locking.c

C标准库源代码

/***
*locking.c - file locking function
*
*       Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Defined the _locking() function - file locking and unlocking
*
*******************************************************************************/

#ifndef _MAC


#include <cruntime.h>
#include <oscalls.h>
#include <errno.h>
#include <sys\locking.h>
#include <io.h>
#include <stdlib.h>
#include <internal.h>
#include <msdos.h>
#include <mtdll.h>

/***
*int _locking(fh,lmode,nbytes) - file record locking function
*
*Purpose:
*       Locks or unlocks nbytes of a specified file
*
*       Multi-thread - Must lock/unlock the file handle to prevent
*       other threads from working on the file at the same time as us.
*       [NOTE: We do NOT release the lock during the 1 second delays
*       since some other thread could get in and do something to the
*       file.  The DOSFILELOCK call locks out other processes, not
*       threads, so there is no multi-thread deadlock at the DOS file
*       locking level.]
*
*Entry:
*       int fh -        file handle
*       int lmode -     locking mode:
*                           _LK_LOCK/_LK_RLCK -> lock, retry 10 times
*                           _LK_NBLCK/_LK_N_BRLCK -> lock, don't retry
*                           _LK_UNLCK -> unlock
*       long nbytes -   number of bytes to lock/unlock
*
*Exit:
*       returns 0 if successful
*       returns -1 and sets errno if unsuccessful
*
*Exceptions:
*
*******************************************************************************/

int __cdecl _locking (
        int fh,
        int lmode,
        long nbytes
        )
{
        ULONG dosretval;                /* o.s. return code */
        LONG lockoffset;
        int retry;                      /* retry count */

        /* validate file handle */
        if ( ((unsigned)fh >= (unsigned)_nhandle) ||
             !(_osfile(fh) & FOPEN) )
        {
                /* fh out of range */
                errno = EBADF;
                _doserrno = 0;  /* not an o.s. error */
                return -1;
        }

        _lock_fh(fh);                   /* acquire file handle lock */

        /* obtain current position in file by calling _lseek */
        /* Use _lseek_lk as we already own lock */
        lockoffset = _lseek_lk(fh, 0L, 1);
        if (lockoffset == -1) {
                _unlock_fh(fh);
                return -1;
        }


        /* set retry count based on mode */
        if (lmode == _LK_LOCK || lmode == _LK_RLCK)
                retry = 9;              /* retry 9 times */
        else
                retry = 0;              /* don't retry */

        /* ask o.s. to lock the file until success or retry count finished */
        /* note that the only error possible is a locking violation, since */
        /* an invalid handle would have already failed above */
        for (;;) {

                dosretval = 0;
                if (lmode == _LK_UNLCK) {
                    if ( !(UnlockFile((HANDLE)_get_osfhandle(fh),
                                      lockoffset,
                                      0L,
                                      nbytes,
                                      0L))
                       )
                        dosretval = GetLastError();

                } else {
                    if ( !(LockFile((HANDLE)_get_osfhandle(fh),
                                    lockoffset,
                                    0L,
                                    nbytes,
                                    0L))
                       )
                        dosretval = GetLastError();
                }

                if (retry <= 0 || dosretval == 0)
                        break;  /* exit loop on success or retry exhausted */

                Sleep(1000L);

                --retry;
        }

        _unlock_fh(fh);                 /* release the file handle lock */

        if (dosretval != 0) {
                /* o.s. error occurred -- file was already locked; if a
                   blocking call, then return EDEADLOCK, otherwise map
                   error normally */
                if (lmode == _LK_LOCK || lmode == _LK_RLCK) {
                        errno = EDEADLOCK;
                        _doserrno = dosretval;
                }
                else {
                        _dosmaperr(dosretval);
                }
                return -1;
        }
        else
                return 0;
}


#else  /* _MAC */


#include <cruntime.h>
#include <errno.h>
#include <sys\locking.h>
#include <io.h>
#include <stdlib.h>
#include <internal.h>
#include <memory.h>
#include <msdos.h>
#include <macos\files.h>
#include <macos\errors.h>

#include <stdio.h>

/***
*int _locking(fh,lmode,nbytes) - file record locking function
*
*Purpose:
*       Locks or unlocks nbytes of a specified file
*
*
*Entry:
*       int fh -        file handle
*       int lmode -     locking mode:
*                           _LK_LOCK/_LK_RLCK -> not supported
*                           _LK_NBLCK/_LK_N_BRLCK -> lock, don't retry
*                           _LK_UNLCK -> unlock
*       long nbytes -   number of bytes to lock/unlock
*
*Exit:
*       returns 0 if successful
*       returns -1 and sets errno if unsuccessful
*
*Exceptions:
*
*******************************************************************************/

int __cdecl _locking (
        int fh,
        int lmode,
        long nbytes
        )
{
        ParamBlockRec param;
        OSErr osErr;

        /* validate file handle */
        if ((unsigned)fh >= (unsigned)_nfile || !(_osfile[fh] & FOPEN)) {
                /* fh out of range */
                errno = EBADF;
                _macerrno = 0;
                return -1;
        }

        memset(&param, 0, sizeof(ParamBlockRec));
        param.ioParam.ioRefNum = _osfhnd[fh];
        param.ioParam.ioReqCount =      nbytes;
        param.ioParam.ioPosMode = fsAtMark;
        param.ioParam.ioPosOffset = 0;

        switch (lmode)
        {
                case LK_UNLCK:
                        if (_osfile[fh] & FLOCK)
                        {
                                osErr = PBUnlockRangeSync(&param);
                        }
                        else
                        {
                                errno = EACCES;
                                return -1;
                        }
                        break;

                case _LK_NBLCK:
                case  LK_NBRLCK:
                        osErr = PBLockRangeSync(&param);

                        /* If this fh hasn't been locked before test the    */
                        /* lock. This test is needed because the Mac will   */
                        /* not lock local files but it will not return an   */
                        /* error                                            */
                        if (osErr == 0  && !(_osfile[fh] & FLOCK))
                        {
                            /* If lock took this should error */
                            if (PBLockRangeSync(&param))
                                {
                                        _osfile[fh] |= FLOCK;
                                }
                                else
                                {
                                        errno = EINVAL;
                                        return -1;
                                }
                        }
                        break;

                default:
                        errno = EINVAL;
                        return -1;
        }

        if (osErr)
        {
                _dosmaperr(osErr);
                return -1;
        }
        return 0;
}


#endif  /* _MAC */