Open file for exclusive access

Hi,

I would like to open a file for exclusive access for the duration of a
script. If the script fails or finishes the lock must be released.
This is to prevent another user or process from accessing the same
data file. I have googled to no avail.

Thanks in advance

Is this for reading, writing or both
--
Richard Siddaway
Please note that all scripts are supplied "as is" and with no warranty
Blog: http://richardsiddaway.spaces.live.com/
PowerShell User Group: http://www.get-psuguk.org.uk


"char1iecha1k" wrote:

> Hi,
>
> I would like to open a file for exclusive access for the duration of a
> script. If the script fails or finishes the lock must be released.
> This is to prevent another user or process from accessing the same
> data file. I have googled to no avail.
>
> Thanks in advance
>
>

On 15 May, 09:09, RichS <R...@discussions.microsoft.com> wrote:
> Is this for reading, writing or both
> --
> Richard Siddaway
> Please note that all scripts are supplied "as is" and with no warranty
> Blog:http://richardsiddaway.spaces.live.com/
> PowerShell User Group:http://www.get-psuguk.org.uk
>
> "char1iecha1k" wrote:
> > Hi,
>
> > I would like to open a file for exclusive access for the duration of a
> > script. If the script fails or finishes the lock must be released.
> > This is to prevent another user or process from accessing the same
> > data file. I have googled to no avail.
>
> > Thanks in advance

I want to open file for reading, and when open disallow any other
process from opening that file. So far I have this

$test1=new-object System.IO.FileStream("test1.txt",
[System.IO.FileMode]::Open)

Now I need to know how to return the state of the file into a variable
so that my script can move on to the next unopen file ie

for each file in folder open file (if $file already open then return,
else process job)

hope that makes sense

On May 15, 5:11 am, char1iecha1k <charlesgarg...@gmail.com> wrote:
> On 15 May, 09:09, RichS <R...@discussions.microsoft.com> wrote:
>
>
>
>
>
> > Is this for reading, writing or both
> > --
> > Richard Siddaway
> > Please note that all scripts are supplied "as is" and with no warranty
> > Blog:http://richardsiddaway.spaces.live.com/
> > PowerShell User Group:http://www.get-psuguk.org.uk
>
> > "char1iecha1k" wrote:
> > > Hi,
>
> > > I would like to open a file for exclusive access for the duration of a
> > > script. If the script fails or finishes the lock must be released.
> > > This is to prevent another user or process from accessing the same
> > > data file. I have googled to no avail.
>
> > > Thanks in advance
>
> I want to open file for reading, and when open disallow any other
> process from opening that file. So far I have this
>
> $test1=new-object System.IO.FileStream("test1.txt",
> [System.IO.FileMode]::Open)
>
> Now I need to know how to return the state of the file into a variable
> so that my script can move on to the next unopen file ie
>
> for each file in folder open file (if $file already open then return,
> else process job)
>
> hope that makes sense- Hide quoted text -
>
> - Show quoted text -

Do you have control of these other scripts? If so, why not use a
traditional ".lock" file - e.g. when you start up, create a file
called "mydatafile.lock," and delete it when you're finished. All
scripts should look for this while on start up, and quit if it already
exists.

On 15 May, 13:54, Oisin Grehan <ois...@gmail.com> wrote:
> On May 15, 5:11 am, char1iecha1k <charlesgarg...@gmail.com> wrote:
>
>
>
> > On 15 May, 09:09, RichS <R...@discussions.microsoft.com> wrote:
>
> > > Is this for reading, writing or both
> > > --
> > > Richard Siddaway
> > > Please note that all scripts are supplied "as is" and with no warranty
> > > Blog:http://richardsiddaway.spaces.live.com/
> > > PowerShell User Group:http://www.get-psuguk.org.uk
>
> > > "char1iecha1k" wrote:
> > > > Hi,
>
> > > > I would like to open a file for exclusive access for the duration of a
> > > > script. If the script fails or finishes the lock must be released.
> > > > This is to prevent another user or process from accessing the same
> > > > data file. I have googled to no avail.
>
> > > > Thanks in advance
>
> > I want to open file for reading, and when open disallow any other
> > process from opening that file. So far I have this
>
> > $test1=new-object System.IO.FileStream("test1.txt",
> > [System.IO.FileMode]::Open)
>
> > Now I need to know how to return the state of the file into a variable
> > so that my script can move on to the next unopen file ie
>
> > for each file in folder open file (if $file already open then return,
> > else process job)
>
> > hope that makes sense- Hide quoted text -
>
> > - Show quoted text -
>
> Do you have control of these other scripts? If so, why not use a
> traditional ".lock" file - e.g. when you start up, create a file
> called "mydatafile.lock," and delete it when you're finished. All
> scripts should look for this while on start up, and quit if it already
> exists.

