Package com.mckoi.store
Class AbstractStore
java.lang.Object
com.mckoi.store.AbstractStore
- All Implemented Interfaces:
Store
- Direct Known Subclasses:
JournalledFileStore
Provides an abstract implementation of Store. This implements a bin based
best-fit recycling algorithm. The store manages a structure that points to
bins of freed space of specific sizes. When an allocation is requested the
structure is searched for the first bin that contains an area that best fits
the size requested.
Provided the derived class supports safe atomic IO operations, this store is designed for robustness to the level that at no point is the store left in a unworkable (corrupt) state.
- Author:
- Tobias Downer
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected static final long
The offset into the file that the bin area starts.protected static final int
protected static final long
The offset into the file that the data areas start.protected static final long
The offset into the file of the 64 byte fixed area.protected long[]
The free bin list contains 128 entries pointing to the first available block in the bin.protected final byte[]
protected static final int
The magic value.protected boolean
True if this is read-only.protected long
The total amount of allocated space within this store since the store was openned.protected long
A pointer to the wilderness area (the last deleted area in the store), or -1 if there is no wilderness area. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprotected void
checkPointer
(long pointer) Checks the pointer is valid.void
close()
Closes the store.protected void
coalescArea
(long pointer, long size) Coalesc one or more areas into a larger area.createArea
(long size) Allocates a block of memory in the store of the specified size and returns an AreaWriter object that can be used to initialize the contents of the area.void
deleteArea
(long id) Deletes an area that was previously allocated by the 'createArea' method by the area id.protected abstract long
Returns a pointer to the end of the current data area.protected long
expandDataArea
(long minimum_size) Expands the data area by at least the minimum size given.Scans the area list, and any areas that aren't deleted and aren't found in the given ArrayList are returned as leaked areas.Returns a List of Long objects that contain a complete list of all areas in the store.getArea
(long id) Returns an object that allows for the contents of an area (represented by the 'id' parameter) to be read.protected void
getAreaHeader
(long pointer, long[] header) Sets the 'header' array with information from the header of the given pointer.getAreaInputStream
(long id) Returns an InputStream implementation that allows for the area with the given identifier to be read sequentially.getMutableArea
(long id) Returns an object that allows for the contents of an area (represented by the 'id' parameter) to be read and written.protected long
getNextAreaHeader
(long pointer, long[] header) Sets the 'header' array with information from the next header to the given pointer, and returns a pointer to the next area.protected long
getPreviousAreaHeader
(long pointer, long[] header) Sets the 'header' array with information from the previous header to the given pointer, and returns a pointer to the previous area.protected abstract void
Internally closes the backing area.protected abstract void
internalOpen
(boolean read_only) Internally opens the backing area.protected static boolean
isValidBoundarySize
(long size) Returns true if the given area size is valid.boolean
Returns true if the store was closed cleanly.boolean
open()
Opens the data store.void
openScanAndFix
(UserTerminal terminal) Opens/scans the store looking for any errors with the layout.protected void
readBins()
Reads the bins from the header information in the file.protected abstract int
readByteArrayFrom
(long position, byte[] buf, int off, int len) Reads a byte array from the given position in the file.protected abstract int
readByteFrom
(long position) Reads a byte from the given position in the file.protected void
reboundArea
(long pointer, long[] header, boolean write_headers) Rebounds the given area with the given header information.protected abstract void
setDataAreaSize
(long length) Sets the size of the data area.protected void
splitArea
(long pointer, long new_boundary) Splits an area pointed to by 'pointer' at a new boundary point.void
Performs an extensive lookup on all the tables in this store and sets a number of properties in the given HashMap (property name(String) -> property description(Object)).long
Returns the total allocated space since the file was openned.protected void
Updates all bins to the data area header area.protected void
writeBinIndex
(int index) Updates the given bin index to the data area header area.protected abstract void
writeByteArrayTo
(long position, byte[] buf, int off, int len) Writes a byte array to the given position in the file.protected abstract void
writeByteTo
(long position, int b) Writes a byte to the given position in the file.Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface com.mckoi.store.Store
lockForWrite, unlockForWrite
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Field Details
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free_bin_list
