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Fwd: -[NSData writeToFile:atomically:] Bug introduced in 1.5.0


From: Richard Frith-Macdonald
Subject: Fwd: -[NSData writeToFile:atomically:] Bug introduced in 1.5.0
Date: Mon, 16 Sep 2002 15:44:41 +0100


Begin forwarded message:

From: Richard Frith-Macdonald <address@hidden>
Date: Mon Sep 16, 2002  03:43:33 PM Europe/London
To: Roland Schwingel <address@hidden>
Subject: Re: -[NSData writeToFile:atomically:] Bug introduced in 1.5.0


On Monday, September 16, 2002, at 01:38 PM, Roland Schwingel wrote:

Hi....

Im am still migrating sources... And I found I bug which was
(when diffing with base-1.4.0) introduced in base-1.5.0.

On Windows NSDatas -writeToFile:<path> atomically:YES is no longer working. After creating the file it tries to rename() new File to old File. But it can't because
old file is still present....

If you go to line 907: you will find this:

   if ([mgr fileExistsAtPath: path])
   {
     att = [[mgr fileAttributesAtPath: path
                 traverseLink: YES] mutableCopy];
     IF_NO_GC(TEST_AUTORELEASE(att));
   }

In 1.4.0 the source looked like this:

    if ([mgr fileExistsAtPath: path])
   {
     att = [[mgr fileAttributesAtPath: path
                 traverseLink: YES] mutableCopy];
     IF_NO_GC(TEST_AUTORELEASE(att));
     [mgr removeFileAtPath: path handler: nil];
   }

mgr is declared previously. And indeed with 1.5.0 I am getting an errormessage regarding this problem to be
not able to rename the file.

Thanks for the report.

The code in 1.4.0 was wrong ... deleting the file before creating the replacement leaves a (tiny) window during which the file does not exist ... so the operation
was not atomic as it should have been.

The order of operation in 1.5.0 is correct.

However, it seems you have spotted a bug in windoze ... the implementation of rename() does not support replacement of an existing file at the destination
as the posix standard explicitly says it should.

I've modified the code so that it uses a windoze specific call that should do
the replacement.






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