Thats the way I do it at the moment. If the script errors for some
unkown reason then the lock file doesnt get removed.

If I open a file in a script as soon as the script ends (due to an
error or natural cause) the file will close.

I have got a bit further, but there are some peculiarities. Here is
the relevant bit of the script :

&{
trap { write-host "error"; exit }
$script:test = new-object System.IO.FileStream("file.lck",
[System.IO.FileMode]::Open)
}
write-host "success"

if the file isnt opened anywhere else then there will be no error in
the script block and the file is opened.
if the file is opened in another process then creating the new object
fails and and the trap handler exits the script.
as soon as the script finishes or exits the filestream is closed

this all works but if you run that piece of code in a test batch file
and keep running it then some times it displays an error and sometimes
not. here is a sample output below

1# gc test.ps1
&{
trap { write-host "error"; exit }
$script:test = new-object System.IO.FileStream("cmdc.lck",
[System.IO.FileMode]::Open)
}
write-host "success"
2# .\test.ps1
success
3# .\test.ps1
success
4# .\test.ps1
success
5# .\test.ps1
error
6# .\test.ps1
success
7# .\test.ps1
error
8# .\test.ps1
success
9# .\test.ps1
error
10# .\test.ps1
success
11# .\test.ps1
error
12# .\test.ps1
success
13# .\test.ps1
success
14# .\test.ps1
error
15# .\test.ps1
error

char1iecha1k wrote:
> On 15 May, 13:54, Oisin Grehan <ois...@gmail.com> wrote:
>> On May 15, 5:11 am, char1iecha1k <charlesgarg...@gmail.com> wrote:
>>
>>
>>
>>> On 15 May, 09:09, RichS <R...@discussions.microsoft.com> wrote:
>>>> Is this for reading, writing or both
>>>> --
>>>> Richard Siddaway
>>>> Please note that all scripts are supplied "as is" and with no warranty
>>>> Blog:http://richardsiddaway.spaces.live.com/
>>>> PowerShell User Group:http://www.get-psuguk.org.uk
>>>> "char1iecha1k" wrote:
>>>>> Hi,
>>>>> I would like to open a file for exclusive access for the duration of a
>>>>> script. If the script fails or finishes the lock must be released.
>>>>> This is to prevent another user or process from accessing the same
>>>>> data file. I have googled to no avail.
>>>>> Thanks in advance
>>> I want to open file for reading, and when open disallow any other
>>> process from opening that file. So far I have this
>>> $test1=new-object System.IO.FileStream("test1.txt",
>>> [System.IO.FileMode]::Open)
>>> Now I need to know how to return the state of the file into a variable
>>> so that my script can move on to the next unopen file ie
>>> for each file in folder open file (if $file already open then return,
>>> else process job)
>>> hope that makes sense- Hide quoted text -
>>> - Show quoted text -
>> Do you have control of these other scripts? If so, why not use a
>> traditional ".lock" file - e.g. when you start up, create a file
>> called "mydatafile.lock," and delete it when you're finished. All
>> scripts should look for this while on start up, and quit if it already
>> exists.
>
> Thats the way I do it at the moment. If the script errors for some
> unkown reason then the lock file doesnt get removed.
>
> If I open a file in a script as soon as the script ends (due to an
> error or natural cause) the file will close.
>
> I have got a bit further, but there are some peculiarities. Here is
> the relevant bit of the script :
>
> &{
> trap { write-host "error"; exit }
> $script:test = new-object System.IO.FileStream("file.lck",
> [System.IO.FileMode]::Open)
> }
> write-host "success"
>
> if the file isnt opened anywhere else then there will be no error in
> the script block and the file is opened.
> if the file is opened in another process then creating the new object
> fails and and the trap handler exits the script.
> as soon as the script finishes or exits the filestream is closed
>
> this all works but if you run that piece of code in a test batch file
> and keep running it then some times it displays an error and sometimes
> not. here is a sample output below
>
> 1# gc test.ps1
> &{
> trap { write-host "error"; exit }
> $script:test = new-object System.IO.FileStream("cmdc.lck",
> [System.IO.FileMode]::Open)
> }
> write-host "success"
> 2# .\test.ps1
> success
> 3# .\test.ps1
> success
> 4# .\test.ps1
> success
> 5# .\test.ps1
> error
> 6# .\test.ps1
> success
> 7# .\test.ps1
> error
> 8# .\test.ps1
> success
> 9# .\test.ps1
> error
> 10# .\test.ps1
> success
> 11# .\test.ps1
> error
> 12# .\test.ps1
> success
> 13# .\test.ps1
> success
> 14# .\test.ps1
> error
> 15# .\test.ps1
> error
>
>
>