protected long[] free_bin_listThe free bin list contains 128 entries pointing to the first available block in the bin. If the list item contains -1 then there are no free blocks in the bin. -
wilderness_pointer
protected long wilderness_pointerA pointer to the wilderness area (the last deleted area in the store), or -1 if there is no wilderness area. -
read_only
protected boolean read_onlyTrue if this is read-only. -
total_allocated_space
protected long total_allocated_spaceThe total amount of allocated space within this store since the store was openned. Note that this could be a negative amount if more space was freed than allocated. -
DATA_AREA_OFFSET
protected static final long DATA_AREA_OFFSETThe offset into the file that the data areas start.- See Also:
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FIXED_AREA_OFFSET
protected static final long FIXED_AREA_OFFSETThe offset into the file of the 64 byte fixed area.- See Also:
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BIN_AREA_OFFSET
protected static final long BIN_AREA_OFFSETThe offset into the file that the bin area starts.- See Also:
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MAGIC
protected static final int MAGICThe magic value.- See Also:
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header_buf
protected final byte[] header_buf -
BIN_ENTRIES
protected static final int BIN_ENTRIES
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Constructor Details
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AbstractStore
protected AbstractStore(boolean read_only) Constructs the store.
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Method Details
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open
Opens the data store. Returns true if the store did not close cleanly.- Throws:
IOException
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close
Closes the store.- Throws:
IOException
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isValidBoundarySize
protected static boolean isValidBoundarySize(long size) Returns true if the given area size is valid. Currently the criteria for a valid boundary size is (size >= 24) and (size % 8 == 0) and (size invalid input: '<' 200 gigabytes) -
openScanAndFix
Opens/scans the store looking for any errors with the layout. If a problem with the store is detected, it attempts to fix it.- Throws:
IOException
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statsScan
Performs an extensive lookup on all the tables in this store and sets a number of properties in the given HashMap (property name(String) -> property description(Object)). This should be used for store diagnostics.Assume the store is open.
- Throws:
IOException
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getAllAreas
Returns a List of Long objects that contain a complete list of all areas in the store. This is useful for checking if a given pointer is valid or not. The returned list is sorted from start area to end area.- Specified by:
getAllAreas
in interfaceStore
- Throws:
IOException
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findAllocatedAreasNotIn
Scans the area list, and any areas that aren't deleted and aren't found in the given ArrayList are returned as leaked areas. This is a useful method for finding any leaks in the store.- Throws:
IOException
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totalAllocatedSinceStart
public long totalAllocatedSinceStart()Returns the total allocated space since the file was openned. -
internalOpen
Internally opens the backing area. If 'read_only' is true then the store is openned in read only mode.- Throws:
IOException
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internalClose
Internally closes the backing area.- Throws:
IOException
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readByteFrom
Reads a byte from the given position in the file.- Throws:
IOException
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readByteArrayFrom
protected abstract int readByteArrayFrom(long position, byte[] buf, int off, int len) throws IOException Reads a byte array from the given position in the file. Returns the number of bytes read.- Throws:
IOException
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writeByteTo
Writes a byte to the given position in the file.- Throws:
IOException
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writeByteArrayTo
protected abstract void writeByteArrayTo(long position, byte[] buf, int off, int len) throws IOException Writes a byte array to the given position in the file.- Throws:
IOException
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endOfDataAreaPointer
Returns a pointer to the end of the current data area.- Throws:
IOException
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setDataAreaSize
Sets the size of the data area.- Throws:
IOException
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checkPointer
Checks the pointer is valid.- Throws:
IOException
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readBins
Reads the bins from the header information in the file.- Throws:
IOException
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writeAllBins
Updates all bins to the data area header area.- Throws:
IOException
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writeBinIndex
Updates the given bin index to the data area header area.- Throws:
IOException
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getAreaHeader
