Verify if a process is running using its PID in JAVA

Question

I'm currently building an application in JAVA where there can be only one execution. So I'm currently using a lock file in which I write the PID of the current execution.

So whenever this application will start, it will open the file (if it exists) and try to detect if the PID written in the file is actually running.

This prevent the problem where my app crash before unlocking the file.

I need this to work both on windows (XP,7 or 8) and linux (all the users are on debian based distros).

Here's some code to give you a better picture of what I want to do :

//get the PID from the file
int pidValue = new FileReader(file).read();

//get the OS type
String os = System.getProperty("os.name").toLowerCase();

//Check PID depending of OS type
if( os.contains("nux") || os.contains("nix") ){
/*
 * Check PID on Linux/Unix
*/
} else if ( os.contains("win") ) {
/*
 * Check PID on Windows
 */
}

I have tried to find documentation on the subject, but I didn't manage to find anything useful yet.

Thank you very much.

Answer 1

The following code determines if a process with the specified pid is running. It was tested on Windows 7 and Ubuntu 13. On Windows it uses apache commons-exec to run tasklist and determines if they found the specified pid based on their exit code. It overcomes the fact that tasklist always returns 0 by piping the result to findstr. On linux it uses ps to do the same thing. It also suppresses stdout logging of the child process.

public static boolean isProcessRunning(int pid, int timeout, TimeUnit timeunit) throws java.io.IOException {
    String line;
    if (OS.isFamilyWindows()) {
        //tasklist exit code is always 0. Parse output
        //findstr exit code 0 if found pid, 1 if it doesn't
        line = "cmd /c \"tasklist /FI \"PID eq " + pid + "\" | findstr " + pid + "\"";
    }
    else {
        //ps exit code 0 if process exists, 1 if it doesn't
        line = "ps -p " + pid;
            //`-p` is POSIX/BSD-compliant, `--pid` isn't<ref>https://github.com/apache/storm/pull/296#discussion_r20535744</ref>
    }
    CommandLine cmdLine = CommandLine.parse(line);
    DefaultExecutor executor = new DefaultExecutor();
    // disable logging of stdout/strderr
    executor.setStreamHandler(new PumpStreamHandler(null, null, null));
    // disable exception for valid exit values
    executor.setExitValues(new int[]{0, 1});
    // set timer for zombie process
    ExecuteWatchdog timeoutWatchdog = new ExecuteWatchdog(timeunit.toMillis(timeout));
    executor.setWatchdog(timeoutWatchdog);
    int exitValue = executor.execute(cmdLine);
    // 0 is the default exit code which means the process exists
    return exitValue == 0;
}

Answer 2

Please see below ready to copy/paste example.

Boolean method isStillAllive(...) will get as a parameter the process id number(pid). Method call is quite generic and is meant to wrap device dependent logic to solve same problem on windows/linux/unix like operating systems.

public boolean isStillAllive(String pidStr) {
    String OS = System.getProperty("os.name").toLowerCase();
    String command = null;
    if (OS.indexOf("win") >= 0) {
        log.debug("Check alive Windows mode. Pid: [{}]", pidStr);
        command = "cmd /c tasklist /FI \"PID eq " + pidStr + "\"";            
    } else if (OS.indexOf("nix") >= 0 || OS.indexOf("nux") >= 0) {
        log.debug("Check alive Linux/Unix mode. Pid: [{}]", pidStr);
        command = "ps -p " + pidStr;            
    } else {
        log.warn("Unsuported OS: Check alive for Pid: [{}] return false", pidStr);
        return false;
    }
    return isProcessIdRunning(pidStr, command); // call generic implementation
}

Actual call to system is delegated to isProcessIdRunning(). This method will invoke preformed system dependent command in generic way and result obtained from system is consumed and parsed line by line. If at least one of response lines contains pid than we interpret this as success.

private boolean isProcessIdRunning(String pid, String command) {
    log.debug("Command [{}]",command );
    try {
        Runtime rt = Runtime.getRuntime();
        Process pr = rt.exec(command);

        InputStreamReader isReader = new InputStreamReader(pr.getInputStream());
        BufferedReader bReader = new BufferedReader(isReader);
        String strLine = null;
        while ((strLine= bReader.readLine()) != null) {
            if (strLine.contains(" " + pid + " ")) {
                return true;
            }
        }

        return false;
    } catch (Exception ex) {
        log.warn("Got exception using system command [{}].", command, ex);
        return true;
    }
}