Sounds like you need to set your PSH script to continue even if there's
a failure of any sorts so the lock gets created, then removed even if
any commands within it fail?

http://blogs.msdn.com/powershell/arc...25/583241.aspx

On 15 May, 15:19, Marco Shaw <marco.shaw@_NO_SPAM_gmail.com> wrote:
> char1iecha1k wrote:
> > On 15 May, 13:54, Oisin Grehan <ois...@gmail.com> wrote:
> >> On May 15, 5:11 am, char1iecha1k <charlesgarg...@gmail.com> wrote:
>
> >>> On 15 May, 09:09, RichS <R...@discussions.microsoft.com> wrote:
> >>>> Is this for reading, writing or both
> >>>> --
> >>>> Richard Siddaway
> >>>> Please note that all scripts are supplied "as is" and with no warranty
> >>>> Blog:http://richardsiddaway.spaces.live.com/
> >>>> PowerShell User Group:http://www.get-psuguk.org.uk
> >>>> "char1iecha1k" wrote:
> >>>>> Hi,
> >>>>> I would like to open a file for exclusive access for the duration of a
> >>>>> script. If the script fails or finishes the lock must be released.
> >>>>> This is to prevent another user or process from accessing the same
> >>>>> data file. I have googled to no avail.
> >>>>> Thanks in advance
> >>> I want to open file for reading, and when open disallow any other
> >>> process from opening that file. So far I have this
> >>> $test1=new-object System.IO.FileStream("test1.txt",
> >>> [System.IO.FileMode]::Open)
> >>> Now I need to know how to return the state of the file into a variable
> >>> so that my script can move on to the next unopen file ie
> >>> for each file in folder open file (if $file already open then return,
> >>> else process job)
> >>> hope that makes sense- Hide quoted text -
> >>> - Show quoted text -
> >> Do you have control of these other scripts? If so, why not use a
> >> traditional ".lock" file - e.g. when you start up, create a file
> >> called "mydatafile.lock," and delete it when you're finished. All
> >> scripts should look for this while on start up, and quit if it already
> >> exists.
>
> > Thats the way I do it at the moment. If the script errors for some
> > unkown reason then the lock file doesnt get removed.
>
> > If I open a file in a script as soon as the script ends (due to an
> > error or natural cause) the file will close.
>
> > I have got a bit further, but there are some peculiarities. Here is
> > the relevant bit of the script :
>
> > &{
> > trap { write-host "error"; exit }
> > $script:test = new-object System.IO.FileStream("file.lck",
> > [System.IO.FileMode]::Open)
> > }
> > write-host "success"
>
> > if the file isnt opened anywhere else then there will be no error in
> > the script block and the file is opened.
> > if the file is opened in another process then creating the new object
> > fails and and the trap handler exits the script.
> > as soon as the script finishes or exits the filestream is closed
>
> > this all works but if you run that piece of code in a test batch file
> > and keep running it then some times it displays an error and sometimes
> > not. here is a sample output below
>
> > 1# gc test.ps1
> > &{
> > trap { write-host "error"; exit }
> > $script:test = new-object System.IO.FileStream("cmdc.lck",
> > [System.IO.FileMode]::Open)
> > }
> > write-host "success"
> > 2# .\test.ps1
> > success
> > 3# .\test.ps1
> > success
> > 4# .\test.ps1
> > success
> > 5# .\test.ps1
> > error
> > 6# .\test.ps1
> > success
> > 7# .\test.ps1
> > error
> > 8# .\test.ps1
> > success
> > 9# .\test.ps1
> > error
> > 10# .\test.ps1
> > success
> > 11# .\test.ps1
> > error
> > 12# .\test.ps1
> > success
> > 13# .\test.ps1
> > success
> > 14# .\test.ps1
> > error
> > 15# .\test.ps1
> > error
>
> Sounds like you need to set your PSH script to continue even if there's
> a failure of any sorts so the lock gets created, then removed even if
> any commands within it fail?
>
> http://blogs.msdn.com/powershell/arc...25/583241.aspx

