OpenJDK 27 · java.util.prefs.FileSystemPreferences · APIdia, the JavaDoc alternative

Modifier and Type	Class and Description
private abstract static class	FileSystemPreferences.Change Represents a change to a preference.
private static class	FileSystemPreferences.NodeCreate Represents the creation of this node.
private class	FileSystemPreferences.Put Represents a preference put.
private class	FileSystemPreferences.Remove Represents a preference remove.

Field Summary

Modifier and Type	Field and Description
pack-priv final List<FileSystemPreferences.Change>	changeLog A list of all uncommitted preference changes.
private final File	dir The directory representing this preference node.
private static final int	EACCES Unix error code for denied access.
private static final int	EAGAIN Unix error code for locked file.
private static final String[]	EMPTY_STRING_ARRAY Hides java.util.prefs.AbstractPreferences.EMPTY_STRING_ARRAY.
private static final int	ERROR_CODE
private static final int	INIT_SLEEP_TIME Initial time between lock attempts, in ms.
private static boolean	isSystemRootModified
private static boolean	isSystemRootWritable
private final boolean	isUserNode
private static boolean	isUserRootModified Flag, which indicated whether userRoot was modified by another VM
private static boolean	isUserRootWritable
private long	lastSyncTime The last modification time of the file backing this node at the time that prefCache was last synchronized (or initially read).
private static final int	LOCK_HANDLE
private static final int	MAX_ATTEMPTS Maximum number of lock attempts.
pack-priv FileSystemPreferences.NodeCreate	nodeCreate NodeCreate object for this node.
private Map<String, String>	prefsCache Locally cached preferences for this node (includes uncommitted changes).
private final File	prefsFile The file representing this preference node's preferences.
private static final int	SYNC_INTERVAL Sync interval in seconds.
private static final Timer	syncTimer
pack-priv static File	systemLockFile The lock file for the system tree.
private static volatile Preferences	systemRoot The system root.
private static File	systemRootDir Directory for system preferences.
private static int	systemRootLockHandle Unix lock handle for systemRoot.
private static File	systemRootModFile
private static long	systemRootModTime Keeps track of systemRoot modification time.
private final File	tmpFile A temporary file used for saving changes to preferences.
private static final int	USER_READ_WRITE Unix user write/read permission
private static final int	USER_RW_ALL_READ
private static final int	USER_RWX
private static final int	USER_RWX_ALL_RX
pack-priv static File	userLockFile The lock file for the user tree.
private static volatile Preferences	userRoot The user root.
private static File	userRootDir Directory for user preferences.
private static int	userRootLockHandle Unix lock handle for userRoot.
private static File	userRootModFile File, which keeps track of global modifications of userRoot.
private static long	userRootModTime Keeps track of userRoot modification time.

Inherited from java.util.prefs.AbstractPreferences:: CODE_POINT_U0000 lock newNode parent

Constructor Summary

Access	Constructor and Description
private	FileSystemPreferences(boolean user) Special constructor for roots (both user and system).
private	FileSystemPreferences(FileSystemPreferences parent, String name) Construct a new FileSystemPreferences instance with the specified parent node and name.

