How to timeout a thread in Java / Limiting a threads execution time

For some code you may want to limit its execution time, to prevent infinite loops that can’t be detected within the code. I ran in to this issue with HTMLCleaner on certain HTML, which due to the architecture could not keep track of possible loops with a counter.

The code will need to handle thread interrupts internally by checking Thread.interrupted(), so it won’t always work on arbitrary code.

import java.util.concurrent.*;

class HTMLParseTask implements Callable<Document> {
    String html

    HTMLParseTask(String html) {
        this.html = html;
    }

    @Override
    Document call() throws Exception {
        TagNode tagNode = cleaner.clean(html);
        return domSerializer.createDOM(tagNode);
    }
}

public Document clean(String html) {
    if(html == null) return null;
    // limit the html cleaning to 5s, to avoid any bad html causing infinite loops
    ExecutorService executor = Executors.newSingleThreadExecutor();
    Future<String> future = executor.submit(new HTMLParseTask(html));
    Document result = null;
    try {
        result = future.get(5, TimeUnit.SECONDS);
    } catch(TimeoutException ex) {
        future.cancel(true); // cancel and send a thread interrupt
        log.error("Error parsing HTML. Timed out");
    } finally {
        executor.shutdownNow();
    }
    return result;
}