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

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

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

static const char szTblName[] = "cust";
static const char szTblType[] = szDBASE;

//=====================================================================
//  Function:
//          RecLock();
//
//  Description:
//          This example shows how to do record locking.  The
//          example will simulate multi-user access by creating multiple
//          sessions. The example will show both working and failing locks.
//=====================================================================
void
RecLock (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("*** Record 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;
    }

    // Aquire a new session. This is 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 buffers.
    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 = DbiCloseCursor(&hCur2);
        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");

    Screen("    Session #2 is getting and locking the first record...");
    rslt = DbiSetToBegin(hCur2);
    ChkRslt(rslt, "SetToBegin");
    rslt = DbiGetNextRecord(hCur2, dbiWRITELOCK, pRecBuf2, NULL);
    ChkRslt(rslt, "GetRecord");

    // Set the current session to session #1.
    rslt = DbiSetCurrSession(hSession1);
    ChkRslt(rslt, "SetCurrSession");

    Screen("\r\n    Session #1 is getting the first record without"
           " locking it...");
    rslt = DbiSetToBegin(hCur1);
    ChkRslt(rslt, "SetToBegin");
    rslt = DbiGetNextRecord(hCur1, dbiNOLOCK, pRecBuf1, NULL);
    ChkRslt(rslt, "GetRecord");

    // Attempt to modify the record in session #1 - get an error as
    //   session #2 has the record locked.
    Screen("    Session #1 is modifying the record...");
    Screen("        Error Expected - record is locked...");
    rslt = DbiModifyRecord(hCur1, pRecBuf1, TRUE);
    ChkRslt(rslt, "GetRecord");

    // Switch the current session to session #2.
    rslt = DbiSetCurrSession(hSession2);
    ChkRslt(rslt, "SetCurrSession");

    // Modify the record in session #2. Session #2 locked the record,
    //   so it will succeed this time. Note that the lock is released
    //   after the record is modified. 
    Screen("\r\n    Session #2 is modifying the record...");
    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 %s table in session #2...", szTblName);
    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");

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

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