I don't wont to continue if the file is already open. If the file is
not open then I want to open it.

If after that the script fails or finishes naturally then the I want
the filestream to close, which it does most of the time, but as shown
above sometimes it doesn't work properly. I have executed the script
manually (once every second) to produce the output above. Even when
leaving a good 5 seconds between executions it still sometimes errors.
This shouldn't happen, if it should then I need to know why and how to
avoid it

"char1iecha1k" <charlesgargent@gmail.com> wrote in message
news:1179176871.496647.42740@l77g2000hsb.googlegroups.com...
> Hi,
>
> I would like to open a file for exclusive access for the duration of a
> script. If the script fails or finishes the lock must be released.
> This is to prevent another user or process from accessing the same
> data file. I have googled to no avail.
>
> Thanks in advance
>

Perhaps you should try this FileStream constructor:

public FileStream (
string path,
FileMode mode,
FileAccess access,
FileShare share
)

And set the share parameter to FileShare.None.

--
Keith

Keith Hill wrote:
> "char1iecha1k" <charlesgargent@gmail.com> wrote in message
> news:1179176871.496647.42740@l77g2000hsb.googlegroups.com...
>> Hi,
>>
>> I would like to open a file for exclusive access for the duration of
>> a script. If the script fails or finishes the lock must be released.
>> This is to prevent another user or process from accessing the same
>> data file. I have googled to no avail.
>>
>> Thanks in advance
>>
>
> Perhaps you should try this FileStream constructor:
>
> public FileStream (
> string path,
> FileMode mode,
> FileAccess access,
> FileShare share
> )
>
> And set the share parameter to FileShare.None.

Good suggestion,

Is the FileShare.None option enough to lock the file or should one call $fileStream.Lock(0,$filestream.Length-1)?

And how about unlocking the file, will dereferencing the FileStream lift the lock, or is an explicit call to unlock required/recommended?


--
Joris van Lier
Please note that all scripts and opinions are supplied "as is" and with
no warranty Blog: http://whizzrd.spaces.live.com

If you use the FileShare parameter then the file will be locked to anyone
else until the file is closed (by disposing of the FileStream). The
Lock/Unlock methods allow you lock/unlock certain regions of a file where
that file allows write access to others.

--
Keith

"Joris van Lier" <whizzrd@hotmail.com> wrote in message
news:etPbqbwlHHA.4188@TK2MSFTNGP02.phx.gbl...
Keith Hill wrote:
> "char1iecha1k" <charlesgargent@gmail.com> wrote in message
> news:1179176871.496647.42740@l77g2000hsb.googlegroups.com...
>> Hi,
>>
>> I would like to open a file for exclusive access for the duration of
>> a script. If the script fails or finishes the lock must be released.
>> This is to prevent another user or process from accessing the same
>> data file. I have googled to no avail.
>>
>> Thanks in advance
>>
>
> Perhaps you should try this FileStream constructor:
>
> public FileStream (
> string path,
> FileMode mode,
> FileAccess access,
> FileShare share
> )
>
> And set the share parameter to FileShare.None.

Good suggestion,

Is the FileShare.None option enough to lock the file or should one call
$fileStream.Lock(0,$filestream.Length-1)?

And how about unlocking the file, will dereferencing the FileStream lift the
lock, or is an explicit call to unlock required/recommended?


--
Joris van Lier
Please note that all scripts and opinions are supplied "as is" and with
no warranty Blog: http://whizzrd.spaces.live.com