src/main/java/org/apache/sysds/runtime/controlprogram/federated/ExecutionContextMap.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.sysds.runtime.controlprogram.federated;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.sysds.runtime.controlprogram.context.ExecutionContext;
import org.apache.sysds.runtime.controlprogram.context.ExecutionContextFactory;

public class ExecutionContextMap {
	private final ExecutionContext _main;
	private final Map<Long, ExecutionContext> _parEc;
	
	public ExecutionContextMap() {
		_main = createExecutionContext();
		_parEc = new ConcurrentHashMap<>();
	}
	
	public ExecutionContext get(long tid) {
		//return main execution context
		if( tid <= 0 )
			return _main;
		
		//atomic probe, create if necessary, and return
		return _parEc.computeIfAbsent(tid,
			k -> deriveExecutionContext(_main));
	}
	
	private static ExecutionContext createExecutionContext() {
		ExecutionContext ec = ExecutionContextFactory.createContext();
		ec.setAutoCreateVars(true); //w/o createvar inst
		return ec;
	}
	
	private static ExecutionContext deriveExecutionContext(ExecutionContext ec) {
		//derive execution context from main to make shared variables available
		//but allow normal instruction processing and removal if necessary
		ExecutionContext ec2 = ExecutionContextFactory
			.createContext(ec.getVariables(), ec.getProgram());
		ec2.setAutoCreateVars(true); //w/o createvar inst
		return ec2;
	}
}