Subj : Committing file changes
To   : Coridon Henshaw
From : Herbert Rosenau
Date : Sun Aug 13 2000 12:41 pm

Am 11.08.00 23:38 schrieb Coridon Henshaw

 CH> What's the proper way to 'checkpoint' an open file so as to ensure that 
the
 CH> file's control structures are consistant on disk?  I would have thought
 CH> that calling fflush() after every file write would be sufficient, but a
 CH> recent trap proved that calling fflush() after file writes was no
 CH> protection against CHKDSK truncating the file well before the last write. 
 CH> I suppose I could close and reopen the file after every update, but I was
 CH> hoping to find a more elegant solution.  Any ideas?

Don't use the C runtime! Use DosOpen(....OPEN_FLAGS_WRITE_THROUGH....) and 
other Dos... APIs instead.

The C runtime can't handle OS/2 specific flags. 

fflush() does nothing than flush the runtime buffers - not the 
filesystem/device ones. This means the runtime doen#t always write directly to 
disk. And if it has to do so (eg. fflush() the driver itself doen't it because 
the filesystem cache (cache.exe/diskcache) doesn't it.

If a file is closed the filesystem my delay the last write until the disk is 
idle for a time.

The only way YOU can define exactly that the file is written directly to disk 
is using DosOpen and set the flag. This will disable the cache for that given 
file and all DosWrite goes directly on disk.

But absolutly nothing will get you sure the file is clean if a unpropper reboot 
occures. The only you can do is to hold the window small - AND make a clean 
shutdown.

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