From 4bd026cccb2c22279dd9c88e704642c5a65d3c53 Mon Sep 17 00:00:00 2001
From: Michael Santos <michael.santos@gmail.com>
Date: Fri, 30 Apr 2010 12:22:11 -0400
Subject: Support opening files in exclusive mode

Add an option that atomically tests for the existence of a file and
creates it if the file does not exist, by passing the O_EXCL flag
to open() on Unix and CREATE_NEW flag on Windows. Support for O_EXCL
varies across platforms and filesystems.

{ok, Fd} = file:open("/tmp/foo", [write,exclusive]),
{error, eexist} = file:open("/tmp/foo", [write,exclusive]).
---
 lib/kernel/doc/src/file.xml | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

(limited to 'lib/kernel/doc')

diff --git a/lib/kernel/doc/src/file.xml b/lib/kernel/doc/src/file.xml
index 382262d1ee..a9ceac0bcf 100644
--- a/lib/kernel/doc/src/file.xml
+++ b/lib/kernel/doc/src/file.xml
@@ -603,7 +603,7 @@ f.txt:  {person, "kalle", 25}.
       <type>
         <v>Filename = name()</v>
         <v>Modes = [Mode]</v>
-        <v>&nbsp;Mode = read | write | append | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed</v>
+        <v>&nbsp;Mode = read | write | append | exclusive | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed</v>
         <v>&nbsp;&nbsp;Size = Delay = int()</v>
         <v>IoDevice = io_device()</v>
         <v>Reason = ext_posix() | system_limit</v>
@@ -630,6 +630,17 @@ f.txt:  {person, "kalle", 25}.
               file opened with <c>append</c> will take place at
               the end of the file.</p>
           </item>
+          <tag><c>exclusive</c></tag>
+          <item>
+            <p>The file, when opened for writing, is created if it
+              does not exist. If the file exists, open will return
+              <c>{error, eexist}</c>.</p>
+	    <warning><p>This option does not guarantee exclusiveness on
+	    file systems that do not support O_EXCL properly,
+	    such as NFS. Do not depend on this option unless you
+	    know that the file system supports it (in general, local
+	    file systems should be safe).</p></warning>
+          </item>
           <tag><c>raw</c></tag>
           <item>
             <p>The <c>raw</c> option allows faster access to a file,
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