Method Summary

Modifier and Type	Method and Description
private static void	addShutdownHook()
private static byte[]	byteArray(String s) Translate a string into a byte array by translating each character into two bytes, high-byte first ("big-endian").
private void	checkLockFile0ErrorCode(int errorCode) Checks if unlockFile0() returned an error.
protected String[]	childrenNamesSpi() Implements abstract java.util.prefs.AbstractPreferences.childrenNamesSpi. Returns the names of the children of this preference node.
protected AbstractPreferences	childSpi(String name) Implements abstract java.util.prefs.AbstractPreferences.childSpi. Returns the named child of this preference node, creating it if it does not already exist.
private static native int	chmod(String fileName, int permission) Changes UNIX file permissions.
private static String	dirName(String nodeName) Returns the directory name corresponding to the specified node name.
public void	flush() Overrides java.util.prefs.AbstractPreferences.flush. Implements the `flush` method as per the specification in `Preferences#flush()`.
protected void	flushSpi() Implements abstract java.util.prefs.AbstractPreferences.flushSpi. This method is invoked with this node locked.
private static PlatformLogger	getLogger() Returns logger for error messages.
protected String	getSpi(String key) Implements abstract java.util.prefs.AbstractPreferences.getSpi. Return the value associated with the specified key at this preference node, or `null` if there is no association for this key, or the association cannot be determined at this time.
pack-priv static Preferences	getSystemRoot()
pack-priv static Preferences	getUserRoot()
private void	initCacheIfNecessary() Initialize prefsCache if it has yet to be initialized.
private static boolean	isDirChar(char ch) Returns true if the specified character is appropriate for use in Unix directory names.
public boolean	isUserNode() Overrides java.util.prefs.AbstractPreferences.isUserNode. Implements the `isUserNode` method as per the specification in `Preferences#isUserNode()`.
protected String[]	keysSpi() Implements abstract java.util.prefs.AbstractPreferences.keysSpi. Returns all of the keys that have an associated value in this preference node.
private void	loadCache() Attempt to load prefsCache from the backing store.
private static void	loadPrefsLib()
private boolean	lockFile(boolean shared) Try to acquire the appropriate file lock (user or system).
private static native int[]	Returns: Returns a lock handle, used to unlock the file. lockFile0(String Absolute file name of the lock file. fileName, int permission, boolean shared) Locks file using UNIX file locking.
private static String	nodeName(String dirName) Returns the node name corresponding to the specified directory name.
protected void	putSpi(String key, String value) Implements abstract java.util.prefs.AbstractPreferences.putSpi. Put the given key-value association into this preference node.
public void	removeNode() Overrides java.util.prefs.AbstractPreferences.removeNode. Implements the `removeNode()` method as per the specification in `Preferences#removeNode()`.
protected void	removeNodeSpi() Implements abstract java.util.prefs.AbstractPreferences.removeNodeSpi. Called with file lock held (in addition to node locks).
protected void	removeSpi(String key) Implements abstract java.util.prefs.AbstractPreferences.removeSpi. Remove the association (if any) for the specified key at this preference node.
private void	replayChanges() Replay changeLog against prefsCache.
private static void	setupSystemRoot()
private static void	setupUserRoot()
public synchronized void	sync() Overrides java.util.prefs.AbstractPreferences.sync. Implements the `sync` method as per the specification in `Preferences#sync()`.
protected void	syncSpi() Implements abstract java.util.prefs.AbstractPreferences.syncSpi. This method is invoked with this node locked.
private static void	syncWorld()
private void	unlockFile() Release the appropriate file lock (user or system).
private static native int	Returns: Returns zero if OK, UNIX error code if failure. unlockFile0(int Handle to the file lock. lockHandle) Unlocks file previously locked by lockFile0().
private void	writeBackCache() Attempt to write back prefsCache to the backing store.

Field Detail

changeLog	back to summary
pack-priv final List<FileSystemPreferences.Change> changeLog A list of all uncommitted preference changes. The elements in this list are of type PrefChange. If this node is concurrently modified on disk by another VM, the two sets of changes are merged when this node is sync'ed by overwriting our prefsCache with the preference map last written out to disk (by the other VM), and then replaying this change log against that map. The resulting map is then written back to the disk.

changeLog

back to summary

pack-priv final List<FileSystemPreferences.Change> changeLog

A list of all uncommitted preference changes. The elements in this list are of type PrefChange. If this node is concurrently modified on disk by another VM, the two sets of changes are merged when this node is sync'ed by overwriting our prefsCache with the preference map last written out to disk (by the other VM), and then replaying this change log against that map. The resulting map is then written back to the disk.

dir	back to summary
private final File dir The directory representing this preference node. There is no guarantee that this directory exits, as another VM can delete it at any time that it (the other VM) holds the file-lock. While the root node cannot be deleted, it may not yet have been created, or the underlying directory could have been deleted accidentally.

