FileBasedTimestampSynchronizer (JUG)

java.lang.Object
- org.safehaus.uuid.TimestampSynchronizer
- - org.safehaus.uuid.ext.FileBasedTimestampSynchronizer

```
public final class FileBasedTimestampSynchronizer
extends TimestampSynchronizer
```
Implementation of TimestampSynchronizer, which uses file system as the storage and locking mechanism.
Synchronization is achieved by obtaining an exclusive file locks on two specified lock files, and by using the files to store first "safe" timestamp value that the generator can use; alternating between one to use to ensure one of them always contains a valid timestamp. Latter is needed to guard against system clock moving backwards after UUID generator restart.
Note: this class will only work on JDK 1.4 and above, since it requires NIO package to do proper file locking (as well as new opening mode for RandomAccessFile).
Also note that it is assumed that the caller has taken care to synchronize access to method to be single-threaded. As such, none of the methods is explicitly synchronized here.

Constructor Summary

Constructors
Constructor and Description
`FileBasedTimestampSynchronizer()` Constructor that uses default values for names of files to use (files will get created in the current working directory), as well as for the update frequency value (10 seconds).
`FileBasedTimestampSynchronizer(File f1, File f2)`
`FileBasedTimestampSynchronizer(File f1, File f2, long interval)`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`deactivate()` Method `UUIDTimer` will call if this synchronizer object is being replaced by another synchronizer (or removed, that is, no more synchronization is to be done).
`protected static void`	`doDeactivate(org.safehaus.uuid.ext.LockedFile lf1, org.safehaus.uuid.ext.LockedFile lf2)`
`protected long`	`initialize()` This method is to be called only once by `UUIDTimer`.
`void`	`setUpdateInterval(long interval)`
`long`	`update(long now)` Method called by `UUIDTimer` to indicate that it has generated a timestamp value that is beyond last legal timestamp value.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - FileBasedTimestampSynchronizer
```
public FileBasedTimestampSynchronizer()
                               throws IOException
```
    Constructor that uses default values for names of files to use (files will get created in the current working directory), as well as for the update frequency value (10 seconds).
    
    Throws:
    
    IOException
  - FileBasedTimestampSynchronizer
```
public FileBasedTimestampSynchronizer(File f1,
                                      File f2)
                               throws IOException
```
    Throws:
    
    IOException
  - FileBasedTimestampSynchronizer
```
public FileBasedTimestampSynchronizer(File f1,
                                      File f2,
                                      long interval)
                               throws IOException
```
    Throws:
    
    IOException
- Method Detail
  - setUpdateInterval
```
public void setUpdateInterval(long interval)
```
  - initialize
```
protected long initialize()
                   throws IOException
```
    This method is to be called only once by UUIDTimer. It should fetch the persisted timestamp value, which indicates first timestamp value that is guaranteed NOT to have used by a previous incarnation. If it can not determine such value, it is to return 0L as a marker.
    
    Specified by:
    
    initialize in class TimestampSynchronizer
    
    Returns:
    
    First timestamp value that was NOT locked by lock files; 0L to indicate that no information was read.
    
    Throws:
    
    IOException
  - deactivate
```
public void deactivate()
                throws IOException
```
    Description copied from class: TimestampSynchronizer
    
    Method UUIDTimer will call if this synchronizer object is being replaced by another synchronizer (or removed, that is, no more synchronization is to be done). It will not be called if JVM terminates.
    
    Specified by:
    
    deactivate in class TimestampSynchronizer
    
    Throws:
    
    IOException
  - update
```
public long update(long now)
            throws IOException
```
    Description copied from class: TimestampSynchronizer
    
    Method called by UUIDTimer to indicate that it has generated a timestamp value that is beyond last legal timestamp value. The method should only return once it has "locked" specified timestamp value (and possible additional ones).
    
    Specified by:
    
    update in class TimestampSynchronizer
    
    Parameters:
    
    now - Timestamp value caller wants to use, and that the synchronizer is asked to protect.
    
    Returns:
    
    Timestamp value that the caller can NOT use. That is, all timestamp values prior to (less than) this value can be used ok, but this value and ones after can only be used by first calling update.
    
    Throws:
    
    IOException
  - doDeactivate
```
protected static void doDeactivate(org.safehaus.uuid.ext.LockedFile lf1,
                                   org.safehaus.uuid.ext.LockedFile lf2)
```

Class FileBasedTimestampSynchronizer

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

FileBasedTimestampSynchronizer

FileBasedTimestampSynchronizer

FileBasedTimestampSynchronizer

Method Detail

setUpdateInterval

initialize

deactivate

update

doDeactivate