I want to write to/delete a file but sometimes I get a crash if the file is in use by another program. How do I check to see whether the file is opened by another process or I can open it for writing?
The problem is, that between the time you check to see if you could get exclusive access and opening the file, something else gets exclusive access to the file, and you get the exception anyway.
The only fool proof way to see if you can get an exclusive lock on a file is to try and get an exclusive lock on the file, if you get it you have it.
If not, you catch the exception, and either
Go do something else
Wait a while and try again
It's one of life’s situations where it's better to ask for forgiveness than permission :)
There is a new way to get the origin of file locking for Vista and up here:
http://www.remkoweijnen.nl/blog/2011/01/03/cannot-access-files-but-need-the-origin/
UserMode:
The best way to write to a locked file is to ask the user to close it in the other process. In batch processes you should ignore such a file and log the problem. Providing the name of the other process is a very good way to find a solution for the user.
Not sure in which programming language you'd like to check if you can write to a file. In Java, java.io.File.canWrite() can do the job for you.
General:
In UNIX-like OS, you can use the lsof command.
If you want to see which program holds a handle to your file, use the Process Monitor (download from MicroSoft).
This tool has a command line interface, so you could use your language's scripting interface (for example java.lang.Process) to run the tool and display a useful error message.
IsFileInUse as given in http://delphi.about.com/cs/adptips1999/a/bltip0999_3.htm
Related
Is there any way of persisting my F# session or serializing it into a file? i.e. so I can hand it to a friend and say "run this" and they will be at the same place I was? I know forth had this ability but I can't find any way of doing this.
An alternative would be a log file or something of similar ilk, but ideally it would strip the output and just give me the code I wrote.
On the topic of user questions, is there a config file for F# so I can add some "always includes" or alter the defaults?
There is no way to serialize the F# Interactive session or create some log of commands automatically.
The typical user interaction is that you write all your code in F# Script File (.fsx extension) and evaluate code by selecting lines and sending them to F# Interactive using Alt+Enter. If you work like this, then the F# Script File is a bit like log of your work - and you can easily send it to other people.
The good thing about this approach is that you can edit the file - if you write something wrong, you can correct it and the wrong version will not appear in the log. The bad thing is that you need some additional effort to keep the source file correct.
Regarding automatic inclusions - you can specify options for fsi.exe in Visual Studio Options (F# Tools). The --load command line parameter can be used to load some F# source at startup.
Is there any way to delete a file when its using by any program or other process in windows?
I searched and found this 2 ways:
1- using RunOnce key in Registry;
I'm not gonna use this because i dont want to wait for windows restart or anything else... prefer to do it ontime!
2- using the way declared in this page: http://www.delphipages.com/forum/showthread.php?t=201190
the problem here is its useful under NT windows, i need a way works on all Windowses!
Thank you.
the problem here is its useful under NT windows, i need a way works on all Windowses!
All modern desktop Windowses (XP, Vista, 7) are also NT. Do you really need to work with NT<4 or Win98? Or even Win CE/Mobile/Phone? Probably not.
If you need to delete an open file straight away, about the only thing you can do is attach to each process using debugger privileges, see if it has any handles open on the file, and if so close them underneath it. You can do this the manual way using eg Process Explorer. Many applications won't react well to having their files closed on them; expect them to exception out when they try to do something with the dead handle.
Unfortunately there is no option in Windows to have Unix-style files that can exist attached to a file handle independently of being stored under a filename on disc.
You cant delete a file when someone is using it. No matter how hard you try, windows will not let you. It can work with some files, but in general it does not work.
What you can try is postpone the deletion, when no one is using the file. You can:
1 - use RunOnce, but you dont want that.
2 - Wait in a loop, trying to delete the file. Pseudo code:
DeleteFile
Check if you was able to delete or if file still exists.
if you are able to delete, then exit loop.
That is the best you can do, and what i could remeber.
Try MoveFileEx with MOVEFILE_DELAY_UNTIL_REBOOT flag. Will postpone move or delete action until reboot.
Edit:
If you don't whant to restart the only option is to close those handles. ProcessExplorer does that and works all the time and I have not seen any process to crash. See more info about enumeration handles in a process at
http://www.codeguru.com/forum/archive/index.php/t-176997.html. But keep in mint that you should enumerate all processes in the system and behave different on Vista+ (you need to be elevated)
Your files are most likely locked because some process has a handle open to them. That is the most common reason for the Access denied result when deleting or moving a file.
A really blunt way is to close that handle.
Then Handles tool from SysInternals (you can download the sources too) can do that for you: I have been successfully using that.
Note 1: You need administrative privileges to use it.
Note 2: Closing a handle from another process is considered very rude, and can make that process unstable.
I am using someone else's library that provides its own scripting host instance, it appears.
This lib provides me with functions to define the type of scripting language such as "jscript" and "vbscript", and I can supply it with script code and have that executed, with passing arguments in and back. So, basically, it works.
However, when I try to access the "WScript" object, I get an exception saying that this keyword is undefined.
The developer, not knowing much about this either (he only made this lib for me because I do not want to deal with Windows SDKs right now), told me that he is using "IScriptControl" for this.
Oh, and the lib also provides flags to allow "only safe subset" and "allow UI", which I set to false and true, respectively.
Does that ring a bell with anyone? Do a user of IScriptControl have to take extra steps in order to make a WScript object available? Or, can he use IScriptControl in a way that this is supplied automatically, just as when running the same script from wscript.exe?
Basically, all I need is the WScript.CreateObject function in order to access another app's API via COM.
I don't know why WScript is not known, but I suspect it is because the script host doesn't provide it. Maybe only wscript.exe does this.
If you are using Javascript, to create an object you can use new ActiveXObject(). If you are using VBScript, you can just use CreateObject.
See this article for some background.
A very simple situation. I'm working on an application in Delphi 2007 which is often compiled as 'Release' but still runs under a debugger. And occasionally it will run under SilkTest too, for regression testing. While this is quite fun I want to do something special...
I want to detect if my application is running within a debugger/regression-tester and if that's the case, I want the application to know which tool is used! (Thus, when the application crashes, I could report this information in it's error report.)
Any suggestions, solutions?
You can check the parent process that started your application.
With CreateToolhelp32Snapshot/Process32First/Process32Next get the parent PID (PROCESSENTRY32.th32ParentProcessID or TProcessEntry32.th32ParentProcessID) for your application PID. Then get the filename for the parent PID to compare with the applications you want to check for, like SilkTest.
Check this article for code usage.
In addition to IsDebuggerPresent and CheckRemoteDebuggerPresent, you can also query PEB.BeingDebugged (PEB is Process Environment Block, to get PEB you must query TEB, which is the Thread Enviroment Block).
You're probably looking for the IsDebuggerPresent function.
To detect SilkTest, you could try to attach to a DLL which is used only by SilkTest in order to detect its presence. For example, if the Open Agent is attached to a process, Win32HookDll_x86.dll or Win32HookDll_amd64.dll will be present (the names can be easily found out with a tool like Process Explorer.
You can also do
if DebugHook <> 0 then ...
Is is possible to open a text file and read the contents while another application is updating the file, in such a way that it does not cause a lock conflict?
I need to monitor a log file from one application which is updated by another application each time an event occurs.
I do check if the file is in use before I try to read it, but that does not seem to work in all cases.
Thanks, Pieter
it depends on how the first app open that file.
i.e when calling CreateFile API to open a file, there is dwShareMode param which tells the api how to open it (if this was given 0, it can't be accessed from other applications IIRC).
otherwise there should be no problem with reading from that file.
if im not mistaken, to check if that file is being opened read only u can call
something like
CreateFile(pchar(fName), GENERIC_READ or GENERIC_WRITE, 0, nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0) ;
Download Process Monitor from Sysinternals.
Open the filter dialog and add a "path" filter for your log file.
Start the log-writing application (I'll call this "logwriter").
Look for and click on the event where logwriter does a CreateFile.
Under "Detail", it should have "Desired Access: Generic Write". And it should have "ShareMode: Read", which corresponds to FILE_SHARE_READ in the call to CreateFile. What it means is, "I, logwriter, permit others to read my file".
Now run your log-reading application ("logreader"), and do the same exercise.
The Detail should have "Desired Access: Generic Read". And it should have "ShareMode: Read, Write", which means, "I, logreader, permit others, including logwriter, to read and write to the log file".
Those are the most sensible values, I think, and they will prevent locking. Other combinations may be permissible. There is a table here.
Now, you haven't said what happens when it "does not seem to work in all cases". What to do next will really depend on the details. Hopefully the above will give you enough information to work out what is going wrong.
You won't get a lock conflict because the writing application is very unlikely to have locked the file. Doing what you suggest generally works without problems (it's what the UNIX tail -f command does) and those minor glitches that do occur can be ignored. I've written a couple of log monitoring apps in te past that worked like this, with no problems.
Try using FileSystemWatcher to get events when a file is updated.
A more delphi friendly link
Quite apart from getting the file sharing to work right which may be impossible depending on what the other program requests, some programs will close the file between accesses.
I have had success in the past with my program waiting for the file to become available, then quickly opening it, grabbing the needed data and closing it. At least in DOS an attempt to access a locked file caused a few retries, and I bumped up this setting, so that if the other program tried for the file while I had it they would simply be delayed and never see an error.
I was even able to update the file (I made sure NOT to close it in between!) without the other program ever knowing a thing.
Ugly as sin but we couldn't change the other program so it was the only way to get the job done. It was deployed in-house for years, I never heard a peep from the users of that system. It finally went away when the machinery the other program controlled was retired.
XpoLog will do the trick without changing your env or code, XpoLog log monitor
Avar is right - you are at the mercy of the writing program here. If they are locking the file, then there are a couple of things you can do:
1 - Check for a change in the "last modified" date time - if that changes, then you know something has happened.
2 - If the mod datetime did change, then (depending on the size of the file) it might be good enough to create a copy of the file and check that.
we use "Tail for win32",
i know its not delphi but it might be useful
http://tailforwin32.sourceforge.net/