Synchronizing Communication Over Shared Memory

• US 20090328059A1
• Filed: 06/27/2008
• Published: 12/31/2009
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Haba, Erez
• Granted Patent: US 8,555,292 B2
• Time in Patent Office: Days
• US Class Current: 719/312
• CPC Class Codes: G06F 9/544 Buffers; Shared memory; Pipes

Abstract

Two threads may communicate via shared memory using two different modes. In a polling mode, a receiving thread may poll an indicator set by the sending thread to determine if a message is present. In a blocking mode, the receiving thread may wait until a synchronization object is set by the sending thread which may cause the receiving thread to return to the polling mode. The polling mode may have low latency buy may use processor activity of the receiving thread to repetitively check the indictor. The blocking mode may have a higher latency but may allow the receiving thread to enter a sleep mode or perform other activities.

Claims

1. A method of communicating between a sender thread and a receiving thread through shared memory, the method comprising:

sending a first message by said sender thread by a polling transmission method comprising;

storing said first message; and

changing a transmit index;

receiving said first message by said receiving thread by a polling receiving method comprising;

reading said transmit index to determine that said first message is ready to be read; and

reading said first message;

changing to a synchronization object receiving method by said receiving thread by a first changeover method comprising;

setting a wait object;

transmitting a second message by said sender thread by a synchronization object transmission method comprising;

detecting that said wait object is set;

setting an awake object;

storing said second message; and

changing said transmit index; and

changing from a synchronization object receiving method by said receiving thread to said polling transmission method by a second changeover method comprising;

receiving said awake object; and

executing said polling receiving method.

2. The method of claim 1, said changing said transmit index comprising toggling said transmit index.

3. The method of claim 1, said changing said transmit index comprising incrementing said transmit index.

4. The method of claim 3, said transmit index comprising a first pointer to a buffer.

5. The method of claim 4, said polling transmission method further comprising:

storing a second pointer in said buffer, said second pointer comprising an address to said first message.

6. The method of claim 4, said buffer being a circular buffer.

7. The method of claim 1, said polling receiving method further comprising:

comparing said transmit index to a receive index to determine said first message is ready to be read.

8. The method of claim 7, said polling receiving method further comprising:

incrementing said receive index after said reading said first message from said shared memory.

9. The method of claim 1, said first changeover method further comprising:

determining that no new messages are available.

10. The method of claim 9, said first changeover method further comprising:

forcing a purge of a first memory pipeline for said receive thread prior to said setting said wait object.

11. The method of claim 10, said polling transmission method further comprising:

forcing a purge of a second memory pipeline for said sender thread after said changing said transmit index.

12. A system comprising:

a first thread;

a second thread;

a shared memory capable of being accessed by said first thread and said second thread;

one of said first thread and said second thread being a sending thread and the other of said first thread and said second thread being a receiving thread, said sending thread and said receiving thread being configured to communicate using a method comprising;

sending a first message by said sender thread by a polling transmission method comprising;

storing said first message in said shared memory; and

changing a transmit index;

receiving said first message by said receiving thread by a polling receiving method comprising;

reading said transmit index to determine that said first message is ready to be read; and

reading said first message from said shared memory;

changing to a synchronization object receiving method by said receiving thread by a first changeover method comprising;

setting a wait object;

transmitting a second message by said sender thread by a synchronization object transmission method comprising;

detecting that said wait object is set;

setting an awake object;

storing said second message in said shared memory; and

changing said transmit index; and

changing from a synchronization object receiving method by said receiving thread to said polling transmission method by a second changeover method comprising;

receiving said awake object; and

executing said polling receiving method.

13. The system of claim 12, said first thread being said sending thread and said second thread being said receiving thread.

14. The system of claim 13, said second thread being configurable as said sending thread and said first thread being configurable as said receiving thread.

15. The system of claim 12, said changing said transmit index comprising incrementing said transmit index.

16. The system of claim 15, said transmit index comprising a first pointer to a buffer.

17. The system of claim 16, said polling transmission method further comprising:

storing a second pointer in said buffer, said second pointer comprising an address to said first message.

18. The system of claim 17, said buffer being a circular buffer.

19. A method of communicating between a sender thread and a receiving thread through shared memory, the method comprising:

sending a first message by said sender thread by a polling transmission method comprising;

storing said first message in said shared memory;

storing a pointer to said first message in a first register of a first buffer;

changing a transmit index to indicate said first register of said first buffer; and

purging a memory pipeline of said sender processor;

receiving said first message by said receiving thread by a polling receiving method comprising;

reading said transmit index;

reading a receive index;

comparing said transmit index to said receive index to determine that said transmit index and said receive index are different;

incrementing said receive index;

reading said first register from said first buffer, said first register corresponding to said receive index; and

reading said first message from said shared memory;

changing to a synchronization object receiving method by said receiving thread by a first changeover method comprising;

setting a wait object;

transmitting a second message by said sender thread by a synchronization object transmission method comprising;

detecting that said wait object is set;

setting an awake object;

storing said second message in said shared memory; and

changing said transmit index; and

changing from a synchronization object receiving method by said receiving thread to said polling transmission method by a second changeover method comprising;

receiving said awake object; and

executing said polling receiving method.

20. The method of claim 19, said first changeover method further comprising:

purging a second memory pipeline after said setting said wait object.