Re: File/Record locking on Linux with GPC

According to Pismo:

Perl and C have Flock, and GPC should (does?) have a similar call [...]

I just have discovered the following C header for `flock' (see `man flock' under Linux; I hope that DJGPP provides an equivalent function):

int flock ( int fd, int operation )

The equivalent Pascal declaration is

Function FLock ( fd, operation: Integer ): Integer; C;

You can look up the values for `operation' from the C include file.

The remaining problem is how to get the file descriptor `fd' from a Pascal `file'. First, you can get a C-style `FILE' pointer from a Pascal file using the `GetFile' function (built-in in gpc-971001):

Function GetFile ( Const F: <file type> ): Pointer;

(With GPC before gpc-971001, say

Function GetFile ( Const F: <file type> ): Pointer; AsmName '_p_getfile';

to declare the function.)

Having that you can use the `filenum' function to get the file number:

int fileno ( FILE *stream );

or, in Pascal,

Function FileNo ( Stream: Pointer ): Integer; C;

With this declarations, the following should do what you wish:

Function GetFile ( Const F: <file type> ): Pointer; AsmName '_p_getfile';

Function FileNo ( Stream: Pointer ): Integer; C;

Const SharedLock = 1; (* From <sys/file.h> under Linux *) ExclusiveLock = 2; Unlock = 8;

Var Foo: File of Bar;

...

Flock ( FileNo ( GetFile ( Foo ) ), SharedLock );

Good luck,

Peter

Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski@uni-essen.de - http://home.pages.de/~peter.gerwinski/ [971005] maintainer GNU Pascal [971001] - http://home.pages.de/~gnu-pascal/ [971005]