nodejs/doc/api/smalloc.markdown

Smalloc

Stability: 1 - Experimental

Class: smalloc

Buffers are backed by a simple allocator that only handles the assignation of external raw memory. Smalloc exposes that functionality.

smalloc.alloc(length[, receiver][, type])

• length {Number} <= smalloc.kMaxLength
• receiver {Object} Default: new Object
• type {Enum} Default: Uint8

Returns receiver with allocated external array data. If no receiver is passed then a new Object will be created and returned.

This can be used to create your own Buffer-like classes. No other properties are set, so the user will need to keep track of other necessary information (e.g. length of the allocation).

function SimpleData(n) {
  this.length = n;
  smalloc.alloc(this.length, this);
}

SimpleData.prototype = { /* ... */ };

It only checks if the receiver is an Object, and also not an Array. Because of this it is possible to allocate external array data to more than a plain Object.

function allocMe() { }
smalloc.alloc(3, allocMe);

// { [Function allocMe] '0': 0, '1': 0, '2': 0 }

v8 does not support allocating external array data to an Array, and if passed will throw.

It's possible is to specify the type of external array data you would like. All possible options are listed in smalloc.Types. Example usage:

var doubleArr = smalloc.alloc(3, smalloc.Types.Double);

for (var i = 0; i < 3; i++)
  doubleArr = i / 10;

// { '0': 0, '1': 0.1, '2': 0.2 }

It is not possible to freeze, seal and prevent extensions of objects with external data using Object.freeze, Object.seal and Object.preventExtensions respectively.

smalloc.copyOnto(source, sourceStart, dest, destStart, copyLength);

• source {Object} with external array allocation
• sourceStart {Number} Position to begin copying from
• dest {Object} with external array allocation
• destStart {Number} Position to begin copying onto
• copyLength {Number} Length of copy

Copy memory from one external array allocation to another. No arguments are optional, and any violation will throw.

var a = smalloc.alloc(4);
var b = smalloc.alloc(4);

for (var i = 0; i < 4; i++) {
  a[i] = i;
  b[i] = i * 2;
}

// { '0': 0, '1': 1, '2': 2, '3': 3 }
// { '0': 0, '1': 2, '2': 4, '3': 6 }

smalloc.copyOnto(b, 2, a, 0, 2);

// { '0': 4, '1': 6, '2': 2, '3': 3 }

copyOnto automatically detects the length of the allocation internally, so no need to set any additional properties for this to work.

smalloc.dispose(obj)

• obj Object

Free memory that has been allocated to an object via smalloc.alloc.

var a = {};
smalloc.alloc(3, a);

// { '0': 0, '1': 0, '2': 0 }

smalloc.dispose(a);

// {}

This is useful to reduce strain on the garbage collector, but developers must be careful. Cryptic errors may arise in applications that are difficult to trace.

var a = smalloc.alloc(4);
var b = smalloc.alloc(4);

// perform this somewhere along the line
smalloc.dispose(b);

// now trying to copy some data out
smalloc.copyOnto(b, 2, a, 0, 2);

// now results in:
// RangeError: copy_length > source_length

After dispose() is called object still behaves as one with external data, for example smalloc.hasExternalData() returns true. dispose() does not support Buffers, and will throw if passed.

smalloc.hasExternalData(obj)

• obj {Object}

Returns true if the obj has externally allocated memory.

smalloc.kMaxLength

Size of maximum allocation. This is also applicable to Buffer creation.

smalloc.Types

Enum of possible external array types. Contains:

• Int8
• Uint8
• Int16
• Uint16
• Int32
• Uint32
• Float
• Double
• Uint8Clamped