backing

backing

Persistent storage for typed arrays / buffers.

What?

Provides a virtual address space for large segments of memory via ArrayBuffers, and operations for alloc()ing and free()ing within the address space, optionally via a simple reference counting garbage collector. These large segments of data can optionally be automatically persisted to disk, (and shared with other processes!) via mmap.

For related work which builds on top of this see reign - a persistent, typed objects system.

Installation

Install via npm.

npm install backing

Usage

import Backing from "backing";

const store = new Backing({
  name: "demo",
  /**
   * The number of bytes which will be preallocated at a time.
   * Note that this imposes an upper bound on the largest possible
   * size of a block in the store.
   * On the server you should usually set this to the largest permissible value: 2Gb.
   */
  arenaSize: 16 * 1024 * 1024, // 16Mb
  arenaSource: {
    type: 'mmap', // Can also be 'array-buffer'
    /**
     * The full path to the directory containing the data files.
     */
    dirname: __dirname + '/data',
    /**
     * The number of garbage collection cycles a value should persist for until it is cleaned up.
     */
    lifetime: 2
  }
});

async function run () {
  await store.init();

  const address = store.alloc(64);

  store.setInt32(address, 123);

  console.log(store.getInt32(address)); // 123

  store.free(address); // 64

  // Garbage collector

  const address2 = store.gc.alloc(64);
  store.setFloat64(address2, 456.789);
  console.log(store.gc.sizeOf(address2));
  console.log(store.getFloat64(address2));

  store.gc.ref(address2); // Add a reference to our address

  store.gc.cycle(); // our value is preserved.

  store.gc.unref(address2); // Decrement the reference count, now 0.

  let freed = store.gc.cycle(); // our value is preserved but its cycle count is incremented.
  console.log(freed); // 0;

  freed = store.gc.cycle(); // our value is garbage collected because its cycle count reached 2.
  console.log(freed); // 64 + 16 = 80 bytes. The 16 bytes is the overhead of a garbage collectible block.
}

run();

License

Published by codemix under a permissive MIT License, see LICENSE.md.