Java IPC and the CLIP library

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

Who Gives a Damn?

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

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

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

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

Java RandomAccessFile raf = new RandomAccessFile(\"/temp/smfile\", \"rw\"); 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); 3/3/2009 http://ltsllc.com/slides/ipc.html 7

CLIP SharedMemory smem = new SharedMemory(\"/temp/smfile\"); 3/3/2009 http://ltsllc.com/slides/ipc.html 8

What is IPC? Inter-Process Communication (IPC) • Multiple processes • Naming • Synchronization • Bandwidth 3/3/2009 http://ltsllc.com/slides/ipc.html 9

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

Naming How do you… • Connect processes together? • Determine who is allowed to connect? • Examples – TCP/IP? – Email? – Telephones? 3/3/2009 http://ltsllc.com/slides/ipc.html 11

File Naming Many IPC methods use the file system because • Visible to all processes • Has access control built in 3/3/2009 http://ltsllc.com/slides/ipc.html 12

File Naming Examples • Memory Mapped Files • Named Pipes/FIFOs 3/3/2009 http://ltsllc.com/slides/ipc.html 13

Synchronization • Event ordering • Mutual exclusion 3/3/2009 http://ltsllc.com/slides/ipc.html 14

Example: Online Purchase 1. Get user credit information 2. Decision purchase 3. Update credit information 3/3/2009 http://ltsllc.com/slides/ipc.html 15

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

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 3/3/2009 http://ltsllc.com/slides/ipc.html 17

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 3/3/2009 http://ltsllc.com/slides/ipc.html 18

Which Type of IPC is Appropriate? 3/3/2009 http://ltsllc.com/slides/ipc.html 19

IPC Types • Shared Memory • Semaphores • Sockets • Message Queues 3/3/2009 http://ltsllc.com/slides/ipc.html 20

Shared Memory 3/3/2009 http://ltsllc.com/slides/ipc.html 21

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

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

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 3/3/2009 http://ltsllc.com/slides/ipc.html 24

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 3/3/2009 http://ltsllc.com/slides/ipc.html 25

Example: World of Warcraft! Shared Memory! 3/3/2009 http://ltsllc.com/slides/ipc.html 26

WoW: Requirements • One client process per player • One server process for all • Server periodically reads all orders • Server issues results 3/3/2009 http://ltsllc.com/slides/ipc.html 27

WoW: Design Client Orders (EvilOne) Player Order EvilOne kill Client Lancelot kill (Lancelot) Client Martha Stewart kill (Conan) Conan make cookies … Client (Martha) 3/3/2009 http://ltsllc.com/slides/ipc.html 28

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

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

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

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

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

Sockets: CLIP • Some utility classes – ThreadedSocketServer • JRE already has excellent support 3/3/2009 http://ltsllc.com/slides/ipc.html 34

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

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

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

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

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

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

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

Message Queues: CLIP • MessageQueue class • One direction • File naming • JNI under the hood 3/3/2009 http://ltsllc.com/slides/ipc.html 44

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

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

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

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

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

Semaphores CLIP • Semaphore class • File system naming • JNI under the hood 3/3/2009 http://ltsllc.com/slides/ipc.html 50

Example: The Liminator 3/3/2009 http://ltsllc.com/slides/ipc.html 51

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

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

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

Summary 3/3/2009 http://ltsllc.com/slides/ipc.html 55

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

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

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 3/3/2009 http://ltsllc.com/slides/ipc.html 58

The End 3/3/2009 http://ltsllc.com/slides/ipc.html 59

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

Java IPC and the CLIP library

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