Package org.h2.store

Class FileLock

java.lang.Object
org.h2.store.FileLock
All Implemented Interfaces:
Runnable
public class FileLock extends Object implements Runnable
The file lock is used to lock a database so that only one process can write to it. It uses a cooperative locking protocol. Usually a .lock.db file is used, but locking by creating a socket is supported as well.

  • Field Details

    • MAGIC

      private static final String MAGIC
      See Also:

    • FILE

      private static final String FILE
      See Also:

    • SOCKET

      private static final String SOCKET
      See Also:

    • RANDOM_BYTES

      private static final int RANDOM_BYTES
      See Also:

    • SLEEP_GAP

      private static final int SLEEP_GAP
      See Also:

    • TIME_GRANULARITY

      private static final int TIME_GRANULARITY
      See Also:

    • fileName

      private volatile String fileName
      The lock file name.

    • serverSocket

      private volatile ServerSocket serverSocket
      The server socket (only used when using the SOCKET mode).

    • locked

      private volatile boolean locked
      Whether the file is locked.

    • sleep

      private final int sleep
      The number of milliseconds to sleep after checking a file.

    • trace

      private final Trace trace
      The trace object.

    • lastWrite

      private long lastWrite
      The last time the lock file was written.

    • method

      private String method

    • properties

      private Properties properties

    • uniqueId

      private String uniqueId

    • watchdog

      private Thread watchdog

  • Constructor Details

    • FileLock

      public FileLock(TraceSystem traceSystem, String fileName, int sleep)
      Create a new file locking object.
      Parameters:
      traceSystem - the trace system to use
      fileName - the file name
      sleep - the number of milliseconds to sleep

  • Method Details

    • lock

      public void lock(FileLockMethod fileLockMethod)
      Lock the file if possible. A file may only be locked once.
      Parameters:
      fileLockMethod - the file locking method to use
      Throws:
      DbException - if locking was not successful

    • unlock

      public void unlock()
      Unlock the file. The watchdog thread is stopped. This method does nothing if the file is already unlocked.

    • setProperty

      public void setProperty(String key, String value)
      Add or change a setting to the properties. This call does not save the file.
      Parameters:
      key - the key
      value - the value

    • save

      public Properties save()
      Save the lock file.
      Returns:
      the saved properties

    • aggressiveLastModified

      private static long aggressiveLastModified(String fileName)
      Aggressively read last modified time, to work-around remote filesystems.
      Parameters:
      fileName - file name to check
      Returns:
      last modified date/time in milliseconds UTC

    • checkServer

      private void checkServer()

    • load

      public Properties load()
      Load the properties file.
      Returns:
      the properties

    • waitUntilOld

      private void waitUntilOld()

    • setUniqueId

      private void setUniqueId()

    • lockFile

      private void lockFile()

    • lockSocket

      private void lockSocket()

    • sleep

      private static void sleep(int time)

    • getExceptionFatal

      private static DbException getExceptionFatal(String reason, Throwable t)

    • getExceptionAlreadyInUse

      private DbException getExceptionAlreadyInUse(String reason)

    • getFileLockMethod

      public static FileLockMethod getFileLockMethod(String method)
      Get the file locking method type given a method name.
      Parameters:
      method - the method name
      Returns:
      the method type
      Throws:
      DbException - if the method name is unknown

    • getUniqueId

      public String getUniqueId()

    • run

      public void run()
      Specified by:
      run in interface Runnable