Topic       : The ATARI Compendium
Author      : Scott Sanders / JAY Software
Version     : 1.25 (20/6/2003)
Subject     : Documentation
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Index Size  : 32614
HCP-Version : 6
Compiled on : Atari
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View Ref-FileFopen()
Fwrite()
Fread()
Flock()                                                              GEMDOS

Syntax

LONG Flock( handle, mode, start, length )
WORD handle,mode;
LONG start,length;

Function      Flock() sets or removes a lock on a portion of a file which
              prevents other processes from accessing it.

Opcode        92 ($5C)

Availability  Only present when '_FLK' cookie exists.

Parameters    handle specifies the GEMDOS handle of the file. mode is
              FLK_LOCK (0) to create a lock and FLK_UNLOCK (1) to remove
              it. start specifies the byte offset from the beginning of
              the file which indicates where the lock starts. length
              specifies the length of the lock in bytes.

Binding       move.l   length,-(sp)
              move.l   start,-(sp)
              move.w   mode,-(sp)
              move.w   handle,-(sp)
              trap     #1
              lea      12(sp),sp

Return Value  Flock() returns E_OK (0) if the call was successful, ELOCKED
              (-58) if an overlapping section of the file was already
              locked, ENSLOCK (-59) if a matching lock was not found for
              removal, or another GEMDOS error code as appropriate.

Comments      To remove a lock, you must specify identical start and
              length parameters as you originally set. MiNT allows locks to
              be set on devices by locking their entry in 'U:\DEV\' as
              shown in the example below:

              handle = Fopen( "U:\DEV\MODEM1", 3 );
              if( handle < 0)
                 return ERR_CODE;  /* Unable to open. */

              retcode = Flock( (WORD)handle, 0, 0, 0 );  /* Lock */
              if( retcode != E_OK )
                 return FILE_IN_USE; /* File is already locked */

               /*
                * Now do device input/output.
                */

              Flock( (WORD)handle, 1, 0, 0 );  /* Unlock */
              Fclose( (WORD)handle );

See Also      Fopen(), Fwrite(), Fread()