1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Transactional Cursors</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> 10 <link rel="up" href="usingtxns.html" title="Chapter��3.��Transaction Basics" /> 11 <link rel="prev" href="nestedtxn.html" title="Nested Transactions" /> 12 <link rel="next" href="txnindices.html" title="Secondary Indices with Transaction Applications" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Transactional Cursors</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��3.��Transaction Basics</th> 23 <td width="20%" align="right">��<a accesskey="n" href="txnindices.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="sect1" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title" style="clear: both"><a id="txncursor"></a>Transactional Cursors</h2> 33 </div> 34 </div> 35 </div> 36 <p> 37 You can transaction-protect your cursor operations by 38 specifying a transaction handle at the time that you create 39 your cursor. Beyond that, you do not ever 40 provide a transaction handle directly to a cursor method. 41 </p> 42 <p> 43 Note that if you transaction-protect a cursor, then you must 44 make sure that the cursor is closed before you either commit or 45 abort the transaction. For example: 46 </p> 47 <pre class="programlisting">#include <stdio.h> 48#include <stdlib.h> 49 50#include "db.h" 51 52int 53main(void) 54{ 55 DBT key, data; 56 DBC *cursorp; 57 DB_TXN *txn = NULL; 58 int ret, c_ret; 59 char *replacementString = "new string"; 60 61 ... 62 /* environment and db handle creation omitted */ 63 ... 64 65 /* Get the txn handle */ 66 txn = NULL; 67 ret = envp->txn_begin(envp, NULL, &txn, 0); 68 if (ret != 0) { 69 envp->err(envp, ret, "Transaction begin failed."); 70 goto err; 71 } 72 73 /* Get the cursor, supply the txn handle at that time */ 74 ret = dbp->cursor(dbp, txn, &cursorp, 0); 75 if (ret != 0) { 76 envp->err(envp, ret, "Cursor open failed."); 77 txn->abort(txn); 78 goto err; 79 } 80 81 /* 82 * Now use the cursor. Note that we do not supply any txn handles to these 83 * methods. 84 */ 85 /* Prepare the DBTs */ 86 memset(&key, 0, sizeof(DBT)); 87 memset(&data, 0, sizeof(DBT)); 88 while (cursor->get(&key, &data, DB_NEXT) == 0) { 89 data->data = (void *)replacementString; 90 data->size = (strlen(replacementString) + 1) * sizeof(char); 91 c_ret = cursor->put(cursor, &key, &data, DB_CURRENT); 92 if (c_ret != 0) { 93 /* abort the transaction and goto error */ 94 envp->err(envp, ret, "Cursor put failed."); 95 cursorp->close(cursorp); 96 cursorp = NULL; 97 txn->abort(txn); 98 goto err; 99 } 100 } 101 102 /* 103 * Commit the transaction. Note that the transaction handle 104 * can no longer be used. 105 */ 106 ret = cursorp->close(cursorp); 107 if (ret != 0) { 108 envp->err(envp, ret, "Cursor close failed."); 109 txn->abort(txn); 110 goto err; 111 } 112 ret = txn->commit(txn, 0); 113 if (ret != 0) { 114 envp->err(envp, ret, "Transaction commit failed."); 115 goto err; 116 } 117 118err: 119 /* Close the cursor (if the handle is not NULL) 120 * and perform whatever other cleanup is required */ 121 122 /* Close the database */ 123 124 /* Close the environment */ 125 126 ... 127 128 if (c_ret != 0) 129 ret = c_ret; 130 131 return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE); 132} </pre> 133 </div> 134 <div class="navfooter"> 135 <hr /> 136 <table width="100%" summary="Navigation footer"> 137 <tr> 138 <td width="40%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a>��</td> 139 <td width="20%" align="center"> 140 <a accesskey="u" href="usingtxns.html">Up</a> 141 </td> 142 <td width="40%" align="right">��<a accesskey="n" href="txnindices.html">Next</a></td> 143 </tr> 144 <tr> 145 <td width="40%" align="left" valign="top">Nested Transactions��</td> 146 <td width="20%" align="center"> 147 <a accesskey="h" href="index.html">Home</a> 148 </td> 149 <td width="40%" align="right" valign="top">��Secondary Indices with Transaction Applications</td> 150 </tr> 151 </table> 152 </div> 153 </body> 154</html> 155