EACCES	back to summary
private static final int EACCES Unix error code for denied access.

EAGAIN	back to summary
private static final int EAGAIN Unix error code for locked file.

EMPTY_STRING_ARRAY	back to summary
private static final String[] EMPTY_STRING_ARRAY Hides java.util.prefs.AbstractPreferences.EMPTY_STRING_ARRAY.

ERROR_CODE	back to summary
private static final int ERROR_CODE

INIT_SLEEP_TIME	back to summary
private static final int INIT_SLEEP_TIME Initial time between lock attempts, in ms. The time is doubled after each failing attempt (except the first).

isSystemRootModified	back to summary
private static boolean isSystemRootModified

isSystemRootWritable	back to summary
private static boolean isSystemRootWritable

isUserNode	back to summary
private final boolean isUserNode

isUserRootModified	back to summary
private static boolean isUserRootModified Flag, which indicated whether userRoot was modified by another VM

isUserRootWritable	back to summary
private static boolean isUserRootWritable

lastSyncTime	back to summary
private long lastSyncTime The last modification time of the file backing this node at the time that prefCache was last synchronized (or initially read). This value is set before reading the file, so it's conservative; the actual timestamp could be (slightly) higher. A value of zero indicates that we were unable to initialize prefsCache from the disk, or have not yet attempted to do so. (If prefsCache is non-null, it indicates the former; if it's null, the latter.)

lastSyncTime

back to summary

private long lastSyncTime

The last modification time of the file backing this node at the time that prefCache was last synchronized (or initially read). This value is set *before* reading the file, so it's conservative; the actual timestamp could be (slightly) higher. A value of zero indicates that we were unable to initialize prefsCache from the disk, or have not yet attempted to do so. (If prefsCache is non-null, it indicates the former; if it's null, the latter.)

LOCK_HANDLE	back to summary
private static final int LOCK_HANDLE

MAX_ATTEMPTS	back to summary
private static final int MAX_ATTEMPTS Maximum number of lock attempts.

nodeCreate	back to summary
pack-priv FileSystemPreferences.NodeCreate nodeCreate NodeCreate object for this node.

prefsCache	back to summary
private Map<String, String> prefsCache Locally cached preferences for this node (includes uncommitted changes). This map is initialized with from disk when the first get or put operation occurs on this node. It is synchronized with the corresponding disk file (prefsFile) by the sync operation. The initial value is read without acquiring the file-lock.

prefsFile	back to summary
private final File prefsFile The file representing this preference node's preferences. The file format is undocumented, and subject to change from release to release, but I'm sure that you can figure it out if you try real hard.

SYNC_INTERVAL	back to summary
private static final int SYNC_INTERVAL Sync interval in seconds.

syncTimer	back to summary
private static final Timer syncTimer

systemLockFile	back to summary
pack-priv static File systemLockFile The lock file for the system tree.

systemRoot	back to summary
private static volatile Preferences systemRoot The system root.

systemRootDir	back to summary
private static File systemRootDir Directory for system preferences.

systemRootLockHandle	back to summary
private static int systemRootLockHandle Unix lock handle for systemRoot. Zero, if unlocked.

systemRootModFile	back to summary
private static File systemRootModFile

systemRootModTime	back to summary
private static long systemRootModTime Keeps track of systemRoot modification time. This time is reset to zero after system reboot, and is increased by 1 second each time systemRoot is modified.

tmpFile	back to summary
private final File tmpFile A temporary file used for saving changes to preferences. As part of the sync operation, changes are first saved into this file, and then atomically renamed to prefsFile. This results in an atomic state change from one valid set of preferences to another. The file-lock is held for the duration of this transformation.

