lmdbjava/src/main/java/org/lmdbjava/BufferProxy.java at gh-267 · lmdbjava/lmdbjava · GitHub

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* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

* http://www.apache.org/licenses/LICENSE-2.0

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

package org.lmdbjava;

import static java.lang.Long.BYTES;

import static org.lmdbjava.DbiFlags.MDB_INTEGERKEY;

import static org.lmdbjava.DbiFlags.MDB_UNSIGNEDKEY;

import static org.lmdbjava.MaskedFlag.isSet;

import static org.lmdbjava.MaskedFlag.mask;

import java.util.Comparator;

import jnr.ffi.Pointer;

/**

* The strategy for mapping memory address to a given buffer type.

* <p>The proxy is passed to the {@link Env#create(org.lmdbjava.BufferProxy)} method and is

* subsequently used by every {@link Txn}, {@link Dbi} and {@link Cursor} associated with the {@link

* Env}.

* @param <T> buffer type

public abstract class BufferProxy<T> {

/** Size of a <code>MDB_val</code> pointer in bytes. */

protected static final int MDB_VAL_STRUCT_SIZE = BYTES * 2;

/** Offset from a pointer of the <code>MDB_val.mv_data</code> field. */

protected static final int STRUCT_FIELD_OFFSET_DATA = BYTES;

/** Offset from a pointer of the <code>MDB_val.mv_size</code> field. */

protected static final int STRUCT_FIELD_OFFSET_SIZE = 0;

/** Explicitly-defined default constructor to avoid warnings. */

protected BufferProxy() {}

/**

* Allocate a new buffer suitable for passing to {@link #out(java.lang.Object, jnr.ffi.Pointer)}.

* @return a buffer for passing to the <code>out</code> method

protected abstract T allocate();

/**

* Deallocate a buffer that was previously provided by {@link #allocate()}.

* @param buff the buffer to deallocate (required)

protected abstract void deallocate(T buff);

/**

* Obtain a copy of the bytes contained within the passed buffer.

* @param buffer a non-null buffer created by this proxy instance

* @return a copy of the bytes this buffer is currently representing

protected abstract byte[] getBytes(T buffer);

/**

* Get a suitable default {@link Comparator} given the provided flags.

* <p>The provided comparator must strictly match the lexicographical order of keys in the native

* LMDB database.

* @param flags for the database

* @return a comparator that can be used (never null)

protected Comparator<T> getComparator(DbiFlags... flags) {

final int intFlag = mask(flags);

return isSet(intFlag, MDB_INTEGERKEY) || isSet(intFlag, MDB_UNSIGNEDKEY)

? getUnsignedComparator()

: getSignedComparator();

}

/**

* Get a suitable default {@link Comparator} to compare numeric key values as signed.

* @return a comparator that can be used (never null)

protected abstract Comparator<T> getSignedComparator();

/**

* Get a suitable default {@link Comparator} to compare numeric key values as unsigned.

* @return a comparator that can be used (never null)

protected abstract Comparator<T> getUnsignedComparator();

/**

* Called when the <code>MDB_val</code> should be set to reflect the passed buffer. This buffer

* will have been created by end users, not {@link #allocate()}.

* @param buffer the buffer to write to <code>MDB_val</code>

* @param ptr the pointer to the <code>MDB_val</code>

* @return a transient pointer that must be kept alive, or null if none

protected abstract Pointer in(T buffer, Pointer ptr);

/**

* Called when the <code>MDB_val</code> should be set to reflect the passed buffer.

* @param buffer the buffer to write to <code>MDB_val</code>

* @param size the buffer size to write to <code>MDB_val</code>

* @param ptr the pointer to the <code>MDB_val</code>

* @return a transient pointer that must be kept alive, or null if none

protected abstract Pointer in(T buffer, int size, Pointer ptr);

/**

* Called when the <code>MDB_val</code> may have changed and the passed buffer should be modified

* to reflect the new <code>MDB_val</code>.

* @param buffer the buffer to write to <code>MDB_val</code>

* @param ptr the pointer to the <code>MDB_val</code>

* @return the buffer for <code>MDB_val</code>

protected abstract T out(T buffer, Pointer ptr);

/**

* Create a new {@link KeyVal} to hold pointers for this buffer proxy.

* @return a non-null key value holder

final KeyVal<T> keyVal() {

return new KeyVal<>(this);

}

lmdbjava/src/main/java/org/lmdbjava/BufferProxy.java at gh-267 · lmdbjava/lmdbjava · GitHub

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