Record/Row Locking

..\sdk\sql.embedded\tutorials\eSQL_Tutorial3.pc

Now we will explore row/record locks using the c-treeACE SQL ESQL - Embedded SQL Interface

The functionality for this tutorial focuses on inserting/adding rows/records, then updating a single row/record in the customer master table under locking control. The application will pause after a LOCK is placed on a row/record. Another instance of this application should then be launched, which will block, waiting on the lock held by the first instance. Pressing the <Enter> key will enable the first instance to proceed. This will result in removing the lock thereby allowing the second instance to continue execution. Launching two processes provides a visual demonstration of the effects of locking and a basis for experimentation on your own.

Like all other examples in the c-tree tutorial series, this tutorial simplifies the creation and use of a database into four simple steps: Initialize(), Define(), Manage(), and you’re Done() !

Tutorial #3: Locking

Here we demonstrate the enforcement of data integrity by introducing record/row "locking".

• Initialize() - Connects to the c-treeACE Database Engine.
• Define() - Defines and creates a "customer master" (custmast) table/file.
• Manage() - Adds a few rows/records; Reads the rows/records back from the database; displays the column/field content. Then demonstrates an update operation under locking control, and a scenario that shows a locking conflict.
• Done() - Disconnects from c-treeACE Database Engine.

Note our simple mainline:

/*

 * main()

 *

 * The main() function implements the concept of "init, define, manage

 * and you're done..."

 */

int main(int argc, char* argv[])

{

   Initialize();

   Define();

   Manage();

   Done();

   os_printf(DH_STRING_LITERAL("\nPress <ENTER> key to exit . . .\n"));

   getchar();

   return(0);

}

We suggest opening the source code with your own editor.

Continue now to review these four steps.