com.qcloud.cos.internal

Enum FileLocks

java.lang.Object

java.lang.Enum<FileLocks>

com.qcloud.cos.internal.FileLocks

All Implemented Interfaces:

Serializable, Comparable<FileLocks>

public enum FileLocks
extends Enum<FileLocks>

An internal utility used to provide both inter and intra JVM file locking. This works well as long as this class is loaded with the same class loader in a JVM. Otherwise, intra-JVM file locking is not guaranteed.

Per javadoc of FileLock, "File locks are held on behalf of the entire Java virtual machine. They are not suitable for controlling access to a file by multiple threads within the same virtual machine."

Hence the need for this utility class.

Method Summary

Modifier and Type	Method and Description
static boolean	isFileLocked(File file) Returns true if the specified file is currently locked; false otherwise.
static boolean	lock(File file) Acquires an exclusive lock on the specified file, creating the file as necessary.
static boolean	unlock(File file) Unlocks a file previously locked via lock(File).
static FileLocks	valueOf(String name) Returns the enum constant of this type with the specified name.
static FileLocks[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Method Detail

values

public static FileLocks[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (FileLocks c : FileLocks.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static FileLocks valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null

lock

public static boolean lock(File file)

Acquires an exclusive lock on the specified file, creating the file as necessary. Caller of this method is responsible to call the unlock(File) method to prevent release leakage.

Returns:

true if the locking is successful; false otherwise.

Throws:

FileLockException - if we failed to lock the file

isFileLocked

public static boolean isFileLocked(File file)

Returns true if the specified file is currently locked; false otherwise.

unlock

public static boolean unlock(File file)

Unlocks a file previously locked via lock(File).

Returns:

true if the unlock is successful; false otherwise. Successful unlock means we have found and attempted to close the locking file channel, but ignoring the fact that the close operation may have actually failed.