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net.captp.tables
Class CommTable

java.lang.Object
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 +--net.captp.tables.CommTable

Direct Known Subclasses:

AnswersTable, ExportsTable, ImportsTable, QuestionsTable

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public abstract class CommTable

extends Object

Untamed: Just some common mechanism made available to the CommTable implementations.

CommTables are defined in terms of indices (always positive), not position. At a higher level, positions use positive or negative to encode choice of table (questions vs imports, answers vs exports). This can be a bit confusing because CommTable internally uses negated indices for free list entries, and these two uses of negation are completely independent. The rest of CapTP depends on the tables, but for the sake of unit testing, each table stands alone to the greatest reasonable degree. Since AnswersTable adds almost nothing to CommTable, you can unit test CommTable by testing AnswersTable.

Author:

Mark Miller

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ThePumpkin

private static final Object ThePumpkin

Used to indicate the absence of any other object

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INIT_CAPACITY

private static final int INIT_CAPACITY

Default initial capacity

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GROWTH_FACTOR

private static final int GROWTH_FACTOR

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mySize

private int mySize

How many allocated entries do I have?

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myCapacity

int myCapacity

What is the size of my parallel arrays?

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myFreeList

private int[] myFreeList

Keeps track of the allocation of my indices.

myFreeList[0] is unused and always has the value 0. For all i>= 1, if myFreeList[i]>= 1, it's an allocation count. Otherwise, let next := -myFreeList[i]. If next>= 1, it's the index of the next free entry in myFreeList. If next == 0, we're at the end of the list.

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myFreeHead

private int myFreeHead

Let first = -myFreeHead; If first>= 1, it's the index of the first free entry in myFreeList. If first == 0, the list is empty.

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myStuff

Object[] myStuff

The actual contents of the table.

CommTable

public CommTable()

Enabled: Starts will all inidices free.

smash

public void smash(Throwable problem)

Enabled: Drop all state and make sure nothing ever works again.

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size

public int size()

Enabled: How many allocated entries?

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isFree

boolean isFree(int index)

Is this index free? If it's past the end, yes. If it's before the beginning, it's not valid, so no.

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mustBeFree

public void mustBeFree(int index)

Enabled: Complain if not free

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mustBeAlloced

public void mustBeAlloced(int index)

Enabled: Complain if not allocated

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bigEnough

private int bigEnough(int index)

What the next capacity big enough to represent index?

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grow

private static Object grow(Object array,
 int capacity)

Returns array or a copy of array sized to capacity.

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growToHold

private void growToHold(int index)

Become big enough to hold index.

Newly added elements are on the (newly grown) free list.

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free

public void free(int index)

Enabled: Deallocates an allocated index.

Subclasses may override and send-super in order to clear their parallel arrays.

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incr

public void incr(int index)

Enabled: Increment index's allocation count.

index must already be allocated

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decr

public boolean decr(int index,
 int delta)

Enabled: Decrement index's allocation count delta, and free it if it reaches zero.

On entry, index must be allocated.

Returns:

whether the entry got freed

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alloc

private void alloc(int index)

Allocate a particular index.

On entry, index must be free.

Since the free list is singly linked, we can't generally do this in constant time. However, by far the typical case is for the requested index to be the same as the one that zero-argument alloc would have allocated, so we need merely assure that this case is constant time.

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get

public Object get(int index)

Enabled: Gets the object at the allocated index.

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put

public void put(int index,
 Object value)

Enabled:

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put

public void put(int index,
 Object value,
 boolean strict)

Enabled:

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bind

public int bind(Object value)

Enabled: Allocates a free index, put value there, and returns that index.

Subclasses may override and send-super to initialize their parallel arrays.

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__printOn

public void __printOn(TextWriter out)
 throws IOException

Enabled:

IOException

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