A talk on interprocess communications with the Java programming language. It also talks about the CLIP library which offers new IPC primitives and simplified access to existing primitives. This was given at the 3/3/2009 Denver Open Source Users Group

1. Java IPC
And the CLIP Library
Clark N. Hobbie
Long Term Software, LLC
clark.hobbie@ltsllc.com

2. Who Gives a Damn?

3. You Should Care Because…
• If you are in a corner
• Java sync is one VM only
• Others require JNI
• Platform differences
3/3/2009 http://ltsllc.com/slides/ipc.html 3

4. What Are the Options?
• Sockets
• Message Queues
• Semaphores
• Shared Memory
3/3/2009 http://ltsllc.com/slides/ipc.html 4

5. Which Option Should I Use?
Shared Memory
• JRE support
• Highest bandwidth
• Decent synchronization
• Naming support
3/3/2009 http://ltsllc.com/slides/ipc.html 5

6. Why Should I Care about CLIP?
• New primitives
– Semaphores
– Message Queues
• Simplifies existing primitives
– Shared Memory
3/3/2009 http://ltsllc.com/slides/ipc.html 6

7. Java
RandomAccessFile raf = new RandomAccessFile(quot;/temp/smfilequot;, quot;rwquot;);
FileChannel chan = raf.getChannel();
MappedByteBuffer buf = chan.map(MapMode.READ_WRITE, 0, size);
byte[] other = new byte[1024];
buf.position(0);
buf.get(other, 0, 1024);
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8. CLIP
SharedMemory smem =
new SharedMemory(quot;/temp/smfilequot;);
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9. What is IPC?
Inter-Process Communication (IPC)
• Multiple processes
• Naming
• Synchronization
• Bandwidth
3/3/2009 http://ltsllc.com/slides/ipc.html 9

10. Naming
Me Tarzan,
who you?
3/3/2009 http://ltsllc.com/slides/ipc.html 10

11. Naming
How do you…
• Connect processes together?
• Determine who is allowed to connect?
• Examples
– TCP/IP?
– Email?
– Telephones?
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12. File Naming
Many IPC methods use the file system
because
• Visible to all processes
• Has access control built in
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13. File Naming Examples
• Memory Mapped Files
• Named Pipes/FIFOs
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14. Synchronization
• Event ordering
• Mutual exclusion
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15. Example: Online Purchase
1. Get user credit information
2. Decision purchase
3. Update credit information
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16. Without Event Ordering
Client A Client B
1 Get credit info
2 Get credit info
2 Decision purchase
3 Update info
4 Decision purchase
5 Update info
3/3/2009 http://ltsllc.com/slides/ipc.html 16

17. With Event Ordering
Client A Client B
1 Get credit info
2 Wait for A
2 Decision purchase
3 Update info
4 Get credit info
5 Decision purchase
6 Update info
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18. Synchronization is Event Ordering
Instead of this order: We want this order:
• A gets credit info • A gets credit info
• B gets credit info • A decisions purchase
• A decisions purchase • A updates info
• A updates info • B gets credit info
• B decisions purchase • B decisions purchase
• B updates credit info • B updates credit info
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19. Which Type of IPC is Appropriate?
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20. IPC Types
• Shared Memory
• Semaphores
• Sockets
• Message Queues
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21. Shared Memory
3/3/2009 http://ltsllc.com/slides/ipc.html 21

22. Shared Memory
• Preferred approach
• Any to any
• get/put semantics
• Synchronization support
• JRE support
• Naming support
3/3/2009 http://ltsllc.com/slides/ipc.html 22

23. Shared Memory Details
• Synchronization
– File Locking
– Lock/unlock ~ 25 usec
• Naming
– File naming
• Bandwidth
– Synchronized 250MB/sec
– Unsynchronized 1000MB/sec
3/3/2009 http://ltsllc.com/slides/ipc.html 23

24. Memory Mapped Files
• Start with a file
– Appears the same to everyone
– Reads/writes appear to everyone
• Now speed it up
– Until its as fast as memory
– Like having the OS buffer
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25. Why Dear God, Why?!!
• Originally Unix
– Where everything is a file
– mmap system call
– CreateFileMapping system call
• Solves the naming problem
• Solves the access problem
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26. Example: World of Warcraft!
Shared Memory!
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27. WoW: Requirements
• One client process per player
• One server process for all
• Server periodically reads all orders
• Server issues results
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28. WoW: Design
Client
Orders
(EvilOne)
Player Order
EvilOne kill
Client Lancelot kill
(Lancelot) Client
Martha Stewart kill
(Conan)
Conan make cookies
…
Client
(Martha)
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29. WoW: Design
Results
Orders
Server
Process Player Result
Player Order
EvilOne dead
EvilOne kill
Lancelot
Lancelot dead
kill
Martha Stewart
Martha Stewart dead
kill
Conan overweight
Conan make cookies
…
…
3/3/2009 http://ltsllc.com/slides/ipc.html 29

30. Shared Memory: Summary
• Preferred IPC
• 250 to 1000MB/sec
• File naming
• Synchronization through file locking
• JRE support
3/3/2009 http://ltsllc.com/slides/ipc.html 30