USER_READ_WRITE	back to summary
private static final int USER_READ_WRITE Unix user write/read permission

USER_RW_ALL_READ	back to summary
private static final int USER_RW_ALL_READ

USER_RWX	back to summary
private static final int USER_RWX

USER_RWX_ALL_RX	back to summary
private static final int USER_RWX_ALL_RX

userLockFile	back to summary
pack-priv static File userLockFile The lock file for the user tree.

userRoot	back to summary
private static volatile Preferences userRoot The user root.

userRootDir	back to summary
private static File userRootDir Directory for user preferences.

userRootLockHandle	back to summary
private static int userRootLockHandle Unix lock handle for userRoot. Zero, if unlocked.

userRootModFile	back to summary
private static File userRootModFile File, which keeps track of global modifications of userRoot.

userRootModTime	back to summary
private static long userRootModTime Keeps track of userRoot modification time. This time is reset to zero after UNIX reboot, and is increased by 1 second each time userRoot is modified.

Constructor Detail

FileSystemPreferences	back to summary
private FileSystemPreferences(boolean user) Special constructor for roots (both user and system). This constructor will only be called twice, by the static initializer.

FileSystemPreferences	back to summary
private FileSystemPreferences(FileSystemPreferences parent, String name) Construct a new FileSystemPreferences instance with the specified parent node and name. This constructor, called from childSpi, is used to make every node except for the two //roots.

Method Detail

addShutdownHook	back to summary
private static void addShutdownHook()

byteArray	back to summary
private static byte[] byteArray(String s) Translate a string into a byte array by translating each character into two bytes, high-byte first ("big-endian").

checkLockFile0ErrorCode	back to summary
private void checkLockFile0ErrorCode(int errorCode) throws SecurityException Checks if unlockFile0() returned an error. Throws a SecurityException, if access denied. Logs a warning otherwise.

childrenNamesSpi back to summary

childrenNamesSpi	back to summary
protected String[] childrenNamesSpi() Implements abstract java.util.prefs.AbstractPreferences.childrenNamesSpi. Doc from java.util.prefs.AbstractPreferences.childrenNamesSpi. Returns the names of the children of this preference node. (The returned array will be of size zero if this node has no children.) This method need not return the names of any nodes already cached, but may do so without harm. This method is invoked with the lock on this node held. If this node throws a `BackingStoreException`, the exception will propagate out beyond the enclosing `childrenNames()` invocation.

protected String[] childrenNamesSpi()

Implements abstract java.util.prefs.AbstractPreferences.childrenNamesSpi.

Doc from java.util.prefs.AbstractPreferences.childrenNamesSpi.

Returns the names of the children of this preference node. (The returned array will be of size zero if this node has no children.) This method need not return the names of any nodes already cached, but may do so without harm.

This method is invoked with the lock on this node held.

If this node throws a BackingStoreException, the exception will propagate out beyond the enclosing childrenNames() invocation.

childSpi back to summary

childSpi	back to summary
protected AbstractPreferences childSpi(String name) Implements abstract java.util.prefs.AbstractPreferences.childSpi. Doc from java.util.prefs.AbstractPreferences.childSpi. Returns the named child of this preference node, creating it if it does not already exist. It is guaranteed that `name` is non-null, non-empty, does not contain the slash character ('/'), and is no longer than `MAX_NAME_LENGTH` characters. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for any of these things.) Finally, it is guaranteed that the named node has not been returned by a previous invocation of this method or `getChild(String)` after the last time that it was removed. In other words, a cached value will always be used in preference to invoking this method. Subclasses need not maintain their own cache of previously returned children. The implementer must ensure that the returned node has not been removed. If a like-named child of this node was previously removed, the implementer must return a newly constructed `AbstractPreferences` node; once removed, an `AbstractPreferences` node cannot be "resuscitated." If this method causes a node to be created, this node is not guaranteed to be persistent until the `flush` method is invoked on this node or one of its ancestors (or descendants). This method is invoked with the lock on this node held.

protected AbstractPreferences childSpi(String name)

Implements abstract java.util.prefs.AbstractPreferences.childSpi.

