1. Re: file/data sharing
At 03:51 PM 6/7/98 -0500, Terry Constantwrote:
>Irv,
>I am new to Euphoria. But if it continues to prove out as it has been, I
>intend to use on a networked system of a client in which I will be using
>it with shared data. So, I am interested.
>--
>Terry Constant
>--
Well, here's what we need to get started:
From the shareware version of
** Programmer's Technical Reference for MSDOS and the IBM PC **
by Dave Williams
Function 6Ch Extended Open/Create DOS 4.0+ (US)
Combines functions available with Open, Create,
CreateNew, and Commit File
entry AH 6Ch
AL 00h reserved [which means there might be other
subfunctions?]
BX mode format 0WF0 0000 ISSS 0AAA
AAA is access code (read, write,
read/write)
SSS is sharing mode
I 0 pass handle to child
1 no inherit [interesting!]
F 0 use int 24h for errors
1 disable int 24h for all
I/O on this handle; use
own error routine
W 0 no commit
1 auto commit on all writes
CX create attribute
bits 0 read only
1 hidden
2 system
3 volume label
4 reserved
5 archive
6-15 reserved
DH 00h (reserved)
DL action if file exists/does not exists
bits 0-3 action if file exists
0000 fail
0001 open
0010 replace/open
4-7 action if file does not exist
0000 fail
0001 create
DS:SI pointer to ASCIIZ file name
return CF set on error
AX error code (unknown)
clear
AX file handle
CX action taken
01h file opened
02h file created/opened
03h file replaced/opened
note When APPEND is installed, if DX=xx1x it looks only in current
directory, if DX=xx0x it will search the full append path.
DX is called the open flag and gives what action to take if
the file exists or does not exist.
Function 5Ch Lock/Unlock File Access (DOS 3.0+)
entry AH 5Ch
AL 00h to lock file region
01h to unlock file region
BX file handle
CX:DX 4-byte starting offset from beginning of file of region
to lock
SI:DI 4-byte integer, high/low size of region to lock
(in bytes)
return CF clear successful
set AX error code (01h, 06h, 21h, 24h)
note 1) Unlock all files before exiting or undefined results may occur.
Programs using file locking should trap int 23h (Control-C
Handler Address) and int 24h (Critical Error Handler Address)
and unlock files before returning to the caller.
2) Programs spawned with EXEC inherit all the parent's file
handles but not the file locks.
3) This call is explicitly supported in the OS/2 1.x DOS
Compatibility Box.
4) You may lock an entire file, any part of a file, or several
parts of the same file. For example, it would be more
efficient to lock an area in a database containing a single
record than to lock the entire file. If two adjacent sections
of a file are locked separately, they must be unlocked
separately - you cannot change the lock pointers and use a
single unlock call.
5) You should lock only as much of a file as you need and keep
the lock only for as long as necessary. Should a file need to
be shared and updated often, continual locking and unlocking
can slow file access detectably.
6) This call returns error 01h if SHARE is not loaded.
7) Locked files must be unlocked before the program terminates,
or the result is undefined.
8) A transaction-oriented algorithm for using locking is
recommended. In effect, assert lock, read data, change data,
remove lock. An application should release its lock when a
transaction is complete.
9) Locking past end-of-file does not cause an error.
10) Locking a portion of a file with fn 5Ch denies all other
processes both read and write access to the locked region.
11) For PC-MOS/386 native mode, use ECX and EDX instead of CX:DX.
Irv
