DbEnvPool


1   /*-
2    * See the file LICENSE for redistribution information.
3    *
4    * Copyright (c) 2000,2006 Oracle.  All rights reserved.
5    *
6    * $Id: DbEnvPool.java,v 1.38 2006/10/30 21:14:15 bostic Exp $
7    */
8   
9   package com.sleepycat.je.dbi;
10  
11  import java.io.File  ;
12  import java.io.IOException  ;
13  import java.util.Hashtable  ;
14  import java.util.Map  ;
15  
16  import com.sleepycat.je.DatabaseException;
17  import com.sleepycat.je.EnvironmentConfig;
18  
19  /**
20   * Singleton collection of database environments.
21   */
22  public class DbEnvPool {
23      /* singleton instance. */
24      private static DbEnvPool pool = new DbEnvPool();
25  
26      /* 
27       * Collection of environment handles, mapped by canonical directory 
28       * name->EnvironmentImpl object.
29       */
30      private Map   envs;
31  
32      /**
33       * Enforce singleton behavior.
34       */
35      private DbEnvPool() {
36          envs = new Hashtable  ();
37      }
38  
39      /**
40       * Access the singleton instance.
41       */
42      public static DbEnvPool getInstance() {
43          return pool;
44      }
45  
46      /**
47       * If the environment is not open, open it.
48       */
49      public EnvironmentImplInfo getEnvironment(File   envHome,
50                                                 EnvironmentConfig config ) 
51          throws DatabaseException {
52  
53          return getEnvironment(envHome, config, true);
54      }
55  
56      /* 
57       * Only return an environment if it's already bee open in this process.
58       */
59      public EnvironmentImplInfo getExistingEnvironment(File   envHome) 
60          throws DatabaseException {
61  
62          return getEnvironment(envHome, null, false);
63      }
64  
65      /**
66       * Find a single environment, used by Environment handles and by command
67       * line utilities.
68       */
69      private synchronized
70          EnvironmentImplInfo getEnvironment(File   envHome,
71                                             EnvironmentConfig config,
72                                             boolean openIfNeeded)
73          throws DatabaseException {
74  
75          boolean found;
76          boolean firstHandle = false;
77  
78          EnvironmentImpl environmentImpl = null;
79          String   environmentKey = getEnvironmentMapKey(envHome);
80  
81          if (envs.containsKey(environmentKey)) {
82              /* Environment is resident */
83              environmentImpl = (EnvironmentImpl) envs.get(environmentKey);
84              if (!environmentImpl.isOpen()) {
85                  if (openIfNeeded) {
86                      environmentImpl.open();
87                      found = true;
88                  } else {
89                      found = false;
90                  }
91              } else {
92                  found = true;
93              }
94          } else {
95              if (openIfNeeded) {
96  
97                  /* 
98                   * Environment must be instantiated. If it can be created,
99                   * the configuration must have allowCreate set.
100                  */
101                 environmentImpl = new EnvironmentImpl(envHome, config);
102                 envs.put(environmentKey, environmentImpl);
103                 firstHandle = true;
104                 found = true;
105             } else {
106                 found = false;
107             }
108         }
109 
110         if (found) {
111             return new EnvironmentImplInfo(environmentImpl, firstHandle);
112         } else {
113             return new EnvironmentImplInfo(null, false);
114         }
115     }
116 
117 
118     /**
119      * Remove a EnvironmentImpl from the pool because it's been closed.
120      */
121     void remove(File   envHome)
122         throws DatabaseException {
123         envs.remove(getEnvironmentMapKey(envHome));
124     }
125 
126     public void clear() {
127         envs.clear();
128     }
129 
130     /* 
131      * Struct for returning two values.
132      */
133     public static class EnvironmentImplInfo {
134         public EnvironmentImpl envImpl;
135         public boolean firstHandle = false;
136 
137         EnvironmentImplInfo(EnvironmentImpl envImpl, boolean firstHandle) {
138             this.envImpl = envImpl;
139             this.firstHandle = firstHandle;
140         }
141     }
142 
143     /* Use the canonical path name for a normalized environment key. */
144     private String   getEnvironmentMapKey(File   file)
145         throws DatabaseException {
146         try {
147             return file.getCanonicalPath(); 
148         } catch (IOException   e) {
149             throw new DatabaseException(e);
150         }
151     }
152 }
153
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