[fpc-pascal] File region locking unde Linux

[Jonas Maebe]

On 03 May 2009, at 14:09, ajv wrote:

> With Region Do                         Begin
>    l_type  := F_WRLCK; l_whence := SEEK_SET;
>    l_start := 10;      l_len    := 20
> End;
> If FpFcntl (F, F_SETLK, Region) = -1 Then
>    WriteLn ('unable to apply writelock');   //  <-- OK
> Sleep (20000);                              // Sleep 20 Sec
> FpClose (F);
> End.
> --------------------------------------------------------------------------------------
> Then within 20 seconds i start test to obtain a readlock on 80.
> This fails. Why? What am I doing wrong?

Your test works fine under Solaris. It's a bug somewhere in the FPC  
Linux units. strace shows this for your first program:

fcntl(3, F_SETLK, {type=F_WRLCK, whence=SEEK_SET, start=10, len=0}) = 0

As you can see, "len=0" is passed to the system call (instead of  
len=20), so it locks the entire file. That's the reason why the other  
program is unable to lock anything else.


Jonas