Databases
StackOverflow2013
Postsdbo
POThread Safe singleton class
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POThread Safe singleton class
    primarykey
    data
    text
    <p>I wrote a below Singleton class. I am not sure whether this is thread safe singleton class or not?</p> <pre><code>public class CassandraAstyanaxConnection { private static CassandraAstyanaxConnection _instance; private AstyanaxContext&lt;Keyspace&gt; context; private Keyspace keyspace; private ColumnFamily&lt;String, String&gt; emp_cf; public static synchronized CassandraAstyanaxConnection getInstance() { if (_instance == null) { _instance = new CassandraAstyanaxConnection(); } return _instance; } /** * Creating Cassandra connection using Astyanax client * */ private CassandraAstyanaxConnection() { context = new AstyanaxContext.Builder() .forCluster(ModelConstants.CLUSTER) .forKeyspace(ModelConstants.KEYSPACE) .withAstyanaxConfiguration(new AstyanaxConfigurationImpl() .setDiscoveryType(NodeDiscoveryType.RING_DESCRIBE) ) .withConnectionPoolConfiguration(new ConnectionPoolConfigurationImpl("MyConnectionPool") .setPort(9160) .setMaxConnsPerHost(1) .setSeeds("127.0.0.1:9160") ) .withAstyanaxConfiguration(new AstyanaxConfigurationImpl() .setCqlVersion("3.0.0") .setTargetCassandraVersion("1.2")) .withConnectionPoolMonitor(new CountingConnectionPoolMonitor()) .buildKeyspace(ThriftFamilyFactory.getInstance()); context.start(); keyspace = context.getEntity(); emp_cf = ColumnFamily.newColumnFamily( ModelConstants.COLUMN_FAMILY, StringSerializer.get(), StringSerializer.get()); } /** * returns the keyspace * * @return */ public Keyspace getKeyspace() { return keyspace; } public ColumnFamily&lt;String, String&gt; getEmp_cf() { return emp_cf; } } </code></pre> <p>Can anyone help me with this? Any thoughts on my above Singleton class will be of great help.</p> <p><strong>Updated Code:-</strong></p> <p>I am trying to incorporate Bohemian suggestion in my code. Here is the updated code, I got-</p> <pre><code>public class CassandraAstyanaxConnection { private static class ConnectionHolder { static final CassandraAstyanaxConnection connection = new CassandraAstyanaxConnection(); } public static CassandraAstyanaxConnection getInstance() { return ConnectionHolder.connection; } /** * Creating Cassandra connection using Astyanax client * */ private CassandraAstyanaxConnection() { context = new AstyanaxContext.Builder() .forCluster(ModelConstants.CLUSTER) .forKeyspace(ModelConstants.KEYSPACE) .withAstyanaxConfiguration(new AstyanaxConfigurationImpl() .setDiscoveryType(NodeDiscoveryType.RING_DESCRIBE) ) .withConnectionPoolConfiguration(new ConnectionPoolConfigurationImpl("MyConnectionPool") .setPort(9160) .setMaxConnsPerHost(1) .setSeeds("127.0.0.1:9160") ) .withAstyanaxConfiguration(new AstyanaxConfigurationImpl() .setCqlVersion("3.0.0") .setTargetCassandraVersion("1.2")) .withConnectionPoolMonitor(new CountingConnectionPoolMonitor()) .buildKeyspace(ThriftFamilyFactory.getInstance()); context.start(); keyspace = context.getEntity(); emp_cf = ColumnFamily.newColumnFamily( ModelConstants.COLUMN_FAMILY, StringSerializer.get(), StringSerializer.get()); } /** * returns the keyspace * * @return */ public Keyspace getKeyspace() { return keyspace; } public ColumnFamily&lt;String, String&gt; getEmp_cf() { return emp_cf; } } </code></pre> <p>Can anyone take a look and let me know if this time I got it right or not?</p> <p>Thanks for the help.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USarsenal
    1. USarsenal
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POThread Safe singleton class
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POThread Safe singleton class
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POThread Safe singleton class
      1. UStgkprog
      1. VTFavorite
    1. COYes it it thread-safe, as long as the `Keyspace` and `ColumnFamily` class are too. It's not optimal however, you're going to get a lot of contention on the class synchronization in getInstance(). You should look up the "enum singleton pattern".
      singulars
      1. POThread Safe singleton class
      1. USɲeuroburɳ
    2. COsee http://javarevisited.blogspot.in/2012/07/why-enum-singleton-are-better-in-java.html and http://stackoverflow.com/questions/427902/what-is-the-best-approach-for-using-an-enum-as-a-singleton-in-java and maybe answer your own question with new enum version of your class ty @eurobur for pointing this out
      singulars
      1. POThread Safe singleton class
      1. UStgkprog
    3. COjust use an enum
      singulars
      1. POThread Safe singleton class
      1. USNimChimpsky
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload