Oracle America, Inc.

Sun Microsystems, Inc.

Oracle International Corporation

Antonios Printezis

David L Detlefs

Paul Henry Hohensee

Alexander T Garthwaite

Igor Veresov

John Coomes

Fabio Rojas

David Dice

Peter B Kessler

Staffan Friberg

Y Srinivas Ramakrishna

Charlie Hunt

John W Coomes

Mark S Moir

Nir N Shavit

Brian Goetz

Steven K Heller

David P Stoutamire

Yin Zin Mark Lam

Jon A Masamitsu

M Bertrand Delsart

Y Srinivas Ramakrisha

Methods and systems for garbage collection are described. In some embodiments, Garbage collector threads may maximize local accesses and minimize remote access by copying Young objects and Old objects differently. When copying a Young object, a garbage collector thread may determine the lgroup of the pool that contains the object and copy the object to a pool of the same lgroup. The garbage collector thread may spread Old objects among lgroups by copying Old objects to pools of the same lgroup as the respective garbage collector thread. Additional methods and systems are disclosed.

NUMA-aware garbage collection

System and Methods for non-uniform memory (NUMA) garbage collection are provided. Multiple memories and processors are categorized into local groups. A heap space is divided into multiple pools and stored in each of the memories. Garbage collection threads are assigned to each of the local groups. Garbage collection is performed using the garbage collection threads for objects contained in the pools using the garbage collector threads, memory, and processor assigned to each local group, minimizing remote memory accesses.

A processing thread obtains an initial status of a reference field associated with an object having data stored in memory. The reference field represents, at least in part, a status of current modification operations (e.g., a status of moving the object from one location in memory to another), if any, applied to the object. The processing thread applies a sequence of instructions to data retrieved from the object to produce computational results for storage in the object. Prior to storing the computational results in the object, the processing thread can confirm whether the reference field has changed since obtaining the initial status.

Concurrent object management

A method for queuing thread update buffers to enhance garbage collection. The method includes providing a global update buffer queue and a global array with slots for storing pointers to filled update buffers. The method includes with an application thread writing to the update buffer and, when filled, attempting to write the pointer for the update buffer to the global array. The array slot may be selected randomly or by use of a hash function. When the writing fails due to a non-null slot, the method includes operating the application thread to add the filled update buffer to the global update buffer queue. The method includes, with a garbage collector thread, inspecting the global array for non-null entries and, upon locating a pointer, claiming the filled update buffer. The method includes using the garbage collector thread to claim and process buffers added to the global update buffer queue.

Low-contention update buffer queuing for large systems

Improvements to apparatus, methods, and computer program products are disclosed to improve the efficiency of pinning objects in a heap memory that is subject to a garbage collection system.

Efficient object pinning in a multi-threaded environment

System and Methods for time based object aging for generational garbage collectors are provided. Time data is received from a user identifying the amount of time an object should survive in a generation defined in a heap. Generational garbage collection is performed, and objects are promoted from one generation to the next oldest generation based on the time data received.

Time-based object aging for generational garbage collectors

A method, apparatus and computer program product for providing page-protection based memory access barrier traps is presented. A value for a user-mode bit (u-bit) is computed for each extant virtual page in an address space, the u-bit indicative that an object on the virtual page is being moved by a Garbage Collector process. An instruction is executed which causes an access protection fault. The state of the u-bit for the virtual page associated with the access protection fault is consulted when the access protection fault is encountered. Additionally, the access protection fault is translated into a user-trap (utrap) and the utrap is serviced when the u-bit is set.

Page-protection based memory access barrier traps

A method for queuing update buffers to enhance garbage collection. The method includes running an application thread and providing, for the application thread, a data structure including current and finished update buffer slots. The method includes providing an update buffer for the application thread and storing a pointer to the update buffer in the current update buffer slot. The method includes storing null in the finished update buffer slot and, with the application thread, writing to the update buffer. The thread may write a pointer to the filled update buffer in the finished update buffer slot after the buffer is filled. The method includes using a garbage collector thread to inspect the finished update buffer slot and claim filled buffers and change the pointer to null. The thread then obtains an empty update buffer and updates the current update buffer slot to point to the new buffer.

Low-contention update buffer queuing for small systems

The present disclosure describes garbage collection that provides prompt reclamation of large objects. A heap space is divided into Young regions, Old regions, and Humongous regions. A remembered set is created and maintained, during the execution of one or more programs, for each region that specifies where there are references from outside the region to inside the region. A garbage collection list is generated specifying regions to perform garbage collection on. All Young regions and at least one Humongous region are included in the garbage collection list. If it is determined to include Old regions, the Old regions are selected and included in the garbage collection list. Then, a garbage collection is performed on the regions specified in the garbage collection list. During the garbage collection, the indication for each region is utilized to determine reachable objects in the region, ensuring that reachable objects are not deallocated.

Prompt large object reclamation

One embodiment of the present invention provides a system that uses observed object patterns to dynamically tune a virtual machine for responsiveness and/or throughput. The system first analyzes a memory region containing a set of objects to identify objects in the memory region that indicate the need for responsiveness and/or throughput. The system gathers statistics based on the identified and unidentified objects in the set of objects, and then uses these statistics to dynamically tune a virtual machine.

Using observed object patterns to dynamically tune a virtual machine for responsiveness

System and Methods for time-based object aging for generational garbage collectors are provided. Time data is received from a user identifying the amount of time an object should survive in a generation defined in a heap. A circular buffer is generated to store a plurality of starting time for a plurality of garbage collections. Generational garbage collection is performed, and the time data in conjunction with the starting times stored in the circular buffer are used to determine when objects are promoted from one generation to the next oldest generation.

A garbage collector determines a target amount of heap space to deallocate, estimates an amount of heap space reachable by a plurality of soft references by determining a cumulative size of no more than an exploration bound N number of objects reachable from each soft reference, and deallocates heap space based on the target amount and the estimate of the heap space reachable from the soft references. Deallocating heap space may include clearing at least one soft reference. If the estimate is inaccurate, it may be utilized regardless or modified to account for inaccuracy. The least-recently-used or the largest soft reference may be cleared until the total cleared space reachable exceeds the target amount. By performing a bounded analysis, the garbage collector may be able to make a more informed decision about whether to clear a soft reference without consuming the full amount of resources consumed by an exhaustive analysis.

Growing community of inventors

Burlington, MA, United States of America

Antonios Printezis