multithreading - How to set a time limit on a java function running a regex

Question

I am running a regex in a java function to parse a document and return true if it has found the string specified by the regex and return false if it hasn't. But the problem is that when the document doesn't contain the string specified by the regex It takes a very long time to return false and I want to terminate that function if it takes more than 6 seconds to execute.

How can I set a time limit of 6 seconds on that function so as to forcibly terminate that if it takes more than 6 seconds.

I am calling a method "method 1" of class 2 from class 1. The "method 1" calls "method 2" of the same class i.e. "class 2". Method 2 runs the regex code over a document. If it finds the string specified by the regex, then it returns the result to the method 1 which in turn return the result to the method in "class 1" which called the "method 1" of class 2. Now the problem is that the execution time of both the method1 and method2 of class 2 should be not more than 6 seconds.

So, I made a new RegexpThread class in the same file, in which my class2 was. Then I move the method2 of the class2 into class RegexpThread. Then whenever the method 1 is called, it instantiates the RegexpThread class as follows:

RegexpThread rt = new RegexpThread() {
    public void run() {
        method 2(m, urlCopy, document);
    }    
};

rt.start();

try {
    rt.join(6 * 1000);
} catch (InterruptedException e) {
    return "y";
}

if(rt.getResultXml().equals("")) {
    return "g";
}

resultXml.append(rt.getResultXml());

return resultXml.toString();

The code shown is in the method 1 of class2. The method 2 in the RegexpThread class perform some regex search over a document. There is a private field named "resultXml" in the RegexpThread class. If the method 2 has found the string specified by the regex then it assigns the result to the private field "resultXml". If not then the "resultXml" contains its default value i.e empty string.

So, in the above "if block", it is checking the "resultXml" field against empty string. If it is an empty string then that means the regex has not found its string in the document. But if it is not an empty string then that means the regex has found the string in the document and has assigned the result to the "resultXml" field.

so, look at this and tell me what to do...

Answer 1

I might be mistaken here, but I think all ways to terminate a thread have been deprecated for some time. The recommended way is to use a shared isRunning variable that your worker thread periodically checks and gracefully exits when it's been set.

This will not work in your case, but it looks to me like you're treating the symptom - not the real problem. You should post the code of your regexp function, that takes 6 seconds to execute. If it's the regexp itself, the execution time may be a case of catastrophic backtracking.