Module Portable_common.Padding

Depending on the object, either creates a shallow clone of it or returns it as is. When cloned, the clone will have extra padding words added after the last used word.

This is designed to help avoid false sharing. False sharing has a negative impact on multicore performance. Accesses of both atomic and non-atomic locations, whether read-only or read-write, may suffer from false sharing.

The intended use case for this is to pad all long lived objects that are being accessed highly frequently (read or written).

Many kinds of objects can be padded, for example:

  let padded_atomic = Padding.copy_as_padded (Atomic.make 101)
  let padded_ref = Padding.copy_as_padded (ref 42)
  let padded_record = Padding.copy_as_padded { number = 76; pointer = [ 1; 2; 3 ] }
  let padded_variant = Padding.copy_as_padded (Some 1)

Padding changes the length of an array. If you need to pad an array, use make_padded_array.

copy_as x by default simply returns x. When ~padded:true is explicitly specified, returns copy_as_padded x.

Creates a padded array. The length of the returned array includes padding. Use length_of_padded_array to get the unpadded length.

Returns the length of an array created by make_padded_array without the padding.

WARNING: This is not guaranteed to work with copy_as_padded.

Returns the length of an array created by make_padded_array without the padding minus 1.

WARNING: This is not guaranteed to work with copy_as_padded.