US 7,003,768 B2Granted

Method and apparatus for class intialization barriers and access to class variables in multitasking virtual machines

AssigneeSun Microsystems, Inc.

InventorsLaurent P. Daynes, Grzegorz J. Czajkowski

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Abstract

One embodiment of the present invention provides a system for efficient class initialization barrier and access to class information private to a task that enables sharing between multiple tasks/virtual machines of both interpreted platform-independent code and the equivalent native code produced at runtime, wherein a class initialization barrier guarantees that a task initializes a class before the class is first used by the program executed by the task. The system operates by associating the shared runtime representation of classes with tables of pointers to task class mirror objects that hold the task private representation of a class. Entries of task class mirror tables are used both as a mean to encode the initialization status of the associated class for a plurality of tasks, and to provide access to the task private representation of a class loaded by a task irrespectively of the initialization state of the class for this task.

Claims42

Dependent claims

A method to efficiently realize class initialization barriers in a multitasking virtual machine, wherein class loading always takes place before class initialization, and wherein a class initialization barrier guarantees that a class is initialized before the class is first used by a program, comprising:

associating a shared runtime representation of the class with a task class mirror table that comprises at least one entry per-task, including an initialized entry, for a plurality of tasks, wherein each entry holds either a null pointer value or a non-null pointer to a task class mirror object, wherein all entries of a task mirror table that hold a non-null pointer value and that are associated with a same task hold a pointer to a same task class mirror object, wherein the task class mirror object holds a task private representation of the class for that task, wherein each task is associated with a unique integer value, wherein the unique integer value is used to compute a byte-offset from a beginning of task class mirror tables that can be used to retrieve from the initialized entry of any task class mirror table the pointer to the task class mirror object, wherein a computed byte-offset to the initialized entry is stored in a descriptor of a plurality of threads executing on behalf of a corresponding task;
using the initialized entry of a task in the task class mirror table to determine whether this task has initialized the class associated with the task class mirror table, which involves:
examining the initialized entry of the task in the task class mirror table associated with the class in order to determine if that task has initialized the class, wherein the byte-offset to the initialized entry from the beginning of the task class mirror table is obtained from the descriptor of a thread performing an examination on behalf of the task;
and
initializing the class by the task if the class is not already initialized, wherein a null pointer stored at the initialized entry indicates that the class has not initialized the task, wherein a non-null pointer value indicates that the class has been initialized;
and
accessing the task class mirror object associated to a particular task.

4 more elements

A computer-readable tangible storage medium storing instructions that when executed by a computer cause the computer to perform a method to efficiently realize class initialization barriers in a multitasking virtual machine, wherein class loading always takes place before class initialization, and wherein a class initialization barrier guarantees that a class is initialized before the class is first used by a program, comprising:

associating a shared runtime representation of the class with a task class mirror table that comprises at least one entry per-task, including an initialized entry, for a plurality of tasks, wherein each entry holds either a null pointer value or a non-null pointer to a task class mirror object, wherein all entries of a task mirror table that hold a non-null pointer value and that are associated with a same task hold a pointer to a same task class mirror object, wherein the task class mirror object holds a task private representation of the class for that task, wherein each task is associated with a unique integer value, wherein the unique integer value is used to compute a byte-offset from a beginning of task class mirror tables that can be used to retrieve from the initialized entry of any task class mirror table the pointer to the task class mirror object, wherein a computed byte-offset to the initialized entry is stored in a descriptor of a plurality of threads executing on behalf of a corresponding task;
using the initialized entry of a task in the task class mirror table to determine whether this task has initialized the class associated with the task class mirror table;
which involves:
examining the initialized entry of the task in the task class mirror table associated with the class in order to determine if that task has initialized the class, wherein the byte-offset to the initialized entry from the beginning of the task class mirror table is obtained front the descriptor of a thread performing an examination on behalf of the task;
and
initializing the class by the task if the class is not already initialized, wherein a null pointer stored at the initialized entry indicates that the class has not initialized the task, wherein a non-null pointer value indicates that the class has been initialized;
and
accessing the task class mirror object associated to a particular task.

5 more elements

An apparatus to efficiently realize class initialization barriers in a multitasking virtual machine, wherein class loading always takes place before class initialization, and wherein a class initialization barrier guarantees that a class is initialized before the class is first used by a program, comprising:

an associating mechanism that is configured to associated a shared runtime representation of the class with a task class mirror table that comprises at least one entry per-task, including an initialized entry, for a plurality of tasks, wherein each entry holds either a null pointer value or a non-null pointer to a task class mirror object, wherein all entries of a task mirror table that hold a non-null pointer value and that are associated with a same task hold a pointer to a same task class mirror object, wherein the task class mirror object holds a task private representation of the class for that task, wherein each task is associated with a unique integer value, wherein the unique integer value is used to compute a byte-offset from a beginning of task class mirror tables that can be used to retrieve from the initialized entry of any task class mirror table the pointer to the task class mirror object, wherein a computed byte-offset to the initialized entry is stored in a descriptor of a plurality of threads executing on behalf of a corresponding task;
a determining mechanism that is configured to use the initialized entry of a task in the task class mirror table to determine whether this task has initialized the class associated with the task class mirror table, which involves:
examining the initialized entry of the task in the task class mirror table associated with the class in order to determine if that task has initialized the class, wherein the byte-offset to the initialized entry from the beginning of the task class mirror table is obtained from the descriptor of a thread performing an examination on behalf of the task;
and
initializing the class by the task if the class is not already initialized, wherein a null Pointer stored at the initialized entry indicates that the class has not initialized the task, wherein a non-null pointer value indicates that the class has been initialized;
and
an accessing mechanism that is configured to access the task class mirror object associated to a particular task.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/975,145Filed 9 Oct 2001 · us provisional application
Priority: 15 Mar 2001
Published: US 2002/0133527 A119 Sep 2002
Granted: 21 Feb 2006
Term ends: Not estimatedThe source records don’t support an estimate.

Classification3 codes

G06F 9/45516
Abstract machines for program code execution, e.g. Java virtual machine [JVM], interpreters or emulators: runtime code conversion or optimisation
G06F 9/445
Arrangements for executing specific programs: program loading or initiating
G06F
Computing and data processing