cvs commit: src/lib/libutil pidfile.c

Colin Percival cperciva at
Wed Apr 12 07:31:28 UTC 2006

Pawel Jakub Dawidek wrote:
> On Tue, Apr 11, 2006 at 11:10:02PM +0000, John-Mark Gurney wrote:
> +>   use pwrite to always write at the begining of the file..  If multiple calls
> +>   to pidfile_write happen, the pidfile will have nul characters prepended
> +>   due to the cached file descriptor offset...
> Multiple pidfile_write()s from the same process? If not, then we must
> truncate the file before writting the PID.

We already do -- there's a call to ftruncate(fd, 0) a few lines earlier.

> Imagine a situation, where PID 10000 is written first and then we
> overwrite it with 9999. The result will be 99990.

The only way this can happen is if two different processes call
pidfile_write simultaneously and both ftruncate calls complete
before either pwrite call starts; I don't think this is really
worth worrying about.

Colin Percival

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