31. Sockets
3/3/2009 http://ltsllc.com/slides/ipc.html 31

32. Sockets
• TCP/IP
• Point to point
• Stream oriented
• Client/Server
• Synchronized
• Java support
• Naming support
3/3/2009 http://ltsllc.com/slides/ipc.html 32

33. Sockets Details
• Naming
– 127.0.0.1 port 7777
• Synchronization
– Accept, read, write
– 70 usec
• Bandwidth
– 15 MB/sec
3/3/2009 http://ltsllc.com/slides/ipc.html 33

34. Sockets: CLIP
• Some utility classes
– ThreadedSocketServer
• JRE already has excellent support
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35. Example: Google Maps
Copyright © Google
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36. GMaps
Combining Data
Streets
Image
Overlay
Images are Copyright ©
www.Google.com
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37. GMaps: Requirements
• C legacy code
• One instance/process
• Receive file name
• Process for 1 to 10 sec
• Respond with new file name
3/3/2009 http://ltsllc.com/slides/ipc.html 37

38. GMaps: Design
Worker Pool
Server Process
Java VM
Client Client
Client Client
Client Client
Client Client
Client Client
Client Worker
Thread Process
TCP/IP
3/3/2009 http://ltsllc.com/slides/ipc.html 38

39. Sockets vs Shared Memory
• Faster synchronization
– 25 usec vs. 70 usec
• More bandwidth
– 250 MB/sec vs. 15 MB/sec
3/3/2009 http://ltsllc.com/slides/ipc.html 39

40. Message Queues
3/3/2009 http://ltsllc.com/slides/ipc.html 40

41. Message Queues
• Point to point
• Message or stream
• Client/Server
• Synchronization support
• No Java Support
• No naming support
3/3/2009 http://ltsllc.com/slides/ipc.html 41

42. Message Queue Details
• Synchronization
– Accept, read, write
– 25 usec
• Bandwidth
– 167 MB/sec
3/3/2009 http://ltsllc.com/slides/ipc.html 42

43. Platform Differences
• Direction
– Linux is one-way
– Windows is two-way
• Naming
– Linux: any
– Windows: must be .pipename
• Misc
– Windows pipes are networkable
3/3/2009 http://ltsllc.com/slides/ipc.html 43

44. Message Queues: CLIP
• MessageQueue class
• One direction
• File naming
• JNI under the hood
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45. Message Queues vs. Shared
Memory
• Less bandwidth
– Synchronized: 250MB vs. 167MB
– Unsynchronized: 1000MB vs. 167MB
• No Java support
• Platform differences
3/3/2009 http://ltsllc.com/slides/ipc.html 45

46. Semaphores
3/3/2009 http://ltsllc.com/slides/ipc.html 46

47. Semaphores
• Synchronization only
• Any to any
• Access via increment/decrement
• No Java support
• No naming support
3/3/2009 http://ltsllc.com/slides/ipc.html 47

48. Semaphore Details
• Integer value
• Decrement reserves
– Blocks if the value is 0 or less
• Increment releases
– May wake a blocked process
• N-ary semaphores
– Values other than 0 or 1
3/3/2009 http://ltsllc.com/slides/ipc.html 48

49. Semaphore Details
• Synchronization
– 25 usec
• Platform naming differences
– Linux: /somename
– Windows: somename
– Ad hoc access control
3/3/2009 http://ltsllc.com/slides/ipc.html 49

50. Semaphores CLIP
• Semaphore class
• File system naming
• JNI under the hood
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51. Example: The Liminator
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52. The Liminator: Requirements
• Start with Google Maps
• Too many processes == poor performance
• Limit processes with a semaphore
– Initial value = max number of processes
– Reserve when trying to spawn
– Release when complete
3/3/2009 http://ltsllc.com/slides/ipc.html 52

53. Liminator: Design
Semaphore
Client Client
Client Client
Client Client
Client Client
Client Client
Client Client
Running
Waiting
3/3/2009 http://ltsllc.com/slides/ipc.html 53

54. Semaphores vs Shared Memory
• About the same speed
• No naming support
• No JRE support
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55. Summary
3/3/2009 http://ltsllc.com/slides/ipc.html 55

56. Summary
• IPC
– Multiple processes
– Naming
– Bandwidth
• CLIP
– Open source Linux & Windows
– New primitives via JNI
– Simplify others
3/3/2009 http://ltsllc.com/slides/ipc.html 56

57. Summary of IPC Types
IPC Type Sync Band Java
Support?
Semaphores 25 usec N/A No
Sockets 70 usec 15MB Yes
Message Queues 25 usec 167MB No
Shared Memory 25 usec 250MB Yes
3/3/2009 http://ltsllc.com/slides/ipc.html 57

58. Resources
Slides & code ltsllc.com/talks/ipc
Windows msdn.microsoft.com
Linux Advanced UNIX Programming
basepath.com/aup/index.htm
Java JTUX
basepath.com/aup/jtux
Sun Forums java.sun.com
Code Project codeproject.com
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59. The End
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60. Which Option is Best?
No
Shared
Sync?
Memory
Yes
Yes Yes Yes
Data? > 10MB/s? 1-to-1?
No No No
Shared Message
Semaphores Sockets
Memory* Queues
3/3/2009 http://ltsllc.com/slides/ipc.html 60