Zero-copy transfer of memory between address spaces

• US 20060259571A1
• 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: Talluri, Madhusudhan, Sivathanu, Muthian
• Granted Patent: US 7,454,477 B2
• Time in Patent Office: Days
• US Class Current: 709/213
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

Methods for performing zero-copy memory transfers between processes or services using shared memory without the overhead of current schemes. An IPC move semantic may be used that allows a sender to combine passing a reference and releasing it within the same IPC call. An insulate method removes all references to the original object and creates a new object pointing to the original memory if a receiver requires exclusive access. Alternatively, if a receiving process or service seeks read-only access, the sender unmaps its access to the buffer before sending to the receiver. When the insulate operation is initiated, the kernel detects an object with multiple active references but no active mappings and provides a mapping to the memory without taking a copy or copy-on-write.

Claims

1. A method of transferring data between services using shared memory, comprising:

controlling sharing of a memory object;

determining if outstanding handles to said memory object exist; and

if said outstanding handles do not exist, transferring a pointer to said memory object from a first service to a second service to avoid making a copy of said memory object.

2. The method of claim 1, further comprising providing a first operation, which logically creates a new copy of said memory object.

3. The method of claim 1, further comprising providing a second operation that revokes all said outstanding handles to said memory object.

4. The method of claim 3, further comprising creating a new memory object that points to a same memory location that said memory object pointed to.

5. The method of claim 1, further comprising:

releasing a reference to said memory object as said first service passes said pointer to said second service; and

ensuring that there are no other references to said memory object.

6. The method of claim 1, further comprising:

delaying making a copy of said memory object while said outstanding handles exist but there are no active mappings; and

alternating read/write mappings to said memory object between said first service and second service such that neither said first service, nor said second service have a write mapping to said memory object at the same time.

7. The method of claim 6, further comprising making a copy when said second service establishes a write mapping to said memory object and said first service attempts to establish a write mapping to said memory object.

8. A computer readable medium having stored thereon computer executable instructions for transferring data between services using shared memory, said instructions for performing the method of:

controlling sharing of a memory object;

determining if outstanding handles to said memory object exist; and

if said outstanding handles do not exist, transferring a pointer to said memory object from a first service to a second service to avoid making a copy of said memory object.

9. The computer readable medium of claim 8, further comprising instructions for providing a first operation, which logically creates a new copy of said memory object.

10. The computer readable medium of claim 8, further comprising instructions for providing a second operation that revokes all said outstanding handles to said memory object.

11. The computer readable medium of claim 10, further comprising instructions for creating a new memory object that points to a same memory location that said memory object pointed to.

12. The computer readable medium of claim 8, further comprising instructions for:

releasing a reference to said memory object as said first service passes said pointer to said second service; and

ensuring that there are no other references to said memory object.

13. The computer readable medium of claim 8, further comprising instructions for:

delaying making a copy of said memory object while said outstanding handles exist but there are no active mappings; and

alternating read/write mappings to said memory object between said first service and second service such that neither said first service, nor said second service have a write mapping to said memory object at the same time.

14. The computer readable medium of claim 13, further comprising instructions for making a copy when said second service establishes a write mapping to said memory object and said first service attempts to establish a write mapping to said memory object.

15. A method of transferring data between a first service and a second service, comprising:

creating a first memory object pointing to a buffer for use by said first service;

writing to said buffer;

releasing said buffer;

removing references to said buffer; and

creating a second memory object pointing to said buffer for use by said second service without creating a copy of said buffer.

16. The method of claim 15, further comprising sharing said buffer between said first service and said second service.

17. The method of claim 16, further comprising alternating read/write mappings to said buffer such that neither said first service, nor said second service have a write mapping to said buffer at the same time.

18. The method of claim 17 further comprising delaying making a copy of said memory object while said outstanding handles exist but there are no active mappings.

19. The method of claim 18, further comprising making a copy when said second service establishes a write mapping to said memory object and said first service attempts to establish a write mapping to said memory object.

20. The method of claim 16, further comprising making a copy only when one of the services attempts to write to said buffer while the other service has a write mapping to said buffer.