Thread Safe Interprocess Shared Memory in Java (in 7 mins)

Thread Safe Interprocess Shared Memory in Java (in 7 mins)

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  Thread Safe Interprocess SharedMemory in Java (in 7 minutes) Peter Lawrey Principal Consultant Higher Frequency Trading January 2014 Thread Safe Interprocess Shared Memory in Java 1
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  Shared Memory     Java naturallyuses memory on the heap (and stack) Java can also access memory mapped files These files can be accessed and shared by multiple processes at once They can be persisted, or stored on a tmpfs or RAM drive January 2014 Thread Safe Interprocess Shared Memory in Java 2
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  Thread Safe   Java's threadsafe constructs are all on the heap You can use Unsafe and create off heap thread safe constructs such as memory barriers, volatile access and CAS operations January 2014 Thread Safe Interprocess Shared Memory in Java 3
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  What is CAS?    CASis Compare And Swap also known as Compare And Set in some Java libraries It is a thread safe operation which only succeeds for one thread at a time and can be used to build a lock Is a single machine code instruction → fast January 2014 Thread Safe Interprocess Shared Memory in Java 4
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  Why not usethe heap?  Can support 100s of GB with no GC impact  Can share data structures between processes  Can persist data without extra overhead This allows you to implement a simple embedded database with sub micro-second read/write latency January 2014 Thread Safe Interprocess Shared Memory in Java 5
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  sun.misc.Unsafe public native compareAndSetInt( Objectobj, // can be null long offset, int expected, int value); Also compareAndSetLong Likely to go away in Java 9 January 2014 Thread Safe Interprocess Shared Memory in Java 6
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  Bytes OpenHFT/Java-Lang has awrapper  64-bit replacement for ByteBuffer  Thread safe operations  Supports binary data, text parsing and object serialization. e.g. ObjectInput/Ouput January 2014 Thread Safe Interprocess Shared Memory in Java 7
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  Demo - LockingViaMMapMain Twoprocesses toggle flags in many locked records One process flips false → true The other flips true → false Toggled 100,000,000 times with an average delay of 49 ns January 2014 Thread Safe Interprocess Shared Memory in Java 8
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  Questions? @PeterLawrey github.com/OpenHFT Thank you to SkillsMatter– the host RecWorks – the organisers LJC – London Java Community January 2014 Thread Safe Interprocess Shared Memory in Java 9
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  Questions? @PeterLawrey github.com/OpenHFT Thank you to SkillsMatter– the host RecWorks – the organisers LJC – London Java Community January 2014 Thread Safe Interprocess Shared Memory in Java 9