Java-Affinity ============= Lets you bind a thread to a given core, this can improve performance ( this libary works best on linux ) OpenHFT Java Thread Affinity library See the affinity/src/test/java for working examples of how to use this library. ## Versions V2.2 - Latest build. V2.0.1 - Added getThreadId for the process if of the thread. ### Installing JNA on Ubuntu ---- sudo apt-get install libjna-java ---- ### Installing JAN on Centos ---- sudo yum install jna ---- ## How does allocation work? The library will read your /proc/cpuinfo if you have one or provide one and it will determine your CPU layout. If you don't have one it will assume every CPU is on one Socket. The library looks for isolated CPUs determined by looking at the CPUs you are not running on by default. i.e. if you have 16 CPUs but 8 of them are not available for general use (as determined by the affinity of the process on startup) it will start assigning to those CPUs. Note: if you have more than one process using this library you need to specify which CPUs the process can use otherwise it will assign the same CPUs to both processes. To control which CPUs a process can use, add -Daffinity.reserved={cpu-mark-in-hex} to the command line of the process Note: the CPU 0 is reserved for the Operating System, it has to run somewhere. ## Acquiring a CPU lock for a thread You can acquire a lock for a CPU in the following matter In Java 6 AffinityLock al = AffinityLock.acquireLock(); try { // do some work locked to a CPU. } finally { al.release(); } In Java 7 or 8 try (AffinityLock al = AffinityLock.acquireLock()) { // do some work while locked to a CPU. } You have further options such as ## Acquiring a CORE lock for a thread You can reserve a whole core. If you have hyper-threading enabled, this will use one CPU and leave it's twin CPU unused. try (AffinityLock al = AffinityLock.acquireCore()) { // do some work while locked to a CPU. } ## Controlling layout You can chose a layout relative to an existing lock. try (final AffinityLock al = AffinityLock.acquireLock()) { System.out.println("Main locked"); Thread t = new Thread(new Runnable() { @Override public void run() { try (AffinityLock al2 = al.acquireLock(AffinityStrategies.SAME_SOCKET, AffinityStrategies.ANY)) { System.out.println("Thread-0 locked"); } } }); t.start(); } In this example, the library will prefer a free CPU on the same Socket as the first thread, otherwise it will pick any free CPU. ## Getting the thread id. You can get the current thread id using int threadId = AffinitySupport.getThreadId(); ## determining which CPU you are running on. You can get the current CPU being used by int cpuId = AffinitySupport.getCpu(); ## Controlling the affinity more directly. The affinity of the process on start up is long baseAffinity = AffinityLock.BASE_AFFINITY; The available CPU for reservation is long reservedAffinity = AffinityLock.RESERVED_AFFINITY; If you want to get/set the affinity directly you can do long currentAffinity = AffinitySupport.getAffinity(); AffinitySupport.setAffinity(1L << 5); // lock to CPU 5. # Support Material [Java Thread Affinity support group](https://groups.google.com/forum/?hl=en-GB#!forum/java-thread-affinity) For an article on how much difference affinity can make and how to use it http://vanillajava.blogspot.com/2013/07/micro-jitter-busy-waiting-and-binding.html # Questions and Answers ## Question I am currently working on a project related to deadlock detection in multithreaded programs in java. We are trying to run threads on different processors and thus came across your github posts regarding the same. https://github.com/peter-lawrey/Java-Thread-Affinity/wiki/Getting-started Being a beginner, I have little knowledge and thus need your assistance. We need to know how to run threads on specified cpu number and then switch threads when one is waiting. ## Answer Use : ``` java AffinityLock.setAffinity (1L << n); ``` where n is the cpu you want to run the thread on.