net.java.truevfs.access

Enum ExpertFeature.Reason

java.lang.Object

java.lang.Enum<ExpertFeature.Reason>

net.java.truevfs.access.ExpertFeature.Reason

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable<ExpertFeature.Reason>

Enclosing class:

ExpertFeature

public static enum ExpertFeature.Reason
extends java.lang.Enum<ExpertFeature.Reason>

The reason why a feature should only be used by an expert.

Enum Constant Summary

Enum Constants

Enum Constant and Description
INJECTING_A_DIFFERENT_DETECTOR_FOR_THE_SAME_PATH_MAY_CORRUPT_DATA Injecting a different archive detector for the same virtual file system path may cause data corruption.
THE_PRESENCE_OR_ABSENCE_OF_SOME_OPTIONS_MAY_YIELD_UNWANTED_SIDE_EFFECTS The presence or absence of some synchronization options may yield unwanted side effects.

Method Summary

Modifier and Type	Method and Description
java.lang.String	toString()
static ExpertFeature.Reason	valueOf(java.lang.String name) Returns the enum constant of this type with the specified name.
static ExpertFeature.Reason[]	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, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

INJECTING_A_DIFFERENT_DETECTOR_FOR_THE_SAME_PATH_MAY_CORRUPT_DATA

public static final ExpertFeature.Reason INJECTING_A_DIFFERENT_DETECTOR_FOR_THE_SAME_PATH_MAY_CORRUPT_DATA

Injecting a different archive detector for the same virtual file system path may cause data corruption. This is because the behavior of the virtual file system is not only a pure function of the operation parameters, but also depends on the current configuration, the state of the virtual file system and ultimately the state of the underlying host or network file system.

The state of the virtual file system very much depends on the archive detector which has been previously used to access the same virtual file system path. If there is a mismatch between the injected archive detector and the previously used archive detector, then the result of an operation is hard to predict but you can expect to see spurious false positive or false negative archive file detection or even data corruption up to the point of total data loss!

This is particularly true for multithreaded applications: If a thread changes the archive detector which is associated with a given virtual file system path, then another thread may get an unexpected result when accessing the same virtual file system path, with all the after effects described above.

Now that you have been warned, here is a high-level strategy for effectively associating a different archive detector to a given virtual file system path:

1. Lock out any other thread from concurrently accessing the virtual file system path.
2. Totally clear the state associated with the virtual file system path in the Kernel by calling the method TVFS.umount(). Your best choice is the umount method with no parameters. However, if you have to do this selectively, make sure the filter parameter really covers the virtual file system path you want to access and the effective options are FsSyncOptions.UMOUNT.
3. Now access the virtual file system path with the new archive detector. Depending on the particular archive detector, this will trigger mounting the archive file system by the Kernel. The new archive detector is then associated with the given file system path.
4. Depending on which operation you have performed and whether the change of the archive detector shall be persistent or not, you may need to repeat the second step.
5. Unlock access to the virtual file system path for other threads to see the result. Mind you that these threads may still be using the old archive detector.

I leave it up to you to figure the details - again, this is an expert feature!

See Also:

Third Party Access

THE_PRESENCE_OR_ABSENCE_OF_SOME_OPTIONS_MAY_YIELD_UNWANTED_SIDE_EFFECTS

public static final ExpertFeature.Reason THE_PRESENCE_OR_ABSENCE_OF_SOME_OPTIONS_MAY_YIELD_UNWANTED_SIDE_EFFECTS

The presence or absence of some synchronization options may yield unwanted side effects. For example, if the FsSyncOption.CLEAR_CACHE is absent, then the selective entry cache doesn' get cleared and hence the state associated with a particular file system path may not get totally cleared. On the other hand, the presence of the FsSyncOption.FORCE_CLOSE_IO will forcibly close any open streams and channels (after some timeout), regardless if they are currently used by other threads or not.

Method Detail

values

public static ExpertFeature.Reason[] 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 (ExpertFeature.Reason c : ExpertFeature.Reason.values())
    System.out.println(c);

Returns:

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

valueOf

public static ExpertFeature.Reason valueOf(java.lang.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:

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

java.lang.NullPointerException - if the argument is null

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Enum<ExpertFeature.Reason>