OpenTransactionList


1   /**
2    * com.mckoi.database.OpenTransactionList  26 Nov 2000
3    *
4    * Mckoi SQL Database ( http://www.mckoi.com/database )
5    * Copyright (C) 2000, 2001, 2002  Diehl and Associates, Inc.
6    *
7    * This program is free software; you can redistribute it and/or
8    * modify it under the terms of the GNU General Public License
9    * Version 2 as published by the Free Software Foundation.
10   *
11   * This program is distributed in the hope that it will be useful,
12   * but WITHOUT ANY WARRANTY; without even the implied warranty of
13   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14   * GNU General Public License Version 2 for more details.
15   *
16   * You should have received a copy of the GNU General Public License
17   * Version 2 along with this program; if not, write to the Free Software
18   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
19   *
20   * Change Log:
21   * 
22   * 
23   */
24  
25  package com.mckoi.database;
26  
27  import java.util.ArrayList  ;
28  import com.mckoi.debug.Lvl;
29  
30  /**
31   * The list of all currently open transactions.  This is a thread safe
32   * object that is shared between a TableDataConglomerate and its children
33   * MasterDataTableSource objects.  It is used for maintaining a list of
34   * transactions that are currently open in the system.  It also provides
35   * various utility methods around the list.
36   * <p>
37   * This class is thread safe and can safely be accessed by multiple threads.
38   * This is so threads accessing table source information as well as
39   * conglomerate 'commit' stages can safely access this object.
40   *
41   * @author Tobias Downer
42   */
43  
44  final class OpenTransactionList {
45  
46    /**
47     * True to enable transaction tracking.
48     */
49    private static final boolean TRACKING = false;
50    
51    /**
52     * The system that this transaction list is part of.
53     */
54    private TransactionSystem system;
55  
56    /**
57     * The list of open transactions.
58     * (Transaction).
59     */
60    private ArrayList   open_transactions;
61  
62    /**
63     * A list of Error objects created when the transaction is added to the open
64     * transactions list.
65     */
66    private ArrayList   open_transaction_stacks;
67    
68    /**
69     * The minimum commit id of the current list.
70     */
71    private long minimum_commit_id;
72  
73    /**
74     * The maximum commit id of the current list.
75     */
76    private long maximum_commit_id;
77  
78    /**
79     * Creates the list.
80     */
81    OpenTransactionList(TransactionSystem system) {
82      this.system = system;
83      open_transactions = new ArrayList  ();
84      if (TRACKING) {
85        open_transaction_stacks = new ArrayList  ();
86      }
87      minimum_commit_id = Long.MAX_VALUE;
88      maximum_commit_id = 0;
89    }
90  
91    /**
92     * Adds a new open transaction to the list.  Transactions must be added
93     * in order of commit_id.
94     */
95    synchronized void addTransaction(Transaction transaction) {
96      long current_commit_id = transaction.getCommitID();
97      if (current_commit_id >= maximum_commit_id) {
98        open_transactions.add(transaction);
99        if (TRACKING) {
100         open_transaction_stacks.add(new Error  ());
101       }
102       system.stats().increment("OpenTransactionList.count");
103       maximum_commit_id = current_commit_id;
104     }
105     else {
106       throw new Error  (
107                    "Added a transaction with a lower than maximum commit_id");
108     }
109   }
110 
111   /**
112    * Removes an open transaction from the list.
113    */
114   synchronized void removeTransaction(Transaction transaction) {
115     
116     int size = open_transactions.size();
117     int i = open_transactions.indexOf(transaction);
118     if (i == 0) {
119       // First in list.
120       if (i == size - 1) {
121         // And last.
122         minimum_commit_id = Integer.MAX_VALUE;
123         maximum_commit_id = 0;
124       }
125       else {
126         minimum_commit_id =
127                    ((Transaction) open_transactions.get(i + 1)).getCommitID();
128       }
129     }
130     else if (i == open_transactions.size() - 1) {
131       // Last in list.
132       maximum_commit_id =
133                    ((Transaction) open_transactions.get(i - 1)).getCommitID();
134     }
135     else if (i == -1) {
136       throw new Error  ("Unable to find transaction in the list.");
137     }
138     open_transactions.remove(i);
139     if (TRACKING) {
140       open_transaction_stacks.remove(i);
141     }
142     system.stats().decrement("OpenTransactionList.count");
143 
144     if (TRACKING) {
145       system.Debug().write(Lvl.MESSAGE, this, "Stacks:");
146       for (int n = 0; n < open_transaction_stacks.size(); ++n) {
147         system.Debug().writeException(Lvl.MESSAGE,
148                                       (Error  ) open_transaction_stacks.get(n));
149       }
150     }
151 
152   }
153 
154   /**
155    * Returns the number of transactions that are open on the conglomerate.
156    */
157   synchronized int count() {
158     return open_transactions.size();
159   }
160 
161   /**
162    * Returns the minimum commit id not including the given transaction object.
163    * Returns Long.MAX_VALUE if there are no open transactions in the list
164    * (not including the given transaction).
165    */
166   synchronized long minimumCommitID(Transaction transaction) {
167 
168     long minimum_commit_id = Long.MAX_VALUE;
169     if (open_transactions.size() > 0) {
170       // If the bottom transaction is this transaction, then go to the
171       // next up from the bottom (we don't count this transaction as the
172       // minimum commit_id).
173       Transaction test_transaction = (Transaction)open_transactions.get(0);
174       if (test_transaction != transaction) {
175         minimum_commit_id = test_transaction.getCommitID();
176       }
177       else if (open_transactions.size() > 1) {
178         minimum_commit_id =
179                         ((Transaction) open_transactions.get(1)).getCommitID();
180       }
181     }
182 
183     return minimum_commit_id;
184 
185   }
186 
187   public synchronized String   toString() {
188     StringBuffer   buf = new StringBuffer  ();
189     buf.append("[ OpenTransactionList: ");
190     for (int i = 0; i < open_transactions.size(); ++i) {
191       Transaction t = (Transaction) open_transactions.get(i);
192       buf.append(t.getCommitID());
193       buf.append(", ");
194     }
195     buf.append(" ]");
196     return new String  (buf);
197   }
198 
199 }
200
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