[fpc-pascal] File region locking unde Linux

[Jonas Maebe]

On 03 May 2009, at 14:51, Jonas Maebe wrote:

> 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.

It's similar to http://bugs.freepascal.org/view.php?id=13363 : the  
kernel's off_t is 32 bit on 32 bit systems. It's defined as 64 bit in  
the Linux rtl for all platforms.


Jonas