Reduced size objects headers
A method and apparatus for reducing memory requirements in a computing environment. The method includes reducing the size of a header for a data structure by creating a header consisting of index information. Alternatively, the header may also include garbage collection information. The invention also provides a data structure for an object-oriented programming environment. The data structure includes: 1) a header consisting of index information and 2) one or more fields. Unlike prior data structures the header does not include information regarding the data structure's size; where it references are; it dispatch table; hash code information; or monitor information.
1. A computing environment, comprising:
a plurality of objects each having a header with header address information therein and corresponding object class information, object size information and monitor information located outside the plurality of objects;
the headers having 32 or fewer bits of header information including only garbage collection information and header index information, wherein the garbage collection information is stored in a predefined number N of bits of the headers and the header index information is stored in the remaining 32−N or fewer bits of the headers;
header index to class information pointers for the plurality of objects to permit accessing the object class information in accordance with the index information;
a first data structure for storing and providing a global index of the header index to class information pointers wherein the index information of a selected header within a selected object provides a global index address of 32−N or fewer bits for addressing a header index to class information pointer to provide a referenced header index to class information pointer;
a second data structure separate from the first data structure for providing a dispatch table having slots for storing class pointers wherein a selected class pointer is addressed by the referenced header index to class information pointer to provide a referenced class pointer,
the referenced class pointer indicating a location in a third data structure separate from the first and second data structures containing the corresponding object class information of the selected object whereby the corresponding object class information of the selected object is indirectly addressed by the 32−N or fewer bits of the header within the object by way of the global index and by way of the dispatch table; and
a fourth data structure for storing the header address information of the plurality of objects wherein the monitor information of the selected object in obtained in accordance with a match between a hash code representation of the address of the selected header and the header address information within said fourth data structure.
2. A computing environment as claimed in claim 1 , further comprising a table of garbage collection information mapped to the object.
3. A computing environment as claimed in claim 1 , wherein the global index is addressed with an address equal to the size of the header.