Sets the 'header' array with information from the header of the given pointer.- Throws:
IOException
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getPreviousAreaHeader
Sets the 'header' array with information from the previous header to the given pointer, and returns a pointer to the previous area.- Throws:
IOException
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getNextAreaHeader
Sets the 'header' array with information from the next header to the given pointer, and returns a pointer to the next area.- Throws:
IOException
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reboundArea
Rebounds the given area with the given header information. If 'write_headers' is true, the header (header[0]) is changed. Note that this shouldn't be used to change the size of a chunk.- Throws:
IOException
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coalescArea
Coalesc one or more areas into a larger area. This alters the boundary of the area to encompass the given size.- Throws:
IOException
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expandDataArea
Expands the data area by at least the minimum size given. Returns the actual size the data area was expanded by.- Throws:
IOException
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splitArea
Splits an area pointed to by 'pointer' at a new boundary point.- Throws:
IOException
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createArea
Description copied from interface:Store
Allocates a block of memory in the store of the specified size and returns an AreaWriter object that can be used to initialize the contents of the area. Note that an area in the store is undefined until the 'finish' method is called in AreaWriter.- Specified by:
createArea
in interfaceStore
- Parameters:
size
- the amount of memory to allocate.- Returns:
- an AreaWriter object that allows the area to be setup.
- Throws:
IOException
- if not enough space available to create the area or the store is read-only.
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deleteArea
Description copied from interface:Store
Deletes an area that was previously allocated by the 'createArea' method by the area id. Once an area is deleted the resources may be reclaimed. The behaviour of this method is undefined if the id doesn't represent a valid area.- Specified by:
deleteArea
in interfaceStore
- Parameters:
id
- the identifier of the area to delete.- Throws:
IOException
- (optional) if the id is invalid or the area can not otherwise by deleted.
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getAreaInputStream
Description copied from interface:Store
Returns an InputStream implementation that allows for the area with the given identifier to be read sequentially. The behaviour of this method, and InputStream object, is undefined if the id doesn't represent a valid area.When 'id' is -1 then a fixed area (64 bytes in size) in the store is returned. The fixed area can be used to store important static static information.
- Specified by:
getAreaInputStream
in interfaceStore
- Parameters:
id
- the identifier of the area to read, or id = -1 is a 64 byte fixed area in the store.- Returns:
- an InputStream that allows the area to be read from the start.
- Throws:
IOException
- (optional) if the id is invalid or the area can not otherwise be accessed.
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getArea
Description copied from interface:Store
Returns an object that allows for the contents of an area (represented by the 'id' parameter) to be read. The behaviour of this method, and Area object, is undefined if the id doesn't represent a valid area.When 'id' is -1 then a fixed area (64 bytes in size) in the store is returned. The fixed area can be used to store important static static information.
- Specified by:
getArea
in interfaceStore
- Parameters:
id
- the identifier of the area to read, or id = -1 is a 64 byte fixed area in the store.- Returns:
- an Area object that allows access to the part of the store.
- Throws:
IOException
- (optional) if the id is invalid or the area can not otherwise be accessed.
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getMutableArea
Description copied from interface:Store
Returns an object that allows for the contents of an area (represented by the 'id' parameter) to be read and written. The behaviour of this method, and MutableArea object, is undefined if the id doesn't represent a valid area.When 'id' is -1 then a fixed area (64 bytes in size) in the store is returned. The fixed area can be used to store important static static information.
- Specified by:
getMutableArea
in interfaceStore
- Parameters:
id
- the identifier of the area to access, or id = -1 is a 64 byte fixed area in the store.- Returns:
- a MutableArea object that allows access to the part of the store.
- Throws:
IOException
- (optional) if the id is invalid or the area can not otherwise be accessed.
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lastCloseClean
public boolean lastCloseClean()Description copied from interface:Store
Returns true if the store was closed cleanly. This is important information that may need to be considered when reading information from the store. This is typically used to issue a scan on the data in the store when it is not closed cleanly.- Specified by:
lastCloseClean
in interfaceStore
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