International Business Machines Corporation

Filip Jeremic

Aleksandar Micic

Joran S C Siu

Irwin D'Souza

Evgenia Badiyanova

Vijay Sundaresan

Andrew James Craik

Charles Robert Gracie

Dmitri Pivkine

A value profiling method, system and computer program product that leverages a guarded storage facility. During code execution, a first instruction is loaded. The first instruction has a first value designating a first region of memory and the first instruction is related to a first section of the code. A determination is made as to whether a guarded mode is enabled at the first region. Responsive to an enabled guarded mode at the first region, a secondary operation is triggered. The secondary operation is in addition to a primary operation of the first instruction. The primary operation is relative to the first region of the memory. The secondary operation causes a profiling of the first section of the code.

Software-directed value profiling with hardware-based guarded storage facility

Systems and methods for object load introspection using guarded storage are disclosed. In embodiments, a computer-implemented method includes: determining objects of interest designated by a user; splitting a first subset of a predetermined memory heap into guarded regions based on a number of objects of interest; allocating each of the objects of interest to a respective one of the guarded regions and remaining objects to a second subset of the predetermined memory heap; executing a program; detecting one of the objects of interest is loaded from one of the guarded regions; generating a trap that transfers control of the executing the program to a signal handler, wherein the signal handler is designated to perform a user-defined task associated with the one of the objects of interest; and executing, by the signal handler of the computing device, the user-defined task.

Object load introspection using guarded storage

An approach for optimizing a copying of a data object in a concurrent copying garbage collection operation is provided. In an embodiment, a source copy of the data object to be copied as part of the garbage collection operation is identified. A copying of the source copy to a target location is initiated by a primary accessing thread. This initiating of the copying includes the creation of a temporary target object header for the target object in the target location that contains an indicator set to indicate that the copying is ongoing. As the copying is occurring, the execution of any other accessing threads that are attempting to use the data object are held for as long as the indicator indicates that the copying is ongoing. Once the copying has completed, the target object header is replaced with a copy of the source object header, resetting the indicator.

Copying and forwarding for concurrent copying garbage collection

Multi-byte compressed string representation embodiments define a String class control field identifying compression as enabled/disabled, and another control field, identifying a decompressed string created when compression enabled. Tests are noped based on null setting of the compression flag. When arguments to a String class constructor are not compressible, a decompressed String is created and stringCompressionFlag initialized. Endian-aware helper methods for reading/writing byte and character values are defined. Enhanced String class constructors, when characters are not compressible, create a decompressed String, and initialize stringCompressionFlag triggering class load assumptions, overwriting all nopable patch points. A String object sign bit is set to one for decompressed strings when compression enabled, and masking/testing this flag bit is noped. Alternative package protected string constructors and operations are provided. A predetermined location is checked to determine whether supplied arguments to a String class constructor are compressible is performed.

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Hamilton, Canada

Filip Jeremic