206 lines
7 KiB
C
206 lines
7 KiB
C
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/***
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*locking.c - file locking function
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*
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* Copyright (c) 1989-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Defined the _locking() function - file locking and unlocking
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*
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*Revision History:
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* 06-09-89 PHG Module created, based on asm version
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* 08-10-89 JCR Changed DOS32FILELOCKS to DOS32SETFILELOCKS
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* 03-12-90 GJF Made calling type _CALLTYPE2 (for now), added #include
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* <cruntime.h> and fixed the copyright. Also, cleaned up
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* the formatting a bit.
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* 04-03-90 GJF Now _CALLTYPE1.
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* 07-24-90 SBM Removed '32' from API names
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* 08-14-90 SBM Compiles cleanly with -W3
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* 09-28-90 GJF New-style function declarator.
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* 12-04-90 GJF Appended Win32 version onto the source with #ifdef-s.
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* It is enough different that there is little point in
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* trying to more closely merge the two versions.
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* 12-04-90 SRW Changed to include <oscalls.h> instead of <doscalls.h>
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* 12-06-90 SRW Changed to use _osfile and _osfhnd instead of _osfinfo
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* 01-16-91 GJF ANSI naming.
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* 02-07-91 SRW Changed to call _get_osfhandle [_WIN32_]
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* 12-05-91 GJF Fixed usage of [Un]LockFile APIs [_WIN32_].
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* 02-13-92 GJF Replaced _nfile by _nhandle for Win32.
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* 05-06-92 SRW WIN32 LockFile API changed. [_WIN32_].
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* 04-06-93 SKS Replace _CRTAPI* with __cdecl
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* 09-06-94 CFW Remove Cruiser support.
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* 12-03-94 SKS Clean up OS/2 references
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* 01-04-95 GJF _WIN32_ -> _WIN32
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* 02-15-95 GJF Appended Mac version of source file (somewhat cleaned
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* up), with appropriate #ifdef-s.
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* 06-27-95 GJF Added check that the file handle is open.
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* 07-08-96 GJF Replaced defined(_WIN32) with !defined(_MAC), and
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* defined(_M_M68K) || defined(_M_MPPC) with
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* defined(_MAC). Also, detab-ed and cleaned up the
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* format a bit.
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* 12-19-97 GJF Exception-safe locking.
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* 05-17-99 PML Remove all Macintosh support.
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*
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*******************************************************************************/
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#include <cruntime.h>
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#include <oscalls.h>
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#include <errno.h>
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#include <sys\locking.h>
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#include <io.h>
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#include <stdlib.h>
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#include <internal.h>
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#include <msdos.h>
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#include <mtdll.h>
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#ifdef _MT
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static int __cdecl _locking_lk(int, int, long);
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#endif
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/***
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*int _locking(fh,lmode,nbytes) - file record locking function
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*
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*Purpose:
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* Locks or unlocks nbytes of a specified file
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*
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* Multi-thread - Must lock/unlock the file handle to prevent
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* other threads from working on the file at the same time as us.
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* [NOTE: We do NOT release the lock during the 1 second delays
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* since some other thread could get in and do something to the
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* file. The DOSFILELOCK call locks out other processes, not
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* threads, so there is no multi-thread deadlock at the DOS file
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* locking level.]
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*
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*Entry:
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* int fh - file handle
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* int lmode - locking mode:
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* _LK_LOCK/_LK_RLCK -> lock, retry 10 times
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* _LK_NBLCK/_LK_N_BRLCK -> lock, don't retry
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* _LK_UNLCK -> unlock
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* long nbytes - number of bytes to lock/unlock
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*
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*Exit:
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* returns 0 if successful
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* returns -1 and sets errno if unsuccessful
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*
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*Exceptions:
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*
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*******************************************************************************/
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int __cdecl _locking (
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int fh,
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int lmode,
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long nbytes
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)
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{
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#ifdef _MT
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int retval;
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#else
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ULONG dosretval; /* o.s. return code */
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LONG lockoffset;
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int retry; /* retry count */
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#endif
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/* validate file handle */
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if ( ((unsigned)fh >= (unsigned)_nhandle) ||
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!(_osfile(fh) & FOPEN) )
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{
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/* fh out of range */
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errno = EBADF;
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_doserrno = 0; /* not an o.s. error */
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return -1;
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}
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#ifdef _MT
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_lock_fh(fh); /* acquire file handle lock */
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__try {
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if ( _osfile(fh) & FOPEN )
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retval = _locking_lk(fh, lmode, nbytes);
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else {
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errno = EBADF;
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_doserrno = 0; /* not an o.s. error */
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retval = -1;
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}
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}
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__finally {
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_unlock_fh(fh);
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}
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return retval;
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}
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static int __cdecl _locking_lk (
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int fh,
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int lmode,
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long nbytes
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)
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{
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ULONG dosretval; /* o.s. return code */
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LONG lockoffset;
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int retry; /* retry count */
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#endif /* _MT */
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/* obtain current position in file by calling _lseek */
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/* Use _lseek_lk as we already own lock */
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lockoffset = _lseek_lk(fh, 0L, 1);
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if (lockoffset == -1)
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return -1;
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/* set retry count based on mode */
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if (lmode == _LK_LOCK || lmode == _LK_RLCK)
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retry = 9; /* retry 9 times */
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else
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retry = 0; /* don't retry */
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/* ask o.s. to lock the file until success or retry count finished */
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/* note that the only error possible is a locking violation, since */
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/* an invalid handle would have already failed above */
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for (;;) {
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dosretval = 0;
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if (lmode == _LK_UNLCK) {
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if ( !(UnlockFile((HANDLE)_get_osfhandle(fh),
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lockoffset,
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0L,
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nbytes,
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0L))
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)
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dosretval = GetLastError();
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} else {
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if ( !(LockFile((HANDLE)_get_osfhandle(fh),
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lockoffset,
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0L,
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nbytes,
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0L))
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)
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dosretval = GetLastError();
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}
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if (retry <= 0 || dosretval == 0)
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break; /* exit loop on success or retry exhausted */
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Sleep(1000L);
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--retry;
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}
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if (dosretval != 0) {
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/* o.s. error occurred -- file was already locked; if a
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blocking call, then return EDEADLOCK, otherwise map
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error normally */
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if (lmode == _LK_LOCK || lmode == _LK_RLCK) {
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errno = EDEADLOCK;
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_doserrno = dosretval;
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}
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else {
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_dosmaperr(dosretval);
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}
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return -1;
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}
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else
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return 0;
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}
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