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Angel-C-Interface_en.md

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Currently, many main-stream deep-learning libraries are implemented in C/C++. In order to make Angel parameter server available for these libraries, it is necessary to provide C/C++ interfaces for these libraries to start Angel and call the corresponding interfaces from internal.

Angel is developed with Java, and currently has implemented a basic interface that can start PSAgent, send model delta and get parameters.

  • need JNI if called with C
  • support multithreading environment; The JNI JavaVM objects can be shared across threads, whereas JNIEnv can't
  • abstract out the C version of the PSAgent and MatrixClient classes or interfaces
  • PSAgent ensures that each process starts only one instance

The specific interfaces are as follows:

C/C++ Interfaces

PSAgent Initialization and Start-up

  1. Initialization

    	PSAgent psAgent = new PSAgent(conf, masterIp, masterPort, clientIndex);
	conf:Configuration //Angel system configuration
	masterIp:String //Angel app master IP address
	masterPort:int //Angel app master port
	clientIndex:int //client index (globally unique)

  2. Start-up

    psAgent.initAndStart();

Matrix Operations

  1. getMatrixClient

    	MatrixClient matrixClient = psAgent.getMatrixClient(matrixName, taskIndex);
	matrixName:String
	taskIndex:int task //index the (globally unique) task execution unit, used by sync control (BSP, SSP)

  2. Matrix Interfaces

    	//Set every element in the matrix to a random number
	public void random(int range) throws Exception;

	//Set every element in the matrix to 0
	public void zero() throws Exception;

	//Update the matrix
	public void increment(double[] delta) throws Exception;

	//Update the matrix by index
	public void increment(int[] indexes, double[] delta) throws Exception;

	//Get the matrix by index
	public double[] get(int[] indexes) throws Exception;

	//Get the matrix
	public double[] get() throws Exception;

	//Update the model delta in PSAgent's local cache to PS
	public Future<VoidResult> flush() throws Exception;

	//Update the model delta in PSAgent's local cache to PS and update the clock
	public Future<VoidResult> clock() throws Exception;

	//Aggregate UDF, for example, sum, max
	public AggrResult aggr(AggrFunc func) throws Exception;

	//UDF for matrix updating, for example, scalar, increment
	public Future<VoidResult> update(UpdaterFunc func) throws Exception;