os_flock.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997-2005
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: os_flock.c,v 1.6 2005/06/16 20:23:28 bostic Exp $
 */

#include "db_config.h"

#include "db_int.h"

/*
 * __os_fdlock --
 *      Acquire/release a lock on a byte in a file.
 *
 * PUBLIC: int __os_fdlock __P((DB_ENV *, DB_FH *, off_t, int, int));
 */
int
__os_fdlock(dbenv, fhp, offset, acquire, nowait)
        DB_ENV *dbenv;
        DB_FH *fhp;
        int acquire, nowait;
        off_t offset;
{
        int ret;
        DWORD low, high;
        OVERLAPPED over;

        DB_ASSERT(F_ISSET(fhp, DB_FH_OPENED) &&
            fhp->handle != INVALID_HANDLE_VALUE);

        /*
         * Windows file locking interferes with read/write operations, so we
         * map the ranges to an area past the end of the file.
         */
        DB_ASSERT(offset < (u_int64_t)INT64_MAX);
        offset = UINT64_MAX - offset;
        low = (DWORD)offset;
        high = (DWORD)(offset >> 32);

        if (acquire) {
                if (nowait)
                        RETRY_CHK_EINTR_ONLY(
                            !LockFile(fhp->handle, low, high, 1, 0), ret);
                else if (__os_is_winnt()) {
                        memset(&over, 0, sizeof over);
                        over.Offset = low;
                        over.OffsetHigh = high;
                        RETRY_CHK_EINTR_ONLY(
                            !LockFileEx(fhp->handle, LOCKFILE_EXCLUSIVE_LOCK,
                            0, 1, 0, &over),
                            ret);
                } else {
                        /* Windows 9x/ME doesn't support a blocking call. */
                        for (;;) {
                                RETRY_CHK_EINTR_ONLY(
                                    !LockFile(fhp->handle, low, high, 1, 0),
                                    ret);
                                if (ret != EAGAIN)
                                        break;
                                __os_sleep(dbenv, 1, 0);
                        }
                }
        } else
                RETRY_CHK_EINTR_ONLY(
                    !UnlockFile(fhp->handle, low, high, 1, 0), ret);

        return (ret);
}

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