Thread-safe file locking

**Ian Collins** · Sep 15 '07, 01:45 AM

Re: Thread-safe file locking

Matt Brandt wrote:

I am trying to get multiple threads to lock specific regions of a file.
However, since each thread has the same PID, it appears that a lock by
one thread does not block another thread from the same process.
>
How does one maintain file locking between sibling threads?
>

comp.programmin g.threads or an OS programming group would be a more
appropriate place to ask this. Neither C nor C++ have standard thread
or file locking support.

--
Ian Collins.

**Ron AF Greve** · Sep 15 '07, 11:35 AM

Re: Thread-safe file locking

Hi,

Maybe use a piece of code in your program to keep track of which thread
locked which region. Protrecting that piece of code with a mutex. Most
system support mutexes ( for instance sunos, MS-Windows and I believe linux)
..

Regards, Ron AF Greve

http://www.InformationSuperHighway.eu

"Ian Collins" <ian-news@hotmail.co mwrote in message
news:5l0rieF5q9 24U1@mid.indivi dual.net...

Matt Brandt wrote:

>I am trying to get multiple threads to lock specific regions of a file.
>However, since each thread has the same PID, it appears that a lock by
>one thread does not block another thread from the same process.
>>
>How does one maintain file locking between sibling threads?
>>

comp.programmin g.threads or an OS programming group would be a more
appropriate place to ask this. Neither C nor C++ have standard thread
or file locking support.
>
--
Ian Collins.

**Rolf Magnus** · Sep 15 '07, 12:15 PM

Re: Thread-safe file locking

Matt Brandt wrote:

I am trying to get multiple threads to lock specific regions of a file.
However, since each thread has the same PID, it appears that a lock by
one thread does not block another thread from the same process.
>
How does one maintain file locking between sibling threads?

Both Standard C and C++ assume that there is nothing else running besides
your program, and both languages don't support threads. Therefore, there is
no concept of "file locking". To do what you want, you have to resort to
system-specific libraries.

**CBFalconer** · Sep 15 '07, 02:35 PM

Re: Thread-safe file locking

Matt Brandt wrote:

>
I am trying to get multiple threads to lock specific regions of a
file. However, since each thread has the same PID, it appears that
a lock by one thread does not block another thread from the same
process.
>
How does one maintain file locking between sibling threads?

Both threads and C++ are off-topic here (on c.l.c). We never heard
of a PID either. F'ups set.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>

--
Posted via a free Usenet account from http://www.teranews.com

ks · Sep 15 '07, 03:15 PM

Re: Thread-safe file locking

On Sep 14, 9:38 pm, CBFalconer <cbfalco...@yah oo.comwrote:

Matt Brandt wrote:
>

I am trying to get multiple threads to lock specific regions of a
file. However, since each thread has the same PID, it appears that
a lock by one thread does not block another thread from the same
process.

>

How does one maintain file locking between sibling threads?

>
Both threads and C++ are off-topic here (on c.l.c). We never heard
of a PID either. F'ups set.

Is your advertisement off topic?

**Ian Collins** · Sep 15 '07, 08:25 PM

Re: Thread-safe file locking

Ron AF Greve wrote:

Please stop top posting. Your reply wasn't even a follow up to mine.

--
Ian Collins.

**Matt Brandt** · Sep 15 '07, 09:15 PM

Re: Thread-safe file locking

OK, well which ones then?

On 15 Sep 2007 at 12:06, Rolf Magnus wrote:

Matt Brandt wrote:
>

>I am trying to get multiple threads to lock specific regions of a file.
>However, since each thread has the same PID, it appears that a lock by
>one thread does not block another thread from the same process.
>>
>How does one maintain file locking between sibling threads?

>
Both Standard C and C++ assume that there is nothing else running besides
your program, and both languages don't support threads. Therefore, there is
no concept of "file locking". To do what you want, you have to resort to
system-specific libraries.
>

**Walter Roberson** · Sep 15 '07, 09:25 PM

Re: Thread-safe file locking

In article <slrnfeoimm.8vs .spamoff@nospam .invalid>,
Matt Brandt <mattg@mailinat or.comtop-posted

>On 15 Sep 2007 at 12:06, Rolf Magnus wrote:

>Matt Brandt wrote:

>>I am trying to get multiple threads to lock specific regions of a file.

>To do what you want, you have to resort to
>system-specific libraries.

>OK, well which ones then?

Putting on my mind-reading hat....

....
...
...
...
Got it!

On your system, you need nerf_lock(), quizzle84(),
and (especially), StopTopPosting( )
--
"law -- it's a commodity"
-- Andrew Ryan (The Globe and Mail, 2005/11/26)

**Duane Hebert** · Sep 15 '07, 09:45 PM

Re: Thread-safe file locking

"Matt Brandt" <mattg@mailinat or.comwrote in message
news:slrnfeoimm .8vs.spamoff@no spam.invalid...

OK, well which ones then?

Boost has a thread library. Qt has one as well. Hard to say without
knowing what you use.

**Ian Collins** · Sep 15 '07, 10:25 PM

Re: Thread-safe file locking

Duane Hebert wrote:

"Matt Brandt" <mattg@mailinat or.comwrote in message
news:slrnfeoimm .8vs.spamoff@no spam.invalid...

>OK, well which ones then?

>
Boost has a thread library. Qt has one as well. Hard to say without
knowing what you use.
>

Or even which language...

--
Ian Collins.

**Duane Hebert** · Sep 15 '07, 11:35 PM

Re: Thread-safe file locking

"Ian Collins" <ian-news@hotmail.co mwrote in message
news:5l33upF5iu s4U20@mid.indiv idual.net...

Duane Hebert wrote:

>"Matt Brandt" <mattg@mailinat or.comwrote in message
>news:slrnfeoim m.8vs.spamoff@n ospam.invalid.. .

>>OK, well which ones then?

>>
>Boost has a thread library. Qt has one as well. Hard to say without
>knowing what you use.
>>

Or even which language...

Missed the cross post. If the OP is using C only,
pretty much lets out my suggestions...

**Gianni Mariani** · Sep 16 '07, 03:05 AM

Re: Thread-safe file locking

Matt Brandt wrote:

I am trying to get multiple threads to lock specific regions of a file.
However, since each thread has the same PID, it appears that a lock by
one thread does not block another thread from the same process.
>
How does one maintain file locking between sibling threads?

You should not be using file locking to protect between the same
threads. On the other hand, if the file handles are different, it may
be that file locking will work even within the same thread on different
file handles.

**Walter Roberson** · Sep 16 '07, 04:25 AM

Re: Thread-safe file locking

In article <46ec99f1$0$324 51$5a62ac22@per-qv1-newsreader-01.iinet.net.au >,
Gianni Mariani <gi3nospam@mari ani.wswrote:

>Matt Brandt wrote:

>I am trying to get multiple threads to lock specific regions of a file.
>However, since each thread has the same PID, it appears that a lock by
>one thread does not block another thread from the same process.

>How does one maintain file locking between sibling threads?

>You should not be using file locking to protect between the same
>threads. On the other hand, if the file handles are different, it may
>be that file locking will work even within the same thread on different
>file handles.

Unfortunately your answer to this off-topic question was not correct.
POSIX, for example, defines most attributes as being related to
the file descriptor (fd), not the file handle (FILE*) --
but when it comes to POSIX locking:

NOTES
Locks are on files, not file descriptors. That is, file descriptors
duplicated through dup(3C) (but not through fork(2), see the BUGS section
below) do not result in multiple instances of a lock, but rather multiple
references to a single lock.

This has some interesting and probably unintended consequences that can
result in early loss of the lock.

Correct locking is platform specific, and needs to be referred to
a platform specific newsgroup.
--
"It is important to remember that when it comes to law, computers
never make copies, only human beings make copies. Computers are given
commands, not permission. Only people can be given permission."
-- Brad Templeton

**Richard** · Sep 16 '07, 07:35 PM

Re: Thread-safe file locking

CBFalconer <cbfalconer@yah oo.comwrites:

Matt Brandt wrote:

>>
>I am trying to get multiple threads to lock specific regions of a
>file. However, since each thread has the same PID, it appears that
>a lock by one thread does not block another thread from the same
>process.
>>
>How does one maintain file locking between sibling threads?

>
Both threads and C++ are off-topic here (on c.l.c). We never heard
of a PID either. F'ups set.

Really? You must be a hobbyist programmer.

I have never heard of "F'ups".

"We" speak English is this news group. Kindly be courteous and consider
people whose first language is not English and would have problems
decoding your awful tendency to "jive" in your replies.

>
--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>

Thread-safe file locking

Thread-safe file locking

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