[fpc-pascal] (Unix) file locking

Mark Morgan Lloyd markMLl.fpc-pascal at telemetry.co.uk
Tue Jun 21 10:17:26 CEST 2016


Björn Lundin wrote:
> On 2016-06-21 00:37, Fabio Luis Girardi wrote:> > > 2016-06-20 18:15 GMT-03:00 Björn Lundin <b.f.lundin at gmail.com> <mailto:b.f.lundin at gmail.com>>:> > >     on Linux and AIX I use lockf.>     then read() and write() from the os.>     However I lock the whole file, but the manpage says it is possible to>     lock parts of it.> > >  > This can be used to lock character devices, like /dev/ttyUSB0?> > FPC fpFLock does the same than Posix.Lockf?
> 
> that I do not know.from 'man lockf'DESCRIPTIONApply, test or remove a POSIX lock on a section of an open file.  Thefile is specified by fd, a file descriptor open for writing, the actionby cmd, and the section consists of byte positions pos..pos+len-1 iflen  is positive,  and  pos-len..pos-1 if len is negative, where pos isthe current file position, and if len is zero,the section extends fromthe current file position to infinity, encompassing the present  andfuture  end-of-file positions.  In all cases, the section may extendpast current end-of-file.
> 
> It does not specify underlaying device - but you need an open filedescriptor

The interesting question is what functions that translates to in Pascal 
(specifically, FPC). I suspect FpFcntl() and FpRead() etc. rather than 
anything higher-level (e.g. streams).

-- 
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]


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