TeslaRel410/BORLAND/BDE/EXAMPLES/SNIPIT/TBLLOCK.C

// BDE - (C) Copyright 1995 by Borland International

// tbllock.c
#include "snipit.h"

static const char szTblName[] = "customer";
static const char szTblType[] = szPARADOX;

//=====================================================================
//  Function:
//          TblLock();
//
//  Description:
//          This example shows how to lock a table.  The
//          example will simulate multi-user access by opening a table from
//          multiple sessions. The example will show both working and
//          failing locks.
//=====================================================================
void
TblLock (void)
{
    DBIResult   rslt;       // Value returned from IDAPI functions
    CURProps    TblProps;   // Properties of the table.  Used to determine
                            // the size of the record.

    hDBIDb      hDb1;       // Handle to the first database
    hDBICur     hCur1;      // Handle to the first table
    hDBISes     hSession1;  // Handle to the first session
    pBYTE       pRecBuf1;   // Pointer to the record buffer

    hDBIDb      hDb2;       // Handle to the second database
    hDBICur     hCur2;      // Handle to the second table
    hDBISes     hSession2;  // Handle to the second session
    pBYTE       pRecBuf2;   // Pointer to the record buffer

    Screen("*** Table Locking Example ***\r\n");

    BREAK_IN_DEBUGGER();

    Screen("    Initializing IDAPI...\r\n");
    if (InitAndConnect(&hDb1) != DBIERR_NONE)
    {                                       
        Screen("\r\n*** End of Example ***");
        return;
    }

    // Acquire a session handle.  Initializing IDAPI opens a session.
    Screen("    Acquiring the current session's handle...");
    rslt = DbiGetCurrSession(&hSession1);
    ChkRslt(rslt, "GetCurrSession");

    Screen("    Setting the database directory in session #1...");
    rslt = DbiSetDirectory(hDb1, (pCHAR) szTblDirectory);
    ChkRslt(rslt, "SetDirectory");

    Screen("    Opening the \"%s\" table in session #1...", szTblName);
    rslt = DbiOpenTable(hDb1, (pCHAR) szTblName, (pCHAR) szTblType,
                        NULL, NULL, NULL, dbiREADWRITE, dbiOPENSHARED,
                        xltFIELD, FALSE, NULL, &hCur1);
    if (ChkRslt(rslt, "OpenTable") != DBIERR_NONE)
    {
        CloseDbAndExit(&hDb1);
        Screen("\r\n*** End of Example ***");
        return;
    }

    Screen("    Place a write lock on the table in session #1...");
    rslt = DbiAcqTableLock(hCur1, dbiWRITELOCK);
    ChkRslt(rslt, "AcqTableLock");

    // Create a new session to simulate multi-user table access.
    Screen("\r\n    Opening session #2...");
    rslt = DbiStartSession("", &hSession2, NULL);
    ChkRslt(rslt, "StartSession");

    Screen("\r\n    Opening Standard database in session #2...");
    rslt = DbiOpenDatabase("", 0, dbiREADWRITE, dbiOPENSHARED,
                           NULL, NULL, NULL, NULL, &hDb2);
    if (ChkRslt(rslt, "OpenDatabase") != DBIERR_NONE)
    {
        rslt = DbiCloseCursor(&hCur1);
        ChkRslt(rslt, "CloseCursor");
        CloseDbAndExit(&hDb1);
        Screen("\r\n*** End of Example ***");
        return;
    }

    Screen("    Setting the database directory in session #2...");
    rslt = DbiSetDirectory(hDb2, (pCHAR) szTblDirectory);
    ChkRslt(rslt, "SetDirectory");

    Screen("    Opening the \"%s\" table in session #2...", szTblName);
    rslt = DbiOpenTable(hDb2, (pCHAR) szTblName, (pCHAR) szTblType,
                        NULL, NULL, NULL, dbiREADWRITE, dbiOPENSHARED,
                        xltFIELD, FALSE, NULL, &hCur2);
    if (ChkRslt(rslt, "OpenTable") != DBIERR_NONE)
    {
        rslt = DbiCloseCursor(&hCur1);
        ChkRslt(rslt, "CloseCursor");
        rslt = DbiCloseDatabase(&hDb2);
        ChkRslt(rslt, "CloseDatabase");
        CloseDbAndExit(&hDb1);
        Screen("\r\n*** End of Example ***");
        return;
    }

    // Create the record buffer.
    rslt = DbiGetCursorProps(hCur2, &TblProps);
    ChkRslt(rslt, "GetCursorProps");

    pRecBuf1 = (pBYTE) malloc(TblProps.iRecBufSize * sizeof(BYTE));
    pRecBuf2 = (pBYTE) malloc(TblProps.iRecBufSize * sizeof(BYTE));
    if ((!pRecBuf1) || (!pRecBuf2))
    {
        if (pRecBuf1) free(pRecBuf1);
        if (pRecBuf2) free(pRecBuf2);
        rslt = DbiCloseCursor(&hCur1);
        ChkRslt(rslt, "CloseCursor");
        rslt = DbiCloseDatabase(&hDb2);
        ChkRslt(rslt, "CloseDatabase");
        CloseDbAndExit(&hDb1);
        Screen("\r\n*** End of Example ***");
        return;
    }

    // Initialize the record buffer.
    rslt = DbiInitRecord(hCur2, pRecBuf2);
    ChkRslt(rslt, "InitRecord");

    // Go to the top of the table.
    rslt = DbiSetToBegin(hCur2);
    ChkRslt(rslt, "SetToBegin");

    Screen("    Session #2 is getting and locking the first record...");
    Screen("        Error expected - file is locked...");
    rslt = DbiGetNextRecord(hCur2, dbiWRITELOCK, pRecBuf2, NULL);
    ChkRslt(rslt, "GetRecord");

    Screen("\r\n    Session #2 is getting the first record without locking...");
    rslt = DbiGetNextRecord(hCur2, dbiNOLOCK, pRecBuf2, NULL);
    ChkRslt(rslt, "GetRecord");

    Screen("\r\n    Session #2 is attempting to modify the record...");
    Screen("        Error expected - file is locked...");
    rslt = DbiModifyRecord(hCur2, pRecBuf2, TRUE);
    ChkRslt(rslt, "ModifyRecord");

    // Clean up.
    free(pRecBuf1);
    free(pRecBuf2);

    rslt = DbiSetCurrSession(hSession2);
    ChkRslt(rslt, "SetCurrSession");

    Screen("\r\n    Close the cursor to the table in session #2...");
    rslt = DbiCloseCursor(&hCur2);
    ChkRslt(rslt, "CloseCursor");

    Screen("    Close the database handle in session #2...");
    rslt = DbiCloseDatabase(&hDb2);
    ChkRslt(rslt, "CloseDatabase");

    Screen("    Closing session #2...");
    rslt = DbiCloseSession(hSession2);
    ChkRslt(rslt, "CloseSession");

    rslt = DbiSetCurrSession(hSession1);
    ChkRslt(rslt, "SetCurrSession");

    rslt = DbiRelTableLock(hCur1, TRUE, dbiWRITELOCK);
    ChkRslt(rslt, "RelTableLock");

    Screen("\r\n    Close the cursor to the table in session #1...");
    rslt = DbiCloseCursor(&hCur1);
    ChkRslt(rslt, "CloseCursor");

    Screen("    Close the database and exit IDAPI...");
    CloseDbAndExit(&hDb1);
    
    Screen("\r\n*** End of Example ***");
}