Bounded-pause time garbage collection system and method including read and write barriers associated with an instance of a partially relocated object

An apparatus comprising:

• memory storage, wherein objects formed therein are relocatable from respective FromSpace instances to respective ToSpace instances thereof;
• a partially relocated object identifier store updatable to identify a FromSpace instance of a particular one of said objects, if any, for which relocation is incomplete;
• and
• a write barrier to a store-oriented memory access targeting said FromSpace instance;
• and
• a read barrier to a load-oriented memory access targeting said FromSpace instance, wherein, at least during a pointer update phase of said relocation, said read barrier directs said load-oriented memory access to a ToSpace instance of said particular object.

An apparatus comprising:

• memory storage, wherein objects formed therein are relocatable from respective FromSpace instances to respective ToSpace instances thereof;
• a partially relocated object identifier store updatable to identify a ToSpace instance of a particular one of said objects, if any, for which relocation is incomplete;
• a write barrier to store-oriented memory accesses targeting said ToSpace instance;
• and
• a read barrier to load-oriented memory accesses targeting said ToSpace instance.

A garbage collection system to manage memory object instance consistency during relocation of a particular memory object in a computer system providing bounded pause-time relocation of said particular memory object using incremental copying of said particular object from a first instance to a second instance thereof, said garbage collection system comprising:

• a partially relocated object identifier store including identifier fields for said first and said second instances;
• write barrier logic responsive to a correspondence between an object identifier for a store-oriented mutator process access and contents of said first instance identifier field;
• and
• read barrier logic responsive to a correspondence between an object identifier for a load-oriented mutator process access and contents of said first instance identifier field.

A method for bounding garbage collection pause time, said method comprising:

• during relocating of a memory object from a source instance to a target instance thereof, interrupting said relocating in accordance with a bounded pause time commitment to a mutator process;
• during said interrupting of said relocating, detecting a correspondence between an object identifier for a write access by said mutator process and contents of a partially relocated object identifier store;
• selectively directing, based on a partial relocation state of said memory object, said write access to one of said source instance and said target instance;
• during said interrupting of said relocating, detecting a correspondence between an object identifier for a read access by said mutator process and contents of a partially relocated object identifier store;
• selectively directing, based on said partial relocation state of said memory object, said read access to one of said source instance and said target instance.

A method for relocating a memory object with bounded pause time impact on a mutator process having access thereto, said method comprising:

• configuring write and read barriers to respond to respective store-oriented and load-oriented accesses by said mutator process targeting a From instance of said memory object;
• incrementally copying said memory object from said From instance to a To instance and incrementally updating pointers thereto;
• during said incremental copying and pointer updating, and in response to a first of said store-oriented accesses, directing said first store-oriented access targeting a copied portion of said memory object to said To instance thereof;
• during said incremental copying and pointer updating, and in response to a first of said load-oriented accesses, directing said first load-oriented access targeting said copied portion of said memory object to said To instance thereof.

A method for relocating a memory object with bounded pause time impact on a mutator process having access thereto, said method comprising:

• configuring write and read barriers to respond to respective store-oriented and load-oriented accesses by said mutator process targeting a To instance of said memory object;
• incrementally updating pointers referencing said From instance to instead reference a To instance and incrementally copying said memory object from said From instance to said To instance;
• during said incremental pointer updating and copying, and in response to a first of said store-oriented accesses, directing said first store-oriented access targeting an uncopied portion of said memory object to said From instance thereof,
• during said incremental pointer updating and copying, and in response to a first of said load-oriented accesses, directing said first load-oriented access targeting said uncopied portion of said memory object to said From instance thereof.

A method comprising:

• maintaining a partial relocation state including a FROM instance identifier state, a TO instance identifier state, and a partial copy position indicating state in accordance with incremental copying of a memory object and incremental updating of pointers thereto;
• (a) selectively directing, using a hardware read barrier responsive to said partial relocation state, load-oriented memory accesses to either a FROM instance or a TO instance of said memory object;
• and
• (b) selectively directing, using a hardware write barrier responsive to said partial relocation state, store-oriented memory accesses to either a FROM instance or a TO instance of said memory object,
• said (a) and said (b) selective directing maintaining a consistent object representation for a mutator process making said load-oriented and said store-oriented memory accesses.

A computing machine comprising:

• a processor;
• memory, wherein objects formed therein are referenceable by said processor;
• and
• means accessible by said processor for identifying a partially collected object in said memory, wherein a correspondence between said partially collected object identifier means and an object identifier for an object reference operation by said processor triggers fault handler means;
• means for garbage collecting said memory, wherein said garbage collecting means maintains said partially collected object identifier means to identify a particular one, if any, of said objects for which garbage collection is incomplete, thereby allowing interruption of said garbage collecting means in accordance with a bounded pause time commitment to mutator means executable on said processor.