Doc from java.util.prefs.AbstractPreferences.childSpi.

Returns the named child of this preference node, creating it if it does not already exist. It is guaranteed that name is non-null, non-empty, does not contain the slash character ('/'), and is no longer than MAX_NAME_LENGTH characters. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for any of these things.)

Finally, it is guaranteed that the named node has not been returned by a previous invocation of this method or getChild(String) after the last time that it was removed. In other words, a cached value will always be used in preference to invoking this method. Subclasses need not maintain their own cache of previously returned children.

The implementer must ensure that the returned node has not been removed. If a like-named child of this node was previously removed, the implementer must return a newly constructed AbstractPreferences node; once removed, an AbstractPreferences node cannot be "resuscitated."

If this method causes a node to be created, this node is not guaranteed to be persistent until the flush method is invoked on this node or one of its ancestors (or descendants).

This method is invoked with the lock on this node held.

chmod	back to summary
private static native int chmod(String fileName, int permission) Changes UNIX file permissions.

dirName	back to summary
private static String dirName(String nodeName) Returns the directory name corresponding to the specified node name. Generally, this is just the node name. If the node name includes inappropriate characters (as per isDirChar) it is translated to Base64. with the underscore character ('_', 0x5f) prepended.

flush back to summary

public void flush() throws BackingStoreException

Overrides java.util.prefs.AbstractPreferences.flush.

Doc from java.util.prefs.AbstractPreferences.flush.

Implements the flush method as per the specification in Preferences#flush().

This implementation calls a recursive helper method that locks this node, invokes flushSpi() on it, unlocks this node, and recursively invokes this method on each "cached child." A cached child is a child of this node that has been created in this VM and not subsequently removed. In effect, this method does a depth first traversal of the "cached subtree" rooted at this node, calling flushSpi() on each node in the subTree while only that node is locked. Note that flushSpi() is invoked top-down.

If this method is invoked on a node that has been removed with the removeNode() method, flushSpi() is invoked on this node, but not on others.

Exceptions

BackingStoreException:: if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.

flushSpi back to summary

protected void flushSpi() throws BackingStoreException

Implements abstract java.util.prefs.AbstractPreferences.flushSpi.

Doc from java.util.prefs.AbstractPreferences.flushSpi.

This method is invoked with this node locked. The contract of this method is to force any cached changes in the contents of this preference node to the backing store, guaranteeing their persistence. (It is perfectly possible that this node does not exist on the backing store, either because it has been deleted by another VM, or because it has not yet been created.) Note that this method should not flush the preferences in any subnodes of this node. If the backing store naturally flushes an entire subtree at once, the implementer is encouraged to override flush(), rather than merely overriding this method.

If this node throws a BackingStoreException, the exception will propagate out beyond the enclosing flush() invocation.

Exceptions

BackingStoreException:: if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.

getLogger	back to summary
private static PlatformLogger getLogger() Returns logger for error messages. Backing store exceptions are logged at WARNING level.

getSpi back to summary

protected String getSpi(String key)

Implements abstract java.util.prefs.AbstractPreferences.getSpi.

Doc from java.util.prefs.AbstractPreferences.getSpi.

Return the value associated with the specified key at this preference node, or null if there is no association for this key, or the association cannot be determined at this time. It is guaranteed that key is non-null. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for either of these things.)

Generally speaking, this method should not throw an exception under any circumstances. If, however, if it does throw an exception, the exception will be intercepted and treated as a null return value.

