdutils/td/utils/logging.cpp

@@ -250,6 +250,11 @@ void process_fatal_error(CSlice message) {
   std::abort();
 }
 
+std::atomic<uint32> &get_log_guard() {
+  static std::atomic<uint32> log_guard;
+  return log_guard;
+}
+
 namespace {
 std::mutex sdl_mutex;
 int sdl_cnt = 0;

tdutils/td/utils/logging.h

@@ -221,6 +221,8 @@ class Logger {
   int log_level_;
 };
 
+std::atomic<uint32> &get_log_guard();
+
 class ScopedDisableLog {
  public:
   ScopedDisableLog();