[MINOR] Only Warn Once On Inefficient ThreadPool Use

This commit change the warning to only occur once when
allocating a threadpool on a non main thread.

Closes #2160

Signed-off-by: Sebastian Baunsgaard <[email protected]>

Author: Baunsgaard

src/main/java/org/apache/sysds/runtime/util/CommonThreadPool.java

@@ -70,6 +70,9 @@ public class CommonThreadPool implements ExecutorService {
 	/** This common thread pool */
 	private final ExecutorService _pool;
 
+	/** Local variable indicating if there was a thread that was not main, and requested a thread pool */
+	private static boolean incorrectPoolUse = false; 
+
 	/**
 	 * Constructor of the threadPool. This is intended not to be used except for tests. Please use the static
 	 * constructors.
@@ -122,7 +125,10 @@ else if(mainThread || threadName.contains("PARFOR")) {
 		}
 		else {
 			// If we are neither a main thread or parfor thread, allocate a new thread pool
-			LOG.warn("An instruction allocated it's own thread pool indicating that some task is not properly reusing the threads.");
+			if(!incorrectPoolUse){
+				LOG.warn("An instruction allocated it's own thread pool indicating that some task is not properly reusing the threads.");
+				incorrectPoolUse = true;
+			}
 			return Executors.newFixedThreadPool(k);
 		}