This method is invoked with the lock on this node held.

getSystemRoot	back to summary
pack-priv static Preferences getSystemRoot()

getUserRoot	back to summary
pack-priv static Preferences getUserRoot()

initCacheIfNecessary

back to summary

private void initCacheIfNecessary()

Initialize prefsCache if it has yet to be initialized. When this method returns, prefsCache will be non-null. If the data was successfully read from the file, lastSyncTime will be updated. If prefsCache was null, but it was impossible to read the file (because it didn't exist or for any other reason) prefsCache will be initialized to an empty, modifiable Map, and lastSyncTime remain zero.

isDirChar	back to summary
private static boolean isDirChar(char ch) Returns true if the specified character is appropriate for use in Unix directory names. A character is appropriate if it's a printable ASCII character (> 0x1f && < 0x7f) and unequal to slash ('/', 0x2f), dot ('.', 0x2e), or underscore ('_', 0x5f).

isUserNode back to summary

public boolean isUserNode()

Overrides java.util.prefs.AbstractPreferences.isUserNode.

Doc from java.util.prefs.AbstractPreferences.isUserNode.

Implements the isUserNode method as per the specification in Preferences#isUserNode().

This implementation compares this node's root node (which is stored in a private field) with the value returned by Preferences#userRoot(). If the two object references are identical, this method returns true.

keysSpi back to summary

protected String[] keysSpi()

Implements abstract java.util.prefs.AbstractPreferences.keysSpi.

Doc from java.util.prefs.AbstractPreferences.keysSpi.

Returns all of the keys that have an associated value in this preference node. (The returned array will be of size zero if this node has no preferences.) It is guaranteed that this node has not been removed.

This method is invoked with the lock on this node held.

If this node throws a BackingStoreException, the exception will propagate out beyond the enclosing keys() invocation.

loadCache

back to summary

private void loadCache() throws BackingStoreException

Attempt to load prefsCache from the backing store. If the attempt succeeds, lastSyncTime will be updated (the new value will typically correspond to the data loaded into the map, but it may be less, if another VM is updating this node concurrently). If the attempt fails, a BackingStoreException is thrown and both prefsCache and lastSyncTime are unaffected by the call.

loadPrefsLib	back to summary
private static void loadPrefsLib() Annotations @SuppressWarnings:restricted

lockFile

back to summary

private boolean lockFile(boolean shared) throws SecurityException

Try to acquire the appropriate file lock (user or system). If the initial attempt fails, several more attempts are made using an exponential backoff strategy. If all attempts fail, this method returns false.

Exceptions

SecurityException:: if file access denied.

lockFile0

back to summary

private static native int[] lockFile0(String fileName, int permission, boolean shared)

Locks file using UNIX file locking.

Parameters

fileName:String: Absolute file name of the lock file.

Returns:int[]

Returns a lock handle, used to unlock the file.

nodeName	back to summary
private static String nodeName(String dirName) Returns the node name corresponding to the specified directory name. (Inverts the transformation of dirName(String).

putSpi back to summary

protected void putSpi(String key, String value)

Implements abstract java.util.prefs.AbstractPreferences.putSpi.

Doc from java.util.prefs.AbstractPreferences.putSpi.

Put the given key-value association into this preference node. It is guaranteed that key and value are non-null and of legal length. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for any of these things.)

This method is invoked with the lock on this node held.

removeNode back to summary

public void removeNode() throws BackingStoreException

Overrides java.util.prefs.AbstractPreferences.removeNode.

Doc from java.util.prefs.AbstractPreferences.removeNode.

Implements the removeNode() method as per the specification in Preferences#removeNode().

This implementation checks to see that this node is the root; if so, it throws an appropriate exception. Then, it locks this node's parent, and calls a recursive helper method that traverses the subtree rooted at this node. The recursive method locks the node on which it was called, checks that it has not already been removed, and then ensures that all of its children are cached: The childrenNamesSpi() method is invoked and each returned child name is checked for containment in the child-cache. If a child is not already cached, the childSpi(String) method is invoked to create a Preferences instance for it, and this instance is put into the child-cache. Then the helper method calls itself recursively on each node contained in its child-cache. Next, it invokes removeNodeSpi(), marks itself as removed, and removes itself from its parent's child-cache. Finally, if there are any node change listeners, it enqueues a notification event for processing by the event dispatch thread.

Note that the helper method is always invoked with all ancestors up to the "closest non-removed ancestor" locked.

Exceptions

BackingStoreException:: if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.

removeNodeSpi

back to summary

protected void removeNodeSpi() throws BackingStoreException

Implements abstract java.util.prefs.AbstractPreferences.removeNodeSpi.

Called with file lock held (in addition to node locks).

Exceptions

BackingStoreException:

Doc from java.util.prefs.AbstractPreferences.removeNodeSpi.

if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.

removeSpi back to summary

protected void removeSpi(String key)

Implements abstract java.util.prefs.AbstractPreferences.removeSpi.

Doc from java.util.prefs.AbstractPreferences.removeSpi.

Remove the association (if any) for the specified key at this preference node. It is guaranteed that key is non-null. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for either of these things.)

This method is invoked with the lock on this node held.

replayChanges	back to summary
private void replayChanges() Replay changeLog against prefsCache.

setupSystemRoot	back to summary
private static void setupSystemRoot()

setupUserRoot	back to summary
private static void setupUserRoot()

sync back to summary

public synchronized void sync() throws BackingStoreException

Overrides java.util.prefs.AbstractPreferences.sync.

Doc from java.util.prefs.AbstractPreferences.sync.

Implements the sync method as per the specification in Preferences#sync().

This implementation calls a recursive helper method that locks this node, invokes syncSpi() on it, unlocks this node, and recursively invokes this method on each "cached child." A cached child is a child of this node that has been created in this VM and not subsequently removed. In effect, this method does a depth first traversal of the "cached subtree" rooted at this node, calling syncSpi() on each node in the subTree while only that node is locked. Note that syncSpi() is invoked top-down.

Exceptions

BackingStoreException:: if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.

syncSpi back to summary

protected void syncSpi() throws BackingStoreException

Implements abstract java.util.prefs.AbstractPreferences.syncSpi.

Doc from java.util.prefs.AbstractPreferences.syncSpi.

This method is invoked with this node locked. The contract of this method is to synchronize any cached preferences stored at this node with any stored in the backing store. (It is perfectly possible that this node does not exist on the backing store, either because it has been deleted by another VM, or because it has not yet been created.) Note that this method should not synchronize the preferences in any subnodes of this node. If the backing store naturally syncs an entire subtree at once, the implementer is encouraged to override sync(), rather than merely overriding this method.

If this node throws a BackingStoreException, the exception will propagate out beyond the enclosing sync() invocation.

Exceptions

BackingStoreException:: if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.

syncWorld	back to summary
private static void syncWorld()

unlockFile

back to summary

private void unlockFile()

Release the appropriate file lock (user or system).

Exceptions

SecurityException:: if file access denied.

unlockFile0

back to summary

private static native int unlockFile0(int lockHandle)

Unlocks file previously locked by lockFile0().

Parameters

lockHandle:int: Handle to the file lock.

Returns:int

Returns zero if OK, UNIX error code if failure.

writeBackCache

back to summary

private void writeBackCache() throws BackingStoreException

Attempt to write back prefsCache to the backing store. If the attempt succeeds, lastSyncTime will be updated (the new value will correspond exactly to the data thust written back, as we hold the file lock, which prevents a concurrent write. If the attempt fails, a BackingStoreException is thrown and both the backing store (prefsFile) and lastSyncTime will be unaffected by this call. This call will NEVER leave prefsFile in a corrupt state.

pack-priv Class FileSystemPreferences

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private abstract Class FileSystemPreferences.Change

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private Class FileSystemPreferences.NodeCreate

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private Class FileSystemPreferences.Put

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private Class FileSystemPreferences.Remove

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