From c834e4c641bf6c73e88b93c0cdba40a83f3192c1 Mon Sep 17 00:00:00 2001
From: Jonas Norlinder <jnorlinder@openjdk.org>
Date: Thu, 8 Jan 2026 16:46:28 +0000
Subject: [PATCH] 8373647: Avoid fstat when opening file for write with
 RandomAccessFile or FileOutputStream

Reviewed-by: redestad, alanb
---
 .../unix/native/libjava/io_util_md.c          | 31 ++++++++++++-------
 .../org/openjdk/bench/java/io/FileWrite.java  | 28 ++++++++++++++++-
 2 files changed, 46 insertions(+), 13 deletions(-)

diff --git a/src/java.base/unix/native/libjava/io_util_md.c b/src/java.base/unix/native/libjava/io_util_md.c
index 2e81cbd05c2..bcac334191c 100644
--- a/src/java.base/unix/native/libjava/io_util_md.c
+++ b/src/java.base/unix/native/libjava/io_util_md.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -27,6 +27,7 @@
 #include "jvm.h"
 #include "io_util.h"
 #include "io_util_md.h"
+#include <fcntl.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -75,20 +76,26 @@ FD
 handleOpen(const char *path, int oflag, int mode) {
     FD fd;
     RESTARTABLE(open(path, oflag, mode), fd);
-    if (fd != -1) {
-        struct stat buf;
-        int result;
-        RESTARTABLE(fstat(fd, &buf), result);
-        if (result != -1) {
-            if (S_ISDIR(buf.st_mode)) {
-                close(fd);
-                errno = EISDIR;
-                fd = -1;
-            }
-        } else {
+    // No further checking is needed if the file is not a
+    // directory or open returned an error
+    if (fd == -1 || ((oflag & O_ACCMODE) != O_RDONLY) != 0) {
+        return fd;
+    }
+
+    // FileInputStream is specified to throw if the
+    // file is a directory
+    struct stat buf;
+    int result;
+    RESTARTABLE(fstat(fd, &buf), result);
+    if (result != -1) {
+        if (S_ISDIR(buf.st_mode)) {
             close(fd);
+            errno = EISDIR;
             fd = -1;
         }
+    } else {
+        close(fd);
+        fd = -1;
     }
     return fd;
 }
diff --git a/test/micro/org/openjdk/bench/java/io/FileWrite.java b/test/micro/org/openjdk/bench/java/io/FileWrite.java
index 21b0c2f8f54..c5a5aee70d8 100644
--- a/test/micro/org/openjdk/bench/java/io/FileWrite.java
+++ b/test/micro/org/openjdk/bench/java/io/FileWrite.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,6 +25,7 @@ package org.openjdk.bench.java.io;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
+import java.io.RandomAccessFile;
 import java.io.IOException;
 import java.util.concurrent.TimeUnit;
 
@@ -81,4 +82,29 @@ public class FileWrite {
         }
     }
 
+    @State(Scope.Benchmark)
+    @Warmup(iterations = 3, time = 2)
+    @Measurement(iterations = 5, time = 5)
+    @BenchmarkMode(Mode.SampleTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    @Threads(1)
+    @Fork(value = 10)
+    public static class OpenFileForWritingBench {
+        final byte[] payload = "something".getBytes();
+        final String path = System.getProperty("os.name", "unknown").toLowerCase().contains("win") ? "NUL" : "/dev/null";
+
+        @Benchmark
+        public void testFileOutputStream() throws IOException {
+            try (FileOutputStream f = new FileOutputStream(path)) {
+                f.write(payload);
+            }
+        }
+
+        @Benchmark
+        public void testRandomAccessFile() throws IOException {
+            try (RandomAccessFile f = new RandomAccessFile(path, "rw")) {
+                f.write(payload);
+            }
+        }
+    }
 }