A computer system stores a dynamically sized array as a base array that
contains references to subarrays in which the (composite) array's data
elements reside. Each of the base-array elements that thus refers to a
respective subarray is associated with a respective subarray size. Each
base-array index is thereby at least implicitly associated with a
cumulative base value equal to the sum of all preceding base indexes'
associated subarray sizes. In response to a request for access to the
element associated with a given (composite-array) index, the array-access
system identifies the base index associated with the highest cumulative
base value not greater than the composite-array index and performs the
access to the subarray identified by the element associated with that
base index. Composite-array expansion can be performed in a
multi-threaded environment without locking, simply by employing a
compare-and-swap or similar atomic operation.