Optimize CloseAllFdsOnExec for large MaxOpenFiles

1 files changed, 16 insertions, 2 deletions

diff --git a/util/system/shellcommand.cpp b/util/system/shellcommand.cpp
index 025a3ffd2f..03c78b4d92 100644
--- a/util/system/shellcommand.cpp
+++ b/util/system/shellcommand.cpp
@@ -687,8 +687,22 @@ void TShellCommand::TImpl::OnFork(TPipes& pipes, sigset_t oldmask, char* const*
         }
 
         if (Options_.CloseAllFdsOnExec) {
-            for (int fd = NSystemInfo::MaxOpenFiles(); fd > STDERR_FILENO; --fd) {
-                fcntl(fd, F_SETFD, FD_CLOEXEC);
+            int maxOpenFiles = NSystemInfo::MaxOpenFiles();
+            TFsPath fdDir("/proc/self/fd");
+            // For a big MaxOpenFiles value directory listing overhead is negligible against useless fcntl calls
+            if (maxOpenFiles > 1024 && fdDir.IsDirectory()) {
+                TVector<TString> files;
+                fdDir.ListNames(files);
+                for (const TString& f : files) {
+                    int fd;
+                    if (TryFromString(f, fd) && fd > STDERR_FILENO) {
+                        fcntl(fd, F_SETFD, FD_CLOEXEC);
+                    }
+                }
+            } else {
+                for (int fd = maxOpenFiles; fd > STDERR_FILENO; --fd) {
+                    fcntl(fd, F_SETFD, FD_CLOEXEC);
+                }
             }
         }