Coordinating reference counting between entities executing within separate address spaces

• US 20060259489A1
• Filed: 05/16/2005
• Published: 11/16/2006
• Est. Priority Date: 05/16/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Khalidi, Yousef A., Bernabeu-Auban, Jose M., Havens, Jeff L.
• Granted Patent: US 7,581,232 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 2209/463 Naming
• CPC Class Codes: G06F 9/465 Distributed object oriented systems remote method invocation [RMI] G06F9/548
• CPC Class Codes: G06F 9/5016 the resource being the memory
• CPC Class Codes: G06F 9/5022 Mechanisms to release resources

Abstract

Reference counting is shared between an in-process service runtime and a machine-wide service. The machine-wide service maintains a count for the total number of references to an object or resource (the global reference count), a count for the number of exports of a object (the global export count) and a count of the number of exports that must be received by the machine-wide service before a revoke can occur (the exports before revoke count). When a process exports an object or resource, the machine-wide service increments the global export count for the object or resource and increments the global reference count for the object or resource. The machine-wide service increments the global reference count for a passed reference but does not increment the global reference count. The machine-wide service decrements the global reference count in response to receiving an unreferenced message. When the global reference count for a resource or object drops to zero, the machine-wide service deletes the table entry for the object or resource and sends an unref message including the value of the global export count to the sharing process. If the local export count is greater than the global export count of the unref, there are committed exports which have not yet been unreferenced. If both counts are the same, the committed exports have been accounted for and a revoke operation can be issued.

Claims

1. An inter-process communication system comprising:

a trusted entity that maintains a global export count representing a quantity of references to a resource exported by a sharing process, a global reference count representing a quantity of outstanding references to the resource in the inter-process communication system and a count representing a quantity of exports of the resource that must be received before a revoke operation can be initiated.

2. The system of claim 1, further comprising a table associated with the sharing process, the table comprising the global export count, the global reference count and the count representing the quantity of exports of the resource that must be received before the revoke operation can be initiated.

3. The system of claim 1, wherein the global export count is incremented when the sharing process exports a reference to the resource.

4. The system of claim 1, wherein the global reference count is incremented when the sharing process exports a reference to the resource.

5. The system of claim 1, wherein the global reference count is incremented when a process receiving a reference to an exported resource passes the reference to the exported resource to another process.

6. The system of claim 1, wherein an unreferenced message is generated in response to the global reference count dropping to zero.

7. The system of claim 6, wherein the global export count is passed with the unreferenced message.

8. The system of claim 1, wherein a revoke operation is initiated when the count representing the quantity of exports of the object that must be received before the revoke operation can be initiated is equal to the global export count.

9. A method for coordinating reference counting comprising:

receiving a message from a process that has received a reference to an object; and

in response to determining that the message is a message indicating that the process is finished with the object reference, deleting an entry for the object in a table for the process and decrementing a global reference count, the global reference count comprising a total of references to the object.

10. The method of claim 9, further comprising, in response to determining that the global reference count is zero, sending a message indicating that there are no more object references to the object to a process that shared the object.

11. The method of claim 10, wherein the message sent to the process that shared the object includes a global export count comprising a count of a number of times the object was exported to another process.

12. The method of claim 9, wherein in response to receiving a revoke message from a sharing process, the sharing process comprising a process that exported a reference to an object owned by the process to the receiving process, the revoke message including a count of a number of times the object was exported, a comparison is made of the count included with the revoke message and a count of exported references to the object stored in a table for the sharing process.

13. A computer-readable medium comprising computer-executable instructions for coordinating reference counting between a machine-wide reference counting mechanism and a process within a inter-process communication system, comprising instructions for:

receiving a message from a sharing process in the inter-process communication system, the sharing process comprising a process that passes a reference to a resource owned by the process to a receiving process, the message comprising a notification that a resource is to be exported from the sharing process to the receiving process, and in response incrementing a global reference count for the resource in a table maintained by the machine-wide reference counting mechanism for the sharing process and incrementing a global export count for the resource in the table, the global export count representing a number of times the sharing process exported the resource.

14. The computer-readable medium of claim 13, comprising further instructions for:

generating a table entry for the resource reference in a table maintained by the machine-wide reference counting mechanism for the receiving process.

15. The computer-readable medium of claim 14, comprising further instructions for:

receiving a message from the receiving process indicating that the resource reference is no longer required and in response decrementing the global reference count and deleting the table entry for the resource reference in the table maintained by the machine-wide reference counting mechanism for the receiving process.

16. The computer-readable medium of claim 15, comprising further instructions for:

in response to determining that the global reference count is zero, sending a message indicating that there are no more references to the resource to the sharing process.

17. The computer-readable medium of claim 14, wherein in response to determining that the receiving process passed the resource reference to a second receiving process, incrementing the global reference count for the resource and failing to increment the global export count.