Hi, I have many process wanting to write in a file. Each process is going to open the file as a writeonly (using Assignfile and rewrite or fpOpen with o_WrOnly). But there is a risk that two processes simultaneously trying to write a message in the file. I want to use fpflock to avoid this. Is it possible? What I done is something like this: AssignFile (OutputFile, FileName); fpflock (OutputFile, LOCK_EX); Rewrite (OutputFile); ... The description of fpFlock does not say anything about the default behavior of fpFlock (Is it blocking?). What I saw told me that it is not blocking. Is it the correct way of using fpFlock? _______________________________________________ fpc-devel maillist - http://lists.freepascal.org/mailman/listinfo/fpc-devel

flock in Linux (at least) is blocking by default unless passed with specific parameter. You can try also to create a mutex that only when removed you will access the procedure/function that try to write to the file, and the process that created the mutex is the only one that can write to that file. You of course remove it when you closed the file. Just an idea... Ido On Fri, May 2, 2008 at 5:35 AM, amir wrote: > Hi, > > I have many process wanting to write in a file. Each process is going to > open the file as a writeonly (using Assignfile and rewrite or fpOpen with > o_WrOnly). But there is a risk that two processes simultaneously trying to > write a message in the file. I want to use fpflock to avoid this. Is it > possible? What I done is something like this: > > AssignFile (OutputFile, FileName); > fpflock (OutputFile, LOCK_EX); > Rewrite (OutputFile); > ... > > The description of fpFlock does not say anything about the default > behavior of fpFlock (Is it blocking?). What I saw told me that it is not > blocking. > > Is it the correct way of using fpFlock? > > > _______________________________________________ > fpc-devel maillist - > http://lists.freepascal.org/mailman/listinfo/fpc-devel > >

So what wrong is with the following code? When running two instance of this program, *both* print "After Flock" and wait for an input? uses Unix; var InputFile: TextFile; begin AssignFile (InputFile, 'Lock.txt'); WriteLn ('Before Flock'); Flush (Output); Fpflock (InputFile, LOCK_SH); WriteLn ('After Flock'); Flush (Output); Reset (InputFile); ReadLn; CloseFile (InputFile); end. ik wrote: > flock in Linux (at least) is blocking by default unless passed with > specific parameter. > > You can try also to create a mutex that only when removed you will > access the procedure/function that try to write to the file, and the > process that created the mutex is the only one that can write to that > file. > You of course remove it when you closed the file. > > Just an idea... > > Ido > > On Fri, May 2, 2008 at 5:35 AM, amir wrote: > > > > Hi, > > > > I have many process wanting to write in a file. Each process is going to > > open the file as a writeonly (using Assignfile and rewrite or fpOpen with > > o_WrOnly). But there is a risk that two processes simultaneously trying to > > write a message in the file. I want to use fpflock to avoid this. Is it > > possible? What I done is something like this: > > > > AssignFile (OutputFile, FileName); > > fpflock (OutputFile, LOCK_EX); > > Rewrite (OutputFile); > > ... > > > > The description of fpFlock does not say anything about the default > > behavior of fpFlock (Is it blocking?). What I saw told me that it is not > > blocking. > > > > Is it the correct way of using fpFlock? > > > > > > _______________________________________________ > > fpc-devel maillist - > > http://lists.freepascal.org/mailman/listinfo/fpc-devel > > > > > > > > > > > _______________________________________________ fpc-devel maillist - http://lists.freepascal.org/mailman/listinfo/fpc-devel

You should use LOCK_EX instead (exclusive lock rather then shared lock). >From the man file (man 2 flock): LOCK_SH Place a shared lock. More than one process may hold a shared lock for a given file at a given time. LOCK_EX Place an exclusive lock. Only one process may hold an exclusive lock for a given file at a given time. LOCK_UN Remove an existing lock held by this process. Ido On Tue, May 6, 2008 at 9:38 AM, amir wrote: > So what wrong is with the following code? > When running two instance of this program, *both* print "After Flock" and > wait for an input? > > uses > Unix; > var > InputFile: TextFile; > > begin > AssignFile (InputFile, 'Lock.txt'); > WriteLn ('Before Flock'); > Flush (Output); > Fpflock (InputFile, LOCK_SH); > WriteLn ('After Flock'); > Flush (Output); > > Reset (InputFile); > ReadLn; > > CloseFile (InputFile); > > end. > > > > ik wrote: > > >> flock in Linux (at least) is blocking by default unless passed with >> specific parameter. >> >> You can try also to create a mutex that only when removed you will >> access the procedure/function that try to write to the file, and the >> process that created the mutex is the only one that can write to that >> file. >> You of course remove it when you closed the file. >> >> Just an idea... >> >> Ido >> >> On Fri, May 2, 2008 at 5:35 AM, amir wrote: >> >> >> >>> Hi, >>> >>> I have many process wanting to write in a file. Each process is going >>> > to > >>> open the file as a writeonly (using Assignfile and rewrite or fpOpen >>> > with > >>> o_WrOnly). But there is a risk that two processes simultaneously trying >>> > to > >>> write a message in the file. I want to use fpflock to avoid this. Is it >>> possible? What I done is something like this: >>> >>> AssignFile (OutputFile, FileName); >>> fpflock (OutputFile, LOCK_EX); >>> Rewrite (OutputFile); >>> ... >>> >>> The description of fpFlock does not say anything about the default >>> behavior of fpFlock (Is it blocking?). What I saw told me that it is not >>> blocking. >>> >>> Is it the correct way of using fpFlock? >>> >>> >>> _______________________________________________ >>> fpc-devel maillist - >>> http://lists.freepascal.org/mailman/listinfo/fpc-devel >>> >>> >>> >>> >> >> >> >> > _______________________________________________ > fpc-devel maillist - > http://lists.freepascal.org/mailman/listinfo